Phylogeography and reproductive isolation of the brown mussel, Perna perna, on the South African coastline
- Authors: Barker, Cassandra
- Date: 2021-10
- Subjects: Mexilhao mussel South Africa , Phylogeography South Africa , Mexilhao mussel Reproduction , Mexilhao mussel Genetics , Intertidal organisms South Africa , Mexilhao mussel Climatic factors South Africa , Cytochrome oxidase , Mitochondrial DNA , Haplotype network
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/190041 , vital:44958
- Description: Maintenance of a species’ abundance and adaptive potential is partially dependent on its genetic diversity. Distinct genetic lineages within a species can differ significantly in their resistance and resilience to environmental pressure. An assessment of such differences is key to grasp the adaptive potential of a species. Physical environmental conditions are significant determinants of the distribution of species and their genetic lineages. Under climate change scenarios, the assessment of the temporal stability of the spatial distribution of genetic structure has important consequences for conservation as it offers key insights into the adaptive potential and evolutionary capacity of a species. This thesis investigated the phylogeography and reproductive isolation of Perna perna, the brown mussel. This species is an ecologically and economically important intertidal mussel on South Africa’s coastline. It was determined in 2007 that there were two distinct genetic lineages of P. perna present on South Africa’s coastline, the Eastern and Western lineage. This thesis compared mitochondrial DNA between samples collected in 2007 and samples collected in 2019 to determine differences in genetic structure of P. perna over time. This thesis further investigated the reproductive timing of the two lineages to determine if this contributes to the maintenance of the genetic structure of this species. The results show that there is a shift in the distribution of the Eastern lineage since 2007, an increase in the range of the overlap region, and there was a change in genetic diversity in the form of private haplotypes between 2007 and 2019. The lineages have unsynchronised spawning and reproductive patterns are more closely linked to changes in temperature. While the lineages have shown slight distributional changes over time, the influence of environmental conditions and the predicted changes in sea surface temperatures could see a change in future populations’ fitness and dispersal. Thus, changes in sea surface temperature could affect reproductive timing and the future genetic stability of the species. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2021
- Full Text:
- Date Issued: 2021-10
- Authors: Barker, Cassandra
- Date: 2021-10
- Subjects: Mexilhao mussel South Africa , Phylogeography South Africa , Mexilhao mussel Reproduction , Mexilhao mussel Genetics , Intertidal organisms South Africa , Mexilhao mussel Climatic factors South Africa , Cytochrome oxidase , Mitochondrial DNA , Haplotype network
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/190041 , vital:44958
- Description: Maintenance of a species’ abundance and adaptive potential is partially dependent on its genetic diversity. Distinct genetic lineages within a species can differ significantly in their resistance and resilience to environmental pressure. An assessment of such differences is key to grasp the adaptive potential of a species. Physical environmental conditions are significant determinants of the distribution of species and their genetic lineages. Under climate change scenarios, the assessment of the temporal stability of the spatial distribution of genetic structure has important consequences for conservation as it offers key insights into the adaptive potential and evolutionary capacity of a species. This thesis investigated the phylogeography and reproductive isolation of Perna perna, the brown mussel. This species is an ecologically and economically important intertidal mussel on South Africa’s coastline. It was determined in 2007 that there were two distinct genetic lineages of P. perna present on South Africa’s coastline, the Eastern and Western lineage. This thesis compared mitochondrial DNA between samples collected in 2007 and samples collected in 2019 to determine differences in genetic structure of P. perna over time. This thesis further investigated the reproductive timing of the two lineages to determine if this contributes to the maintenance of the genetic structure of this species. The results show that there is a shift in the distribution of the Eastern lineage since 2007, an increase in the range of the overlap region, and there was a change in genetic diversity in the form of private haplotypes between 2007 and 2019. The lineages have unsynchronised spawning and reproductive patterns are more closely linked to changes in temperature. While the lineages have shown slight distributional changes over time, the influence of environmental conditions and the predicted changes in sea surface temperatures could see a change in future populations’ fitness and dispersal. Thus, changes in sea surface temperature could affect reproductive timing and the future genetic stability of the species. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2021
- Full Text:
- Date Issued: 2021-10
Potential Synergism between Entomopathogenic Fungi and Entomopathogenic Nematodes for the control of false codling moth (Thaumatotibia leucotreta)
- Authors: Prinsloo, Samantha Lee
- Date: 2021-10
- Subjects: Cryptophlebia leucotreta , Entomopathogenic fungi , Insect nematodes , Citrus Diseases and pests , Cryptophlebia leucotreta Biological control , Pests Integrated control , Biological pest control agents
- Language: English
- Type: Masters theses , text
- Identifier: http://hdl.handle.net/10962/188832 , vital:44790
- Description: False codling moth, Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) (FCM), is a major phytosanitary pest of citrus in South Africa. Sufficient control measures for the soil-dwelling life stages of FCM have yet to be identified and owing to restrictions on the use of insecticides, non-chemical control options have been investigated including the use of entomopathogenic fungi (EPF) and entomopathogenic nematodes (EPN). Laboratory and field trials on an indigenous EPF, Metarhizium anisopliae FCM Ar 23 B3, have shown that this isolate is capable of inducing mortality in FCM soil-dwelling life stages. Other agents that have been highlighted as potential controls for soil-dwelling FCM life stages are the EPN species Steinernema yirgalemense 157-C, S. jeffreyense J194 and H. noenieputensis 158-C. This study conducted laboratory bioassays to assess the virulence of these four control agents on fifth instar FCM, in 24-well plates. These results reaffirmed the virulence of the four microbial control agents at their recommended doses of 50 IJs (EPN) and 1×107 conidia/ml (EPF) against fifth instar FCM with 80 to 96% larval mortality recorded. The EPF isolate exhibited the lowest mortality whilst S. yirgalemense induced the greatest mortality. In addition, the lethal concentration (LC) values for each isolate were determined using dose response bioassays. These values were previously unknown for all EPN species and for the EPF isolate based on the methodology used in this study. The LC50 results in order from lowest to highest EPN IJ concentration requirements were 4.38 IJs (S. yirgalemense), 4.47 IJs (S. jeffreyense) and 7.11 IJs (H. noenieputensis). The EPF isolate exhibited an LC50 of 3.42×105 conidia/ml. Lastly, research has shown that the combination of two control agents may increase control of late instar lepidopteran and coleopteran larvae, through synergistic interactions. Thus, the interactions that occurred between the combination of these EPN species with the EPF isolate were determined. This study found that when all three EPN species were combined simultaneously and sequentially with the EPF isolate M. anisopliae FCM AR 23 B3, additive interactions took place with exception of the simultaneous application of S. yirgalemense and H. noenieputensis, with the EPF and S. jeffreyense applied 24 h post EPF application. For the former, a synergistic interaction was found, whilst for the latter two, an antagonistic interaction. Although no strongly synergistic interactions were observed, additive interactions have been shown to reach a synergistic level when certain parameters are changed. Moving forward, a uniform methodology for conducting EPF/EPN interaction experiments has been suggested. It has also been recommended that due to the additive interactions observed in this study, laboratory soil-bioassays and field trials should be carried out for all three EPN species in combination with the EPF isolate. This research will inevitably facilitate the constant knowledge into management strategies for the phytosanitary pest, FCM in South African citrus. , Thesis (MSc) -- Science, Zoology and Entomology, 2021
- Full Text:
- Date Issued: 2021-10
- Authors: Prinsloo, Samantha Lee
- Date: 2021-10
- Subjects: Cryptophlebia leucotreta , Entomopathogenic fungi , Insect nematodes , Citrus Diseases and pests , Cryptophlebia leucotreta Biological control , Pests Integrated control , Biological pest control agents
- Language: English
- Type: Masters theses , text
- Identifier: http://hdl.handle.net/10962/188832 , vital:44790
- Description: False codling moth, Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) (FCM), is a major phytosanitary pest of citrus in South Africa. Sufficient control measures for the soil-dwelling life stages of FCM have yet to be identified and owing to restrictions on the use of insecticides, non-chemical control options have been investigated including the use of entomopathogenic fungi (EPF) and entomopathogenic nematodes (EPN). Laboratory and field trials on an indigenous EPF, Metarhizium anisopliae FCM Ar 23 B3, have shown that this isolate is capable of inducing mortality in FCM soil-dwelling life stages. Other agents that have been highlighted as potential controls for soil-dwelling FCM life stages are the EPN species Steinernema yirgalemense 157-C, S. jeffreyense J194 and H. noenieputensis 158-C. This study conducted laboratory bioassays to assess the virulence of these four control agents on fifth instar FCM, in 24-well plates. These results reaffirmed the virulence of the four microbial control agents at their recommended doses of 50 IJs (EPN) and 1×107 conidia/ml (EPF) against fifth instar FCM with 80 to 96% larval mortality recorded. The EPF isolate exhibited the lowest mortality whilst S. yirgalemense induced the greatest mortality. In addition, the lethal concentration (LC) values for each isolate were determined using dose response bioassays. These values were previously unknown for all EPN species and for the EPF isolate based on the methodology used in this study. The LC50 results in order from lowest to highest EPN IJ concentration requirements were 4.38 IJs (S. yirgalemense), 4.47 IJs (S. jeffreyense) and 7.11 IJs (H. noenieputensis). The EPF isolate exhibited an LC50 of 3.42×105 conidia/ml. Lastly, research has shown that the combination of two control agents may increase control of late instar lepidopteran and coleopteran larvae, through synergistic interactions. Thus, the interactions that occurred between the combination of these EPN species with the EPF isolate were determined. This study found that when all three EPN species were combined simultaneously and sequentially with the EPF isolate M. anisopliae FCM AR 23 B3, additive interactions took place with exception of the simultaneous application of S. yirgalemense and H. noenieputensis, with the EPF and S. jeffreyense applied 24 h post EPF application. For the former, a synergistic interaction was found, whilst for the latter two, an antagonistic interaction. Although no strongly synergistic interactions were observed, additive interactions have been shown to reach a synergistic level when certain parameters are changed. Moving forward, a uniform methodology for conducting EPF/EPN interaction experiments has been suggested. It has also been recommended that due to the additive interactions observed in this study, laboratory soil-bioassays and field trials should be carried out for all three EPN species in combination with the EPF isolate. This research will inevitably facilitate the constant knowledge into management strategies for the phytosanitary pest, FCM in South African citrus. , Thesis (MSc) -- Science, Zoology and Entomology, 2021
- Full Text:
- Date Issued: 2021-10
The tuber-feeding weevil Listronotus frontalis as a candidate biological control agent for the invasive semi-aquatic plant Sagittaria platyphylla within South Africa
- Authors: Rogers, Daniel James
- Date: 2021-10
- Subjects: Listronotus South Africa , Arrowhead (Plants) South Africa , Arrowhead (Plants) Biological control South Africa , Invasive plants Biological control South Africa , Insects as biological pest control agents South Africa , Plant populations South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/190731 , vital:45023
- Description: Sagittaria platyphylla (Engelm.) J.G.Sm. (Alismataceae) is an invasive, aquatic macrophyte originating in the southern United States of America. In South Africa, the plant was first detected in Krantzkloof Nature Reserve, KwaZulu-Natal Province in 2008, and due to its known impact in other countries, it was listed as a Category 1a invader species under the National Environmental Management: Biodiversity Act 2004 (NEM:BA). This invasive plant has proved difficult to manage due to its varied growth forms and reproductive strategies, such as prolific seed and below ground tuber production. Due to the limitations of conventional control mechanisms, biological control is currently being considered as a potential control option. The tuber feeding weevil Listronotus frontalis LeConte (Coleoptera: Curculionidae) has been identified as a candidate biological control agent for this invasive species. The aims of this study were twofold; to firstly determine the importance of tubers to S. platyphylla populations growing in South Africa; and secondly, to determine the biology and suitability of L. frontalis, a tuber feeder, as a candidate biological control agent. Surveys of S. platyphylla populations in South Africa showed that tubers were found in all sampled sites, except for Krantzkloof Nature reserve in KwaZulu-Natal Province. The highest number of tubers was 97.75 ± 10.62 (SE) m-2 recorded at Jonkershoek in the Western Cape Province. Monthly sampling from two sites in the Eastern Cape Province, the Makana Botanical Gardens and Maden Dam showed that neither season nor water depth affected tuber production. However, the mean number of tubers as well as mass of tubers sampled, were consistently higher (F(1,179) = 20.9542, P < 0.0001) and heavier (F(1, 857) = 585.7293, P < 0.0001) at the Botanical Gardens than at Maden Dam, respectively. The study showed that tubers are an important life stage of S. platyphylla populations and may vary in size and abundance between and within sites. The tuber feeding weevil was shown to develop from egg to ovipositing adult within just over 40 days. Females were recorded to lay up to 48 eggs within a period of one week. Impact studies showed that adult feeding led to a reduction in all but one of the 11 measured plant growth and developmental measurements, including a reduction in the mean mass of the above-ground plant material (F(2,2743) = 12.05, P = 0.002) as well as a reduction in size and abundance of tubers (F(2,58.47) = 9.756, P = 0.0006) and stolons(F(14.943) = 8.7577, P = 0.003). These results are encouraging and suggest that if the insect is released in South Africa, it may prove to be a valuable biocontrol agent. It is concluded that, until suitable biological control options become available in South Africa, the chemical and mechanical control measures currently implemented should continue, however, controlling tubers should be considered during the planning and implementation of these strategies. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2021
- Full Text:
- Date Issued: 2021-10
- Authors: Rogers, Daniel James
- Date: 2021-10
- Subjects: Listronotus South Africa , Arrowhead (Plants) South Africa , Arrowhead (Plants) Biological control South Africa , Invasive plants Biological control South Africa , Insects as biological pest control agents South Africa , Plant populations South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/190731 , vital:45023
- Description: Sagittaria platyphylla (Engelm.) J.G.Sm. (Alismataceae) is an invasive, aquatic macrophyte originating in the southern United States of America. In South Africa, the plant was first detected in Krantzkloof Nature Reserve, KwaZulu-Natal Province in 2008, and due to its known impact in other countries, it was listed as a Category 1a invader species under the National Environmental Management: Biodiversity Act 2004 (NEM:BA). This invasive plant has proved difficult to manage due to its varied growth forms and reproductive strategies, such as prolific seed and below ground tuber production. Due to the limitations of conventional control mechanisms, biological control is currently being considered as a potential control option. The tuber feeding weevil Listronotus frontalis LeConte (Coleoptera: Curculionidae) has been identified as a candidate biological control agent for this invasive species. The aims of this study were twofold; to firstly determine the importance of tubers to S. platyphylla populations growing in South Africa; and secondly, to determine the biology and suitability of L. frontalis, a tuber feeder, as a candidate biological control agent. Surveys of S. platyphylla populations in South Africa showed that tubers were found in all sampled sites, except for Krantzkloof Nature reserve in KwaZulu-Natal Province. The highest number of tubers was 97.75 ± 10.62 (SE) m-2 recorded at Jonkershoek in the Western Cape Province. Monthly sampling from two sites in the Eastern Cape Province, the Makana Botanical Gardens and Maden Dam showed that neither season nor water depth affected tuber production. However, the mean number of tubers as well as mass of tubers sampled, were consistently higher (F(1,179) = 20.9542, P < 0.0001) and heavier (F(1, 857) = 585.7293, P < 0.0001) at the Botanical Gardens than at Maden Dam, respectively. The study showed that tubers are an important life stage of S. platyphylla populations and may vary in size and abundance between and within sites. The tuber feeding weevil was shown to develop from egg to ovipositing adult within just over 40 days. Females were recorded to lay up to 48 eggs within a period of one week. Impact studies showed that adult feeding led to a reduction in all but one of the 11 measured plant growth and developmental measurements, including a reduction in the mean mass of the above-ground plant material (F(2,2743) = 12.05, P = 0.002) as well as a reduction in size and abundance of tubers (F(2,58.47) = 9.756, P = 0.0006) and stolons(F(14.943) = 8.7577, P = 0.003). These results are encouraging and suggest that if the insect is released in South Africa, it may prove to be a valuable biocontrol agent. It is concluded that, until suitable biological control options become available in South Africa, the chemical and mechanical control measures currently implemented should continue, however, controlling tubers should be considered during the planning and implementation of these strategies. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2021
- Full Text:
- Date Issued: 2021-10
The reproductive performance, demography and spatial ecology of an extralimital white rhinoceros population
- Authors: Truter, Anja
- Date: 2021-04
- Subjects: White rhinoceros -- South Africa -- Eastern Cape , White rhinoceros -- Effect of poaching on -- South Africa -- Eastern Cape , White rhinoceros -- South Africa -- Eastern Cape -- Reproduction , White rhinoceros -- Dispersal -- South Africa -- Eastern Cape , White rhinoceros -- Food -- South Africa -- Eastern Cape , White rhinoceros -- Behavior -- South Africa -- Eastern Cape , Spatial ecology -- South Africa -- Eastern Cape , Animal populations -- South Africa -- Eastern Cape , Endangered species -- South Africa -- Eastern Cape , Spatial behavior in animals -- South Africa -- Eastern Cape , Shamwari Game Reserve (South Africa)
- Language: English
- Type: thesis , text , Master , MSc
- Identifier: http://hdl.handle.net/10962/177975 , vital:42895
- Description: The white rhinoceros (Ceratotherium simum) (hereafter rhino) is under threat of becoming extinct due to continued poaching for its horns. In South Africa and elsewhere in Africa private landowners have, over the last few decades, contributed to the conservation of various species, including rhinos, even in areas where they have not occurred historically (i.e., where they are extralimital). Unfortunately, very few studies have investigated the conservation contribution of extralimital white rhinos on private reserves to the overall meta-population and/or their reproductive performance. The first aim of my study was therefore to determine whether or not the white rhinos introduced to a private game reserve in the Eastern Cape Province in 1992 have been successful from a reproductive perspective. I calculated inter-calving intervals, age at first calving, conception period, sex ratio, fecundity and fertility rates for white rhinos over this 28-year period. The average annual population growth rate for the rhinos was 10%, which is higher than the recommended 5% by the Rhino Management Group. Trends in density-dependent parameters such as age at first calving and inter-calving intervals also indicated that my study population is still well below carrying capacity for white rhinos and is contributing positively to white rhino conservation in South Africa. The second aim of my study was to investigate home range size and vegetation preferences of white rhinos. Home ranges were mostly larger for all age groups compared to rhinos in their native range. Previously cultivated lands (dominated by several grass species) were preferred by all rhino age groups. The rehabilitation of these previous agricultural-based pastures has likely contributed to the successful introduction of the white rhino as an extralimital megaherbivore in the Eastern Cape. I conclude that although extralimital white rhino populations in the Eastern Cape can be successful from a reproductive perspective, their potential impact on the indigenous biodiversity of the region should be a key future research priority. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2021
- Full Text:
- Date Issued: 2021-04
- Authors: Truter, Anja
- Date: 2021-04
- Subjects: White rhinoceros -- South Africa -- Eastern Cape , White rhinoceros -- Effect of poaching on -- South Africa -- Eastern Cape , White rhinoceros -- South Africa -- Eastern Cape -- Reproduction , White rhinoceros -- Dispersal -- South Africa -- Eastern Cape , White rhinoceros -- Food -- South Africa -- Eastern Cape , White rhinoceros -- Behavior -- South Africa -- Eastern Cape , Spatial ecology -- South Africa -- Eastern Cape , Animal populations -- South Africa -- Eastern Cape , Endangered species -- South Africa -- Eastern Cape , Spatial behavior in animals -- South Africa -- Eastern Cape , Shamwari Game Reserve (South Africa)
- Language: English
- Type: thesis , text , Master , MSc
- Identifier: http://hdl.handle.net/10962/177975 , vital:42895
- Description: The white rhinoceros (Ceratotherium simum) (hereafter rhino) is under threat of becoming extinct due to continued poaching for its horns. In South Africa and elsewhere in Africa private landowners have, over the last few decades, contributed to the conservation of various species, including rhinos, even in areas where they have not occurred historically (i.e., where they are extralimital). Unfortunately, very few studies have investigated the conservation contribution of extralimital white rhinos on private reserves to the overall meta-population and/or their reproductive performance. The first aim of my study was therefore to determine whether or not the white rhinos introduced to a private game reserve in the Eastern Cape Province in 1992 have been successful from a reproductive perspective. I calculated inter-calving intervals, age at first calving, conception period, sex ratio, fecundity and fertility rates for white rhinos over this 28-year period. The average annual population growth rate for the rhinos was 10%, which is higher than the recommended 5% by the Rhino Management Group. Trends in density-dependent parameters such as age at first calving and inter-calving intervals also indicated that my study population is still well below carrying capacity for white rhinos and is contributing positively to white rhino conservation in South Africa. The second aim of my study was to investigate home range size and vegetation preferences of white rhinos. Home ranges were mostly larger for all age groups compared to rhinos in their native range. Previously cultivated lands (dominated by several grass species) were preferred by all rhino age groups. The rehabilitation of these previous agricultural-based pastures has likely contributed to the successful introduction of the white rhino as an extralimital megaherbivore in the Eastern Cape. I conclude that although extralimital white rhino populations in the Eastern Cape can be successful from a reproductive perspective, their potential impact on the indigenous biodiversity of the region should be a key future research priority. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2021
- Full Text:
- Date Issued: 2021-04
Elucidating Tuta absoluta (Meyrick) invasion and enhancing its management in Eastern Africa : spread, socio-ecological impacts, and potential of a newly imported larval parasitoid for classical biological control Eastern in Africa
- Aigbedion-Atalor, Pascal Osabhahiemen
- Authors: Aigbedion-Atalor, Pascal Osabhahiemen
- Date: 2021
- Subjects: Tuta absoluta -- Biological control , Tomatoes -- Diseases and pests -- Africa, East , Braconidae , Gelechiidae -- Biological control -- Africa, East , Insects as biological pest control agents -- Africa, East
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/170421 , vital:41920 , 10.21504/10962/170421
- Description: Agriculture is a fundamental source of sustainable livelihoods in sub-Saharan Africa and millions of people in the region rely solely on small-scale farming for their food security. However, the impacts of invasive alien species (IAS) on crop production are serious, and there is no sign of this abating. Among the recent IAS that have invaded Africa in the last decade, the South American tomato pinworm Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) has been one of the most damaging. Following its first record in the Maghreb region of Africa in 2008, T. absoluta rapidly spread throughout Africa with substantial impacts on tomato production, often causing 100% yield loss. Management options adopted against T. absoluta by tomato growers in Africa have been based on the use of synthetic insecticides. While chemical insecticide applications are an important component of an integrated pest management programme, misuse and over-reliance often exacerbates the impacts of T. absolutadue to the development of resistance to commonly used active substances, increasing the fitness of the pest. This thesis sought to understand the socio-economic impacts of the spread of T. absoluta in Eastern Africa and provide effective sustainable pest management strategies to reduce its impacts below economic thresholds. Mapping surveys of Tabsoluta were conducted in 226 tomato agro-ecosystems across four eastern countries (Kenya, Sudan, Tanzania, and Uganda) Eastern Africa from 2016 to 2018 to determine the spatiotemporal distribution of the pest. The impacts of T. absoluta on the livelihoods of tomato growers were also assessed. Here, 200 tomato growers in Kenya were interviewed using a semi-structured questionnaire. Although T. absoluta, a recent invader, was distributed at high infestation levels throughout the subregion (all four countries) and was considered as the most damaging invasive alien species of agriculturally sustainable livelihoods. The arrival of T. absoluta in the subregion has resulted in livelihood losses and increased the cost of tomato production and price of the fruit, and the frequency of pesticide applications. The impact of this pest and the and the absence of effective indigenous natural enemies of the pest in Eastern Africa, was the rationale for the importation of a larval parasitoid, Dolichogenidea gelechiidivoris Marsh Syn.: Apanteles gelechiidivoris Marsh) (Hymenoptera: Braconidae), of T. absoluta from Peru into the quarantine facility of the International Centre of Insect Physiology and ecologyz(icipe), in Kenya. Pre-release assessments on the parasitzation potential of D. gelechiidivoris, encompassing host larval preference and the host suitability, and its reproductive strategy, for classical biological control of T. absoluta in Africa were conducted. Dolichogenidea gelechiidivoris females preferentially oviposited in early (1st and 2nd) larval instars of T. absoluta but parasitized and completed development in all four instars of the host. Host instar did not affect D. gelechiidivoris sex-ratio but females reared on the first instar had significantly fewer eggs than when reared in late larval instars (3rd and 4th). Females of the parasitoid emerged with a high mature egg load which peaked 2 d post-eclosion. The females of D. gelechiidivoris survived 8.51±0.65 d and produced 103±8 offspring per female at 26±4°C (range: 24 to 29°C) and 50–70% relative humidity (RH) in the presence of males and fed honey-water (80% honey). Increasing maternal age decreased the proportion of female offspring. Under the aforementioned laboratory conditions, the Gross and Net reproductive rates were 72 and 39.5 respectively, while the mean generation time was 20 d. The estimated intrinsic rate of natural increase was 0.18. These findings indicate that D. gelechiidivorisis a potential biological control agent of T. absoluta and should be considered for augmentative/inundative release in Kenya and across Africa following host specificity testing and risk assessments. The nature of the interaction between D. gelechidivoris and the predatory mirid bug Nesidiocoris tenuis(Reuter) (Hemiptera: Miridae), an important and widespread natural enemy of T. absoluta in Africa was evaluated because N. tenuis, although being a voracious predator of T. absoluta eggs, it can also prey on the early host larval instars (1st and 2nd) which are the preferred oviposition host stages of D. gelechiidivoris. Here, the impact of N. tenuis feeding on T. absoluta and the effects on D. gelechiidivoris performance was tested. Regardless of the order of introductions (i.e. the sequence of combination with D. gelechiidivoris) and densities (i.e. number of N. tenuis combined with D. gelechiidivoris), there was no intraguild predation by N. tenuis on D. gelechiidivorisas there was little host larval feeding behaviour. Also, the presence of N. tenuis did not affect the oviposition performance of D. gelechiidivoris. Further investigations revealed that the combined efficacy of N. tenuis and D. gelechiidivorison T. absoluta population was significantly higher than either natural enemy alone, thus contributes to the data supporting the release of D. gelechiidivoris in Africa. In concluding, integrating D. gelechiidivoris and N. tenuis in the management of T. absolut could potentially reduce yield losses in tomato in Eastern Africa where the socio-economic impacts of the pest are very serious.
- Full Text:
- Date Issued: 2021
- Authors: Aigbedion-Atalor, Pascal Osabhahiemen
- Date: 2021
- Subjects: Tuta absoluta -- Biological control , Tomatoes -- Diseases and pests -- Africa, East , Braconidae , Gelechiidae -- Biological control -- Africa, East , Insects as biological pest control agents -- Africa, East
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/170421 , vital:41920 , 10.21504/10962/170421
- Description: Agriculture is a fundamental source of sustainable livelihoods in sub-Saharan Africa and millions of people in the region rely solely on small-scale farming for their food security. However, the impacts of invasive alien species (IAS) on crop production are serious, and there is no sign of this abating. Among the recent IAS that have invaded Africa in the last decade, the South American tomato pinworm Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) has been one of the most damaging. Following its first record in the Maghreb region of Africa in 2008, T. absoluta rapidly spread throughout Africa with substantial impacts on tomato production, often causing 100% yield loss. Management options adopted against T. absoluta by tomato growers in Africa have been based on the use of synthetic insecticides. While chemical insecticide applications are an important component of an integrated pest management programme, misuse and over-reliance often exacerbates the impacts of T. absolutadue to the development of resistance to commonly used active substances, increasing the fitness of the pest. This thesis sought to understand the socio-economic impacts of the spread of T. absoluta in Eastern Africa and provide effective sustainable pest management strategies to reduce its impacts below economic thresholds. Mapping surveys of Tabsoluta were conducted in 226 tomato agro-ecosystems across four eastern countries (Kenya, Sudan, Tanzania, and Uganda) Eastern Africa from 2016 to 2018 to determine the spatiotemporal distribution of the pest. The impacts of T. absoluta on the livelihoods of tomato growers were also assessed. Here, 200 tomato growers in Kenya were interviewed using a semi-structured questionnaire. Although T. absoluta, a recent invader, was distributed at high infestation levels throughout the subregion (all four countries) and was considered as the most damaging invasive alien species of agriculturally sustainable livelihoods. The arrival of T. absoluta in the subregion has resulted in livelihood losses and increased the cost of tomato production and price of the fruit, and the frequency of pesticide applications. The impact of this pest and the and the absence of effective indigenous natural enemies of the pest in Eastern Africa, was the rationale for the importation of a larval parasitoid, Dolichogenidea gelechiidivoris Marsh Syn.: Apanteles gelechiidivoris Marsh) (Hymenoptera: Braconidae), of T. absoluta from Peru into the quarantine facility of the International Centre of Insect Physiology and ecologyz(icipe), in Kenya. Pre-release assessments on the parasitzation potential of D. gelechiidivoris, encompassing host larval preference and the host suitability, and its reproductive strategy, for classical biological control of T. absoluta in Africa were conducted. Dolichogenidea gelechiidivoris females preferentially oviposited in early (1st and 2nd) larval instars of T. absoluta but parasitized and completed development in all four instars of the host. Host instar did not affect D. gelechiidivoris sex-ratio but females reared on the first instar had significantly fewer eggs than when reared in late larval instars (3rd and 4th). Females of the parasitoid emerged with a high mature egg load which peaked 2 d post-eclosion. The females of D. gelechiidivoris survived 8.51±0.65 d and produced 103±8 offspring per female at 26±4°C (range: 24 to 29°C) and 50–70% relative humidity (RH) in the presence of males and fed honey-water (80% honey). Increasing maternal age decreased the proportion of female offspring. Under the aforementioned laboratory conditions, the Gross and Net reproductive rates were 72 and 39.5 respectively, while the mean generation time was 20 d. The estimated intrinsic rate of natural increase was 0.18. These findings indicate that D. gelechiidivorisis a potential biological control agent of T. absoluta and should be considered for augmentative/inundative release in Kenya and across Africa following host specificity testing and risk assessments. The nature of the interaction between D. gelechidivoris and the predatory mirid bug Nesidiocoris tenuis(Reuter) (Hemiptera: Miridae), an important and widespread natural enemy of T. absoluta in Africa was evaluated because N. tenuis, although being a voracious predator of T. absoluta eggs, it can also prey on the early host larval instars (1st and 2nd) which are the preferred oviposition host stages of D. gelechiidivoris. Here, the impact of N. tenuis feeding on T. absoluta and the effects on D. gelechiidivoris performance was tested. Regardless of the order of introductions (i.e. the sequence of combination with D. gelechiidivoris) and densities (i.e. number of N. tenuis combined with D. gelechiidivoris), there was no intraguild predation by N. tenuis on D. gelechiidivorisas there was little host larval feeding behaviour. Also, the presence of N. tenuis did not affect the oviposition performance of D. gelechiidivoris. Further investigations revealed that the combined efficacy of N. tenuis and D. gelechiidivorison T. absoluta population was significantly higher than either natural enemy alone, thus contributes to the data supporting the release of D. gelechiidivoris in Africa. In concluding, integrating D. gelechiidivoris and N. tenuis in the management of T. absolut could potentially reduce yield losses in tomato in Eastern Africa where the socio-economic impacts of the pest are very serious.
- Full Text:
- Date Issued: 2021
Prioritising biological control agents for release against Sporobolus pyramidalis and Sporobolus natalensis (Poaceae) in Australia
- Authors: Sutton, Guy Frederick
- Date: 2021
- Subjects: Grasses -- Diseases and pests , Bruchophagus , Wasps , Alien plants -- Biological control -- Australia , Sporobolus -- Biological control -- Africa , Sporobolus -- Biological control -- Australia , Insects as biological pest control agents -- Australia , Insects as biological pest control agents -- Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/172445 , vital:42201 , 10.21504/10962/172445
- Description: Sporobolus pyramidalis Beauv. and S. natalensis (Steud.) Th. Dur. and Schinz. (giant rat’s tail grass) (Poaceae), invade rangelands and pastures in eastern Australia, costing the livestock industry approximately AUS$ 60 million per annum in grazing losses. Mechanical and chemical control options are costly and largely ineffective. Biological control is viewed as the most promising control option, however this management strategy has largely been avoided for grasses, due to their perceived lack of suitably host-specific and damaging natural enemies. In this thesis, the prospects for using biological control against S. pyramidalis and S. natalensis in Australia was assessed, in light of these potential challenges. Climate matching models were used to identify high-priority geographic regions within the plants’ native distributions to survey for potential biological control agents. High-priority regions to perform surveys were identified by modelling the climatic suitability for S. pyramidalis and S. natalensis in sub-Saharan Africa (i.e. their potential native ranges’), and climatic compatibility with regions where biological control is intended in Australia. High-priority regions for S. pyramidalis included: (1) coastal East Africa, ranging from north-eastern South Africa to Uganda, including south-eastern DRC, (2) some parts of West Africa, including inland regions of the Ivory Coast and western Nigeria, (3) northern Angola and (4) eastern Madagascar, and for S. natalensis included: (1) eastern South Africa, (2) eastern Zimbabwe, (3) Burundi, (4) central Ethiopia and (5) central Madagascar. Prospective control agents collected from these regions have the highest probability of establishing and proliferating in Australia, if released. In surveys of the insect assemblages on S. pyramidalis and S. natalensis in the climatically-matched region of eastern South Africa fifteen insect herbivores associated with the grasses were identified. Insect feeding guild, geographic distributions, and seasonal abundances suggest that three stem-boring phytophagous wasps, Tetramesa sp. 1, Tetramesa sp. 2 and Bruchophagus sp. 1 (Hymenoptera: Eurytomidae), have potential as control agents. Species accumulation curves indicated that additional surveys in South Africa are unlikely to yield additional potential control agents. Field host-range surveys of 47 non-target grass species in South Africa showed that Tetramesa sp. 1, Tetramesa sp. 2, and Bruchophagus sp. 1, were only recorded from S. pyramidalis and S. natalensis. Integrating field host-range with phylogenetic relationships between plant species indicated that no native Australian Sporobolus species or economic crops and pastures are expected to be attacked by these wasps. All three wasp species are predicted to be suitably host-specific for release in Australia. Three other endophagous herbivores attacked non-target native African Sporobolus species that share a close phylogenetic relationship to native Australian Sporobolus species, and therefore, demonstrate considerable risk of non-target damage. These species should not be considered as potential control agents. Under native-range, open-field conditions, Tetramesa sp. 1 caused an approximately 5-fold greater reduction in plant survival and reproductive output than Tetramesa sp. 2 and Bruchophagus sp. 1. Tetramesa sp. 1 in combination with Tetramesa sp. 2 did not significantly increase the level of damage, while Bruchophagus sp. 1 may decrease the efficiency of Tetramesa sp. 1, if released in combination. Tetramesa 1 is therefore the most promising candidate agent. Prioritising potential agents using predicted efficacy allowed otherwise equally suitable prospective agents to be prioritised in a strategic manner. Prioritising which natural enemies to target as biological control agents is a complex task. Field host range and damage assessments in the native range may provide more realistic data than typical studies performed under artificial conditions in a laboratory or quarantine. Moreover, it could assist practitioners in prioritising the most suitable agent(s) at the earliest stage in the programme as possible. This study demonstrated that grasses are suitable targets for biological control as they can harbour host-specific and damaging natural enemies.
- Full Text:
- Date Issued: 2021
- Authors: Sutton, Guy Frederick
- Date: 2021
- Subjects: Grasses -- Diseases and pests , Bruchophagus , Wasps , Alien plants -- Biological control -- Australia , Sporobolus -- Biological control -- Africa , Sporobolus -- Biological control -- Australia , Insects as biological pest control agents -- Australia , Insects as biological pest control agents -- Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/172445 , vital:42201 , 10.21504/10962/172445
- Description: Sporobolus pyramidalis Beauv. and S. natalensis (Steud.) Th. Dur. and Schinz. (giant rat’s tail grass) (Poaceae), invade rangelands and pastures in eastern Australia, costing the livestock industry approximately AUS$ 60 million per annum in grazing losses. Mechanical and chemical control options are costly and largely ineffective. Biological control is viewed as the most promising control option, however this management strategy has largely been avoided for grasses, due to their perceived lack of suitably host-specific and damaging natural enemies. In this thesis, the prospects for using biological control against S. pyramidalis and S. natalensis in Australia was assessed, in light of these potential challenges. Climate matching models were used to identify high-priority geographic regions within the plants’ native distributions to survey for potential biological control agents. High-priority regions to perform surveys were identified by modelling the climatic suitability for S. pyramidalis and S. natalensis in sub-Saharan Africa (i.e. their potential native ranges’), and climatic compatibility with regions where biological control is intended in Australia. High-priority regions for S. pyramidalis included: (1) coastal East Africa, ranging from north-eastern South Africa to Uganda, including south-eastern DRC, (2) some parts of West Africa, including inland regions of the Ivory Coast and western Nigeria, (3) northern Angola and (4) eastern Madagascar, and for S. natalensis included: (1) eastern South Africa, (2) eastern Zimbabwe, (3) Burundi, (4) central Ethiopia and (5) central Madagascar. Prospective control agents collected from these regions have the highest probability of establishing and proliferating in Australia, if released. In surveys of the insect assemblages on S. pyramidalis and S. natalensis in the climatically-matched region of eastern South Africa fifteen insect herbivores associated with the grasses were identified. Insect feeding guild, geographic distributions, and seasonal abundances suggest that three stem-boring phytophagous wasps, Tetramesa sp. 1, Tetramesa sp. 2 and Bruchophagus sp. 1 (Hymenoptera: Eurytomidae), have potential as control agents. Species accumulation curves indicated that additional surveys in South Africa are unlikely to yield additional potential control agents. Field host-range surveys of 47 non-target grass species in South Africa showed that Tetramesa sp. 1, Tetramesa sp. 2, and Bruchophagus sp. 1, were only recorded from S. pyramidalis and S. natalensis. Integrating field host-range with phylogenetic relationships between plant species indicated that no native Australian Sporobolus species or economic crops and pastures are expected to be attacked by these wasps. All three wasp species are predicted to be suitably host-specific for release in Australia. Three other endophagous herbivores attacked non-target native African Sporobolus species that share a close phylogenetic relationship to native Australian Sporobolus species, and therefore, demonstrate considerable risk of non-target damage. These species should not be considered as potential control agents. Under native-range, open-field conditions, Tetramesa sp. 1 caused an approximately 5-fold greater reduction in plant survival and reproductive output than Tetramesa sp. 2 and Bruchophagus sp. 1. Tetramesa sp. 1 in combination with Tetramesa sp. 2 did not significantly increase the level of damage, while Bruchophagus sp. 1 may decrease the efficiency of Tetramesa sp. 1, if released in combination. Tetramesa 1 is therefore the most promising candidate agent. Prioritising potential agents using predicted efficacy allowed otherwise equally suitable prospective agents to be prioritised in a strategic manner. Prioritising which natural enemies to target as biological control agents is a complex task. Field host range and damage assessments in the native range may provide more realistic data than typical studies performed under artificial conditions in a laboratory or quarantine. Moreover, it could assist practitioners in prioritising the most suitable agent(s) at the earliest stage in the programme as possible. This study demonstrated that grasses are suitable targets for biological control as they can harbour host-specific and damaging natural enemies.
- Full Text:
- Date Issued: 2021
A genetic analysis of the species and intraspecific lineages of Dactylopius Costa (Hemiptera: Dactylopiidae)
- Van Steenderen, Clarke Julian Mignon
- Authors: Van Steenderen, Clarke Julian Mignon
- Date: 2020
- Subjects: Dactylopius
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/151491 , vital:39135
- Description: The Cactaceae family comprises 15 genera and nearly 2000 species. With one exception, these are all native to the Americas. Numerous cactaceous species are invasive in other parts of the world, resulting in considerable damage to ecosystem functioning and agricultural practices. The most successful biological control agents used to combat invasive Cactaceae belong to the Dactylopius genus (Hemiptera: Dactylopiidae), comprising eleven species. The Dactylopiidae are exclusively cactophagous and are usually host-specific. Some intraspecific lineages of dactylopiids, often referred to as `biotypes', also display host-specificity, and are used to control particular species of invasive Cactaceae. To date, two lineages within Dactylopius opuntiae (`ficus' and `stricta'), and two within D. tomentosus (`cholla' and `imbricata') have been released in South Africa to control Opuntia ficus-indica and O. stricta, and Cylindropuntia fulgida and C. imbricata, respectively. The `californica var. parkeri' lineage is currently under consideration for release in South Africa for the control of C. pallida. Australia has already released these five lineages, and approved the release of an additional three in 2017; namely D. tomentosus `bigelovii', `cylindropuntia sp.', and `acanthocarpa x echinocarpa'. Many of the Dactylopius species are so morphologically similar, and in the case of lineages, identical, that numerous misidentifications have been made in the past. These errors have had serious implications, such as failed attempts at the biological control of cactus weeds. This thesis aimed to generate a multi-locus genetic database to enable the identification of the species and lineages in the Dactylopiidae family, and to test its accuracy. Seven species were included in the analysis, including two lineages within D. opuntiae and six within D. tomentosus. Genetic characterisation was achieved through the DNA sequencing of three gene regions; namely mitochondrial 12S rRNA and cytochrome c oxidase I (COI), nuclear 18S rRNA, and fragment analysis using two inter-simple sequence repeats (ISSRs). Nucleotide sequences were very effective for species-level identification, where the 12S, 18S, and COI regions showed 100%, 94.59%, and 100% identification accuracy rates, respectively. Additionally, the 12S and COI markers distinguished between half of the D. tomentosus lineages (`californica', `cholla', and `imbricata'), with identification accuracies of 100%. The `echinocarpa x acanthocarpa', `bigelovii', and `cylindropuntia sp.' lineages formed one clade. None of the DNA genetic markers showed a separation between the `ficus' and `stricta' lineages within D. opuntiae. Fragment analysis through the use of ISSRs provided higher-resolution results, and addressed this gap by showing a well-supported separation between the two lineages, and between wild populations collected in the Eastern Cape Province in South Africa. The identification accuracy of the `ficus' and `stricta' lineages was 81.82%. This is the first time that a method has been developed that can distinguish between these lineages. An additional component of this thesis was the creation of three user-friendly R-based programs to assist with: 1. ISSR data processing. 2. The identification of query Dactylopius nucleotide sequences relative to the gene databases created here. 3. A graphical user interface (GUI) version of the R package `SPIDER', which is useful for the assessment of the accuracy of genetic barcode data. A successful biological control programme relies on the correct identification of the agent in question, and so it is imperative that cactus biological control practitioners are able to distinguish between Dactylopius species and lineages in order to release the most effective ones onto target Cactaceae. The laboratory protocols reported, and data processing tools created here, have largely addressed this need and offer valuable practical applications. These include: 1. The flagging of potential new species, cryptic species, and lineages of dactylopiid species released as new biocontrol agents. 2. Validating the identifications made by taxonomists based on morphology. 3. Confirming to which species, and, where applicable, to which lineage, a field-collected sample belongs. 4. Identifying hybrids resulting from lineage crosses. Ensuring that the correct Dactylopius species are utilised for biological control will improve the control of invasive Cactaceae and protect biodiversity and agricultural productivity.
- Full Text:
- Date Issued: 2020
- Authors: Van Steenderen, Clarke Julian Mignon
- Date: 2020
- Subjects: Dactylopius
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/151491 , vital:39135
- Description: The Cactaceae family comprises 15 genera and nearly 2000 species. With one exception, these are all native to the Americas. Numerous cactaceous species are invasive in other parts of the world, resulting in considerable damage to ecosystem functioning and agricultural practices. The most successful biological control agents used to combat invasive Cactaceae belong to the Dactylopius genus (Hemiptera: Dactylopiidae), comprising eleven species. The Dactylopiidae are exclusively cactophagous and are usually host-specific. Some intraspecific lineages of dactylopiids, often referred to as `biotypes', also display host-specificity, and are used to control particular species of invasive Cactaceae. To date, two lineages within Dactylopius opuntiae (`ficus' and `stricta'), and two within D. tomentosus (`cholla' and `imbricata') have been released in South Africa to control Opuntia ficus-indica and O. stricta, and Cylindropuntia fulgida and C. imbricata, respectively. The `californica var. parkeri' lineage is currently under consideration for release in South Africa for the control of C. pallida. Australia has already released these five lineages, and approved the release of an additional three in 2017; namely D. tomentosus `bigelovii', `cylindropuntia sp.', and `acanthocarpa x echinocarpa'. Many of the Dactylopius species are so morphologically similar, and in the case of lineages, identical, that numerous misidentifications have been made in the past. These errors have had serious implications, such as failed attempts at the biological control of cactus weeds. This thesis aimed to generate a multi-locus genetic database to enable the identification of the species and lineages in the Dactylopiidae family, and to test its accuracy. Seven species were included in the analysis, including two lineages within D. opuntiae and six within D. tomentosus. Genetic characterisation was achieved through the DNA sequencing of three gene regions; namely mitochondrial 12S rRNA and cytochrome c oxidase I (COI), nuclear 18S rRNA, and fragment analysis using two inter-simple sequence repeats (ISSRs). Nucleotide sequences were very effective for species-level identification, where the 12S, 18S, and COI regions showed 100%, 94.59%, and 100% identification accuracy rates, respectively. Additionally, the 12S and COI markers distinguished between half of the D. tomentosus lineages (`californica', `cholla', and `imbricata'), with identification accuracies of 100%. The `echinocarpa x acanthocarpa', `bigelovii', and `cylindropuntia sp.' lineages formed one clade. None of the DNA genetic markers showed a separation between the `ficus' and `stricta' lineages within D. opuntiae. Fragment analysis through the use of ISSRs provided higher-resolution results, and addressed this gap by showing a well-supported separation between the two lineages, and between wild populations collected in the Eastern Cape Province in South Africa. The identification accuracy of the `ficus' and `stricta' lineages was 81.82%. This is the first time that a method has been developed that can distinguish between these lineages. An additional component of this thesis was the creation of three user-friendly R-based programs to assist with: 1. ISSR data processing. 2. The identification of query Dactylopius nucleotide sequences relative to the gene databases created here. 3. A graphical user interface (GUI) version of the R package `SPIDER', which is useful for the assessment of the accuracy of genetic barcode data. A successful biological control programme relies on the correct identification of the agent in question, and so it is imperative that cactus biological control practitioners are able to distinguish between Dactylopius species and lineages in order to release the most effective ones onto target Cactaceae. The laboratory protocols reported, and data processing tools created here, have largely addressed this need and offer valuable practical applications. These include: 1. The flagging of potential new species, cryptic species, and lineages of dactylopiid species released as new biocontrol agents. 2. Validating the identifications made by taxonomists based on morphology. 3. Confirming to which species, and, where applicable, to which lineage, a field-collected sample belongs. 4. Identifying hybrids resulting from lineage crosses. Ensuring that the correct Dactylopius species are utilised for biological control will improve the control of invasive Cactaceae and protect biodiversity and agricultural productivity.
- Full Text:
- Date Issued: 2020
An initial investigation into biological control options for Schinus terebinthifolia in South Africa
- Magengelele, Nwabisa Laurencia
- Authors: Magengelele, Nwabisa Laurencia
- Date: 2020
- Subjects: Anacardiaceae -- Biological control -- South Africa , Plants, Ornamental -- South Africa , Invasive plants -- Biological control -- South Africa , Insects as biological pest control agents -- South Africa , Brazilian pepper tree -- Biological control -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/103835 , vital:32306
- Description: Schinus terebinthifolia Raddi (Anacardiaceae) (Brazilian pepper tree) is a native tree to subtropical South America that was introduced into South Africa as an ornamental plant. Globally, it is regarded as one of the world’s worst invasive trees. In South Africa, this aggressive pioneer species is becoming increasingly problematic and is being considered as a target for biological control. In South Africa the tree has acquired a native seed-feeding wasp, Megastigmus transvaalensis Hussey (Hymenoptera: Torymidae). The wasp’s native hosts are indigenous Rhus species (Anacardiaceae), but it has expanded its host range to form a new association with both S. terebinthifolia and its close relative S. molle L. (Anacardiaceae). In order to quantify the seed predation by M. transvaalensis on S. terebinthifolia seeds, tree populations were surveyed across the Eastern Cape and KwaZulu-Natal provinces. The wasp was present at 99% of the S. terebinthifolia populations with an average of 22% of the seeds being destroyed. In the Eastern Cape Province, the highest seed damage occurred at the start of the winter months, when about 35% of seeds were damaged. This fell to less than 12% in spring and summer when the plants were flowering. Megastigmus transvaalensis may have slowed the rate of spread of the plant, but it is unlikely to reduce population sizes of S. terebinthifolia in South Africa in the long-term. Biological control efforts can be assisted by knowing the origin and invasion history of the target species. Genetic analyses are often the only way to elucidate the invasion history of invasive alien plants because it is rare to find detailed records of plant introductions. Both microsatellite and chloroplast DNA analysis were conducted on S. terebinthifolia trees from the plant’s introduced distribution in South Africa and both Florida and Hawaii, USA. These samples were compared to plants from the native distribution of South America. The analysis indicated that the S. terebinthifolia in South Africa was most likely sourced from the state of Rio de Janeiro in Brazil, which is the same source of the invasive populations in Florida and Hawaii. Importantly, the South African populations were all found to be “haplotype A”. Plants samples collected from Hawaii USA were the closest match to the South African plants. Biological control agents known to damage haplotype A which have been considered for use in Hawaii and Florida should therefore be prioritised for South Africa. Schinus terebinthifolia has a broad distribution in South Africa; however, the majority of the current distribution is limited to the coastal regions along the eastern coast in KwaZulu-Natal Province. This suggests that the species may be climatically limited. Species distribution models in MaxEnt were used to predict the suitable ecological niche of the species. Using occurrence localities from both the native and invaded range to calibrate the models resulted in 56% of the modelled areas being considered suitable for the growth of S. terebinthifolia in South Africa. This included areas in the Eastern Cape, Western Cape and Limpopo provinces. When the models were calibrated using just the native range data, or just the invaded range data, predicted distributions were more restricted and limited to the coastal areas of the Eastern Cape and KwaZulu-Natal provinces. The coastal areas between Florianopolis and Santos in Brazil were highlighted as the most climatically similar to the invasive populations of S. terebinthifolia in South Africa. These areas should be prioritised if native range surveys for potential biological control agents are conducted in South America. Although the native seed-feeding wasp is damaging to S. terebinthifolia in South Africa, the tree is still not under suitable levels of biological control and is likely to spread and increase in density. New biological control agents are therefore required. Genetic and climatic matching has determined where the most appropriate region to collect new potential biological control agents is. The genetic matching data has also indicated that biological control agents that have been released, or are being considered for release, in Hawaii and Florida, are likely to be suitable for the South African plants because they have been shown to be damaging to ‘haplotype A’. These agents should therefore be the first to be considered for release in South Africa.
- Full Text:
- Date Issued: 2020
An initial investigation into biological control options for Schinus terebinthifolia in South Africa
- Authors: Magengelele, Nwabisa Laurencia
- Date: 2020
- Subjects: Anacardiaceae -- Biological control -- South Africa , Plants, Ornamental -- South Africa , Invasive plants -- Biological control -- South Africa , Insects as biological pest control agents -- South Africa , Brazilian pepper tree -- Biological control -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/103835 , vital:32306
- Description: Schinus terebinthifolia Raddi (Anacardiaceae) (Brazilian pepper tree) is a native tree to subtropical South America that was introduced into South Africa as an ornamental plant. Globally, it is regarded as one of the world’s worst invasive trees. In South Africa, this aggressive pioneer species is becoming increasingly problematic and is being considered as a target for biological control. In South Africa the tree has acquired a native seed-feeding wasp, Megastigmus transvaalensis Hussey (Hymenoptera: Torymidae). The wasp’s native hosts are indigenous Rhus species (Anacardiaceae), but it has expanded its host range to form a new association with both S. terebinthifolia and its close relative S. molle L. (Anacardiaceae). In order to quantify the seed predation by M. transvaalensis on S. terebinthifolia seeds, tree populations were surveyed across the Eastern Cape and KwaZulu-Natal provinces. The wasp was present at 99% of the S. terebinthifolia populations with an average of 22% of the seeds being destroyed. In the Eastern Cape Province, the highest seed damage occurred at the start of the winter months, when about 35% of seeds were damaged. This fell to less than 12% in spring and summer when the plants were flowering. Megastigmus transvaalensis may have slowed the rate of spread of the plant, but it is unlikely to reduce population sizes of S. terebinthifolia in South Africa in the long-term. Biological control efforts can be assisted by knowing the origin and invasion history of the target species. Genetic analyses are often the only way to elucidate the invasion history of invasive alien plants because it is rare to find detailed records of plant introductions. Both microsatellite and chloroplast DNA analysis were conducted on S. terebinthifolia trees from the plant’s introduced distribution in South Africa and both Florida and Hawaii, USA. These samples were compared to plants from the native distribution of South America. The analysis indicated that the S. terebinthifolia in South Africa was most likely sourced from the state of Rio de Janeiro in Brazil, which is the same source of the invasive populations in Florida and Hawaii. Importantly, the South African populations were all found to be “haplotype A”. Plants samples collected from Hawaii USA were the closest match to the South African plants. Biological control agents known to damage haplotype A which have been considered for use in Hawaii and Florida should therefore be prioritised for South Africa. Schinus terebinthifolia has a broad distribution in South Africa; however, the majority of the current distribution is limited to the coastal regions along the eastern coast in KwaZulu-Natal Province. This suggests that the species may be climatically limited. Species distribution models in MaxEnt were used to predict the suitable ecological niche of the species. Using occurrence localities from both the native and invaded range to calibrate the models resulted in 56% of the modelled areas being considered suitable for the growth of S. terebinthifolia in South Africa. This included areas in the Eastern Cape, Western Cape and Limpopo provinces. When the models were calibrated using just the native range data, or just the invaded range data, predicted distributions were more restricted and limited to the coastal areas of the Eastern Cape and KwaZulu-Natal provinces. The coastal areas between Florianopolis and Santos in Brazil were highlighted as the most climatically similar to the invasive populations of S. terebinthifolia in South Africa. These areas should be prioritised if native range surveys for potential biological control agents are conducted in South America. Although the native seed-feeding wasp is damaging to S. terebinthifolia in South Africa, the tree is still not under suitable levels of biological control and is likely to spread and increase in density. New biological control agents are therefore required. Genetic and climatic matching has determined where the most appropriate region to collect new potential biological control agents is. The genetic matching data has also indicated that biological control agents that have been released, or are being considered for release, in Hawaii and Florida, are likely to be suitable for the South African plants because they have been shown to be damaging to ‘haplotype A’. These agents should therefore be the first to be considered for release in South Africa.
- Full Text:
- Date Issued: 2020
An integrative approach to understanding vulnerability of an alpine range-restricted bird to climate warming
- Authors: Oswald, Krista Natasha
- Date: 2020
- Subjects: Passeriformes -- South Africa -- Western Cape , Passeriformes -- Physiology -- South Africa -- Western Cape , Passeriformes -- Behavior -- Climatic factors -- South Africa -- Western Cape , Passeriformes -- Reproduction -- Climatic factors -- South Africa -- Western Cape , Passeriformes -- Dispersal -- South Africa -- Western Cape , Passeriformes -- Food -- South Africa -- Western Cape , Passeriformes -- Nests-- South Africa -- Western Cape , Blue Hill Nature Reserve , Cape Rockjumper -- Climatic factors , Chaetops frenatus
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/148517 , vital:38746
- Description: Understanding species' vulnerability to climate change requires an integrative ecological approach involving, at minimum, physiology, behaviour, reproductive success, and limitations on dispersal. In this thesis I determined potential negative effects of increasing temperatures on behaviour, reproduction, and ability to disperse in an alpine-restricted bird, the Cape Rockjumper Chaetops frenatus ("Rockjumper"). Here I provide a comprehensive ecological set of data for understanding the link between Rockjumper population declines and warming habitats. I tested whether Rockjumper microsite-use at high temperatures resulted in decreased time spent on important behaviours, such as foraging. I found Rockjumpers made increased use of rock-shade as air temperature increased and so spent less time panting, but birds in rock-shade foraged less. Birds may be constrained to foraging in sun at high temperatures to sustain energy or water requirements, despite risks of high thermal load, or else face lost foraging opportunities by remaining in rock-shade. I determined if adult nest attendance and causes of nest failure were related to high temperatures. I filmed nests over two breeding seasons to examine temperature-effects on adult time in nests, provisioning rate, and resultant nestling daily mass gain. The only temperature effect I found was decreased percent daily change in body mass for older nestlings at hotter temperatures. I also examined causes of nest failure over three breeding seasons in relation to nest concealment and habitat openness by observing failure/success. Nests in more open territories (i.e. early post-fire habitat) had greater success, and the main cause of predation came from Boomslang Dispholydus typus. Importantly, the probability of Boomslang predation increased significantly at hotter temperatures. These findings show there may be direct negative effects of increasing temperatures on reproductive success and population recruitment, and so hotter temperature during the breeding season may be at least partly responsible for observed population declines. Lastly, I examined genetic structure of populations across mountain ranges separated from one another by lowland habitat unsuitable for Rockjumpers. I predicted I would find little evidence for dispersal between mountain ranges separated by unsuitable lowland habitat, but instead found Rockjumpers show little evidence for inbreeding. I also found evidence for a past bottleneck event or founder effect, and little overall genetic diversity (possibly as their specialized niche exerts selective pressure). Low diversity may limit Rockjumpers' ability to adapt to a changing environment. Adult physiological and behavioural thresholds to increasing temperatures are often used to create predictions of climate change effects. My past physiological research and current behavioural research suggest no particularly strong evidence that temperature-related population declines are driven by poor physiological capacity to tolerate heat or negative behaviour trade-offs. Instead, my current research shows that understanding negative effects of increasing temperatures may require a more in-depth approach involving investigation of fine-scale ecological interactions. No single one of my chapters provides the insight necessary for understanding Rockjumper population declines at warming temperatures. Instead, I show how an integrative approach may be necessary for assessing species' vulnerability to climate change by examining multiple ecological aspects of a single sentinel species, using an alpine species with a narrow thermal range and highly specialized habitat niche.
- Full Text:
- Date Issued: 2020
- Authors: Oswald, Krista Natasha
- Date: 2020
- Subjects: Passeriformes -- South Africa -- Western Cape , Passeriformes -- Physiology -- South Africa -- Western Cape , Passeriformes -- Behavior -- Climatic factors -- South Africa -- Western Cape , Passeriformes -- Reproduction -- Climatic factors -- South Africa -- Western Cape , Passeriformes -- Dispersal -- South Africa -- Western Cape , Passeriformes -- Food -- South Africa -- Western Cape , Passeriformes -- Nests-- South Africa -- Western Cape , Blue Hill Nature Reserve , Cape Rockjumper -- Climatic factors , Chaetops frenatus
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/148517 , vital:38746
- Description: Understanding species' vulnerability to climate change requires an integrative ecological approach involving, at minimum, physiology, behaviour, reproductive success, and limitations on dispersal. In this thesis I determined potential negative effects of increasing temperatures on behaviour, reproduction, and ability to disperse in an alpine-restricted bird, the Cape Rockjumper Chaetops frenatus ("Rockjumper"). Here I provide a comprehensive ecological set of data for understanding the link between Rockjumper population declines and warming habitats. I tested whether Rockjumper microsite-use at high temperatures resulted in decreased time spent on important behaviours, such as foraging. I found Rockjumpers made increased use of rock-shade as air temperature increased and so spent less time panting, but birds in rock-shade foraged less. Birds may be constrained to foraging in sun at high temperatures to sustain energy or water requirements, despite risks of high thermal load, or else face lost foraging opportunities by remaining in rock-shade. I determined if adult nest attendance and causes of nest failure were related to high temperatures. I filmed nests over two breeding seasons to examine temperature-effects on adult time in nests, provisioning rate, and resultant nestling daily mass gain. The only temperature effect I found was decreased percent daily change in body mass for older nestlings at hotter temperatures. I also examined causes of nest failure over three breeding seasons in relation to nest concealment and habitat openness by observing failure/success. Nests in more open territories (i.e. early post-fire habitat) had greater success, and the main cause of predation came from Boomslang Dispholydus typus. Importantly, the probability of Boomslang predation increased significantly at hotter temperatures. These findings show there may be direct negative effects of increasing temperatures on reproductive success and population recruitment, and so hotter temperature during the breeding season may be at least partly responsible for observed population declines. Lastly, I examined genetic structure of populations across mountain ranges separated from one another by lowland habitat unsuitable for Rockjumpers. I predicted I would find little evidence for dispersal between mountain ranges separated by unsuitable lowland habitat, but instead found Rockjumpers show little evidence for inbreeding. I also found evidence for a past bottleneck event or founder effect, and little overall genetic diversity (possibly as their specialized niche exerts selective pressure). Low diversity may limit Rockjumpers' ability to adapt to a changing environment. Adult physiological and behavioural thresholds to increasing temperatures are often used to create predictions of climate change effects. My past physiological research and current behavioural research suggest no particularly strong evidence that temperature-related population declines are driven by poor physiological capacity to tolerate heat or negative behaviour trade-offs. Instead, my current research shows that understanding negative effects of increasing temperatures may require a more in-depth approach involving investigation of fine-scale ecological interactions. No single one of my chapters provides the insight necessary for understanding Rockjumper population declines at warming temperatures. Instead, I show how an integrative approach may be necessary for assessing species' vulnerability to climate change by examining multiple ecological aspects of a single sentinel species, using an alpine species with a narrow thermal range and highly specialized habitat niche.
- Full Text:
- Date Issued: 2020
Assessing invasive alien aquatic plant species, phytoremediation effects using biological indicators in the Swartkops River system
- Authors: Tshithukhe, Getrude
- Date: 2020
- Subjects: Aquatic weeds -- Biological control -- South Africa -- Eastern Cape , Alien plants -- Biological control -- South Africa -- Eastern Cape , Phytoremediation -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167665 , vital:41501
- Description: Pollution effluents in freshwater ecosystems are becoming increasingly ubiquitous as a result of cumulative anthropogenic activities, such as wastewater treatments works, and industrial, agricultural and mining activities. These activities are more noticeable in urban river atchments where there is greater human population densities and industrial developments. The ecological effects of anthropogenic activities on freshwater ecosystems include: excessive deposition of contaminants such as nutrients, pharmaceuticals, microplastics and other chemicals, which change physicochemical properties, causing a decline in aquatic biodiversity. These effects, impact negatively on the resilience of freshwater, making the systems vulnerable to invasion by alien aquatic plants. Ultimately, the loss of local biodiversity associated with the invasive alien aquatic plants (IAAP) results in a loss of some ecosystem goods and services. The Swartkops River system, Eastern Cape Province, drains most of the neighbouring formal and informal settlements, agricultural lands and industries, and hence is exposed to water pollution from human activities along the river catchment. Various water quality assessments are needed to evaluate the extent of pollutants and their impacts on the river ecosystem. Phytoremediation is one approach employed internationally for removing harmful nutrients and chemicals in freshwater ecosystems. Most studies measure the success of phytoremediation through measuring the reduction of contaminants in water or soil chemistry in mesocosm settings, which may not take into account all the important environmental factors that exist in the field. The present study assesses the phytoremediation potential of Pontederia (Eichhornia) crassipes and Salvinia molesta by evaluating water and sediment chemistry, periphyton and aquatic macroinvertebrate community recovery along seven field sites (excluding IAAP species mats sites) located upstream and downstream IAAP species mats on the Swartkops River between April and September 2018. Water and sediment samples were collected once monthly on ten seven field sites, including the IAAP species mat sites. Periphyton and aquatic macroinvertebrates were collected on seven sites, excluding the IAAP mat sites. Pontederia crassipes and S. molesta infestation in Swartkops River showed positive phytoremediation results and improved some water and sediment chemistry in the downstream treatments as compared to upstream treatments. Although there were some fluctuations with some variables, important water and sediment chemistry were reduced downstream. By contrast, biological assessment results did not show any response to the presence of IAAP species and phytoremediation. Periphyton and aquatic macroinvertebrates diversity and community assemblages were more influenced by water quality. Although IAAP species did provide improvement in water and sediments chemistry, multiple effluent point and non-point sources in Swartkops outpaced phytoremediation. Taxa evenness and relative taxa abundance showed significant differences between the upstream and downstream sites, however taxa richness and Shannon’s diversity showed no significant differences, indicating no relative recovery in biodiversity for either periphyton or aquatic macroinvertebrates. Similarly, the upstream and downstream sites showed similar periphyton and aquatic macroinvertebrates assemblages structure, all dominated by pollution tolerant taxa, thus indicating no functional diversity improvement down river; because of improvement in water chemistry downstream sites, it was expected that periphyton and aquatic macroinvertebrates assemblage structure would also improve at these downstream sites.It is possible that the phytoremediation process is outpaced by effluent discharges, given the multiple sources and distance between upstream and downstream mat sites. The study showed phytoremediation potential but the results were not indicated by biological indicators. A replica study conducted on a moderately disturbed river system is recommended to measure the success and recovery of biological indicators and assemblage composition following IAAP species phytoremediation; a moderately disturbed river compared to a largely disturbed river will broaden findings and look at differences for a wider application of phytoremediation.
- Full Text:
- Date Issued: 2020
- Authors: Tshithukhe, Getrude
- Date: 2020
- Subjects: Aquatic weeds -- Biological control -- South Africa -- Eastern Cape , Alien plants -- Biological control -- South Africa -- Eastern Cape , Phytoremediation -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167665 , vital:41501
- Description: Pollution effluents in freshwater ecosystems are becoming increasingly ubiquitous as a result of cumulative anthropogenic activities, such as wastewater treatments works, and industrial, agricultural and mining activities. These activities are more noticeable in urban river atchments where there is greater human population densities and industrial developments. The ecological effects of anthropogenic activities on freshwater ecosystems include: excessive deposition of contaminants such as nutrients, pharmaceuticals, microplastics and other chemicals, which change physicochemical properties, causing a decline in aquatic biodiversity. These effects, impact negatively on the resilience of freshwater, making the systems vulnerable to invasion by alien aquatic plants. Ultimately, the loss of local biodiversity associated with the invasive alien aquatic plants (IAAP) results in a loss of some ecosystem goods and services. The Swartkops River system, Eastern Cape Province, drains most of the neighbouring formal and informal settlements, agricultural lands and industries, and hence is exposed to water pollution from human activities along the river catchment. Various water quality assessments are needed to evaluate the extent of pollutants and their impacts on the river ecosystem. Phytoremediation is one approach employed internationally for removing harmful nutrients and chemicals in freshwater ecosystems. Most studies measure the success of phytoremediation through measuring the reduction of contaminants in water or soil chemistry in mesocosm settings, which may not take into account all the important environmental factors that exist in the field. The present study assesses the phytoremediation potential of Pontederia (Eichhornia) crassipes and Salvinia molesta by evaluating water and sediment chemistry, periphyton and aquatic macroinvertebrate community recovery along seven field sites (excluding IAAP species mats sites) located upstream and downstream IAAP species mats on the Swartkops River between April and September 2018. Water and sediment samples were collected once monthly on ten seven field sites, including the IAAP species mat sites. Periphyton and aquatic macroinvertebrates were collected on seven sites, excluding the IAAP mat sites. Pontederia crassipes and S. molesta infestation in Swartkops River showed positive phytoremediation results and improved some water and sediment chemistry in the downstream treatments as compared to upstream treatments. Although there were some fluctuations with some variables, important water and sediment chemistry were reduced downstream. By contrast, biological assessment results did not show any response to the presence of IAAP species and phytoremediation. Periphyton and aquatic macroinvertebrates diversity and community assemblages were more influenced by water quality. Although IAAP species did provide improvement in water and sediments chemistry, multiple effluent point and non-point sources in Swartkops outpaced phytoremediation. Taxa evenness and relative taxa abundance showed significant differences between the upstream and downstream sites, however taxa richness and Shannon’s diversity showed no significant differences, indicating no relative recovery in biodiversity for either periphyton or aquatic macroinvertebrates. Similarly, the upstream and downstream sites showed similar periphyton and aquatic macroinvertebrates assemblages structure, all dominated by pollution tolerant taxa, thus indicating no functional diversity improvement down river; because of improvement in water chemistry downstream sites, it was expected that periphyton and aquatic macroinvertebrates assemblage structure would also improve at these downstream sites.It is possible that the phytoremediation process is outpaced by effluent discharges, given the multiple sources and distance between upstream and downstream mat sites. The study showed phytoremediation potential but the results were not indicated by biological indicators. A replica study conducted on a moderately disturbed river system is recommended to measure the success and recovery of biological indicators and assemblage composition following IAAP species phytoremediation; a moderately disturbed river compared to a largely disturbed river will broaden findings and look at differences for a wider application of phytoremediation.
- Full Text:
- Date Issued: 2020
Biogeographic patterns of endolithic cyanobacteria and their negative impacts on mussels along the South African coast
- Authors: Ndhlovu, Aldwin
- Date: 2020
- Subjects: Cyanobacteria -- South Africa , Cyanobacteria -- Geographical distribution , Prokaryotes -- South Africa , Mexilhao mussel -- South Africa , Mytilus galloprovincialis -- South Africa , Coastal biology -- South Africa , Coastal ecology -- South Africa , Mussels -- Geographical distribution , Mussels -- Predators of , Mussels -- Mortality -- South Africa , Mussels -- Ecology -- South Africa , Mussels -- Growth -- South Africa , Mussels -- Fertility -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/144656 , vital:38367
- Description: Endolithic cyanobacterial species occur in a wide range of environments including cold and hot deserts as well as marine systems where they attack biological material such as corals and the shells of molluscs including limpets, mussels and abalone. Endoliths live as parasites in mussel shells, where they erode and extract calcium carbonate leading to shell weakening, creating fracture holes that lead to shell collapse and death, but they also have positive effects when they lead to discolouration of mussel shells hence giving them the ability to reduce stressful heat gain during periods of extreme heat stress. Mussels are ecological engineers on which the abundance and diversity of associated species assemblages depend. Understanding how endolithic cyanobacteria affect mussels will not only help in predicting future patterns of mussel abundances, but also future patterns of the infauna that depend on them. Firstly, I identified endolithic species infesting mussels and assessed the prevalence of endolithic parasitism in two intertidal mussel species in South Africa, the native Perna perna and the invasive Mytilus galloprovincialis. Large-scale surveys of endolithic infestation of mussels were conducted along 2500 km of the South African coast, covering three biogeographic regions: the subtropical east coast, dominated by P. perna, the warm temperate south coast where the indigenous species coexists with M. galloprovincialis, and the cool temperate west coast which is dominated by M. galloprovincialis. The prevalence of endolithic infestation was higher in the cool temperate bioregion than in the warm temperate and subtropical bioregions which did not differ and for P. perna endolithic species assemblages revealed clear groupings by bioregion. Results for endolithic induced mortality followed the same trend, with no significant difference between the two mussel species where they coexist and these results attribute biogeography of endoliths to environmental factors rather than host identity. Secondly, I assessed energy budgets of infested and clean mussels, to evaluate the energetic cost of infestation. This involved measuring energy acquisition, expenditure, calculating scope for growth and lethal temperatures (LT50s). The results revealed that endolithic cyanobacteria have a negative effect on scope for growth due to increased metabolic rates for infested mussels, with no effect of endoliths on the rates or efficiency of energy acquisition through filtration and no effect on lethal temperatures. The effects of infestation were then examined in more detail through a qualitative and quantitative analysis of mussel gonads and byssal attachment strength to the substratum. Endolithic infestation was found to affect reproduction by affecting the size (mass) of gonads, but not the density of eggs within them. Attachment strength was affected by endolithic infestation with very infested mussels requiring much less force to detach them from the substratum compared to mussels with low or no infestation. These results show that endolithic infestation affects mussel fitness by directly affecting attachment strength and by reducing their reproductive output. Thirdly, endolithic succession within mussel shells was examined by assessing endolithic species composition in different regions of the shell and as a function of time. The results on the spatial distribution of endolith species within a shell supported those for temporal succession in shells deployed in the field. Endolithic species that were early colonists of clean shells were similar to those that were found in the distal edge, the new and growing region of the shell and species that arrived late in succession were similar to endolithic species found near the umbo, the oldest region of the shell. Overall, the study shows that endolithic cyanobacteria show the effects of biogeography on species distribution and clear patterns of succession within mussel shells. Cyanobacteria affect mussels negatively; they lead to low scope for growth and hence low growth rates, low reproductive output and reduced attachment strength for infested mussels. This, in turn is expected to have indirect consequences for other species that rely on mussels as ecological engineers for their survival.
- Full Text:
- Date Issued: 2020
- Authors: Ndhlovu, Aldwin
- Date: 2020
- Subjects: Cyanobacteria -- South Africa , Cyanobacteria -- Geographical distribution , Prokaryotes -- South Africa , Mexilhao mussel -- South Africa , Mytilus galloprovincialis -- South Africa , Coastal biology -- South Africa , Coastal ecology -- South Africa , Mussels -- Geographical distribution , Mussels -- Predators of , Mussels -- Mortality -- South Africa , Mussels -- Ecology -- South Africa , Mussels -- Growth -- South Africa , Mussels -- Fertility -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/144656 , vital:38367
- Description: Endolithic cyanobacterial species occur in a wide range of environments including cold and hot deserts as well as marine systems where they attack biological material such as corals and the shells of molluscs including limpets, mussels and abalone. Endoliths live as parasites in mussel shells, where they erode and extract calcium carbonate leading to shell weakening, creating fracture holes that lead to shell collapse and death, but they also have positive effects when they lead to discolouration of mussel shells hence giving them the ability to reduce stressful heat gain during periods of extreme heat stress. Mussels are ecological engineers on which the abundance and diversity of associated species assemblages depend. Understanding how endolithic cyanobacteria affect mussels will not only help in predicting future patterns of mussel abundances, but also future patterns of the infauna that depend on them. Firstly, I identified endolithic species infesting mussels and assessed the prevalence of endolithic parasitism in two intertidal mussel species in South Africa, the native Perna perna and the invasive Mytilus galloprovincialis. Large-scale surveys of endolithic infestation of mussels were conducted along 2500 km of the South African coast, covering three biogeographic regions: the subtropical east coast, dominated by P. perna, the warm temperate south coast where the indigenous species coexists with M. galloprovincialis, and the cool temperate west coast which is dominated by M. galloprovincialis. The prevalence of endolithic infestation was higher in the cool temperate bioregion than in the warm temperate and subtropical bioregions which did not differ and for P. perna endolithic species assemblages revealed clear groupings by bioregion. Results for endolithic induced mortality followed the same trend, with no significant difference between the two mussel species where they coexist and these results attribute biogeography of endoliths to environmental factors rather than host identity. Secondly, I assessed energy budgets of infested and clean mussels, to evaluate the energetic cost of infestation. This involved measuring energy acquisition, expenditure, calculating scope for growth and lethal temperatures (LT50s). The results revealed that endolithic cyanobacteria have a negative effect on scope for growth due to increased metabolic rates for infested mussels, with no effect of endoliths on the rates or efficiency of energy acquisition through filtration and no effect on lethal temperatures. The effects of infestation were then examined in more detail through a qualitative and quantitative analysis of mussel gonads and byssal attachment strength to the substratum. Endolithic infestation was found to affect reproduction by affecting the size (mass) of gonads, but not the density of eggs within them. Attachment strength was affected by endolithic infestation with very infested mussels requiring much less force to detach them from the substratum compared to mussels with low or no infestation. These results show that endolithic infestation affects mussel fitness by directly affecting attachment strength and by reducing their reproductive output. Thirdly, endolithic succession within mussel shells was examined by assessing endolithic species composition in different regions of the shell and as a function of time. The results on the spatial distribution of endolith species within a shell supported those for temporal succession in shells deployed in the field. Endolithic species that were early colonists of clean shells were similar to those that were found in the distal edge, the new and growing region of the shell and species that arrived late in succession were similar to endolithic species found near the umbo, the oldest region of the shell. Overall, the study shows that endolithic cyanobacteria show the effects of biogeography on species distribution and clear patterns of succession within mussel shells. Cyanobacteria affect mussels negatively; they lead to low scope for growth and hence low growth rates, low reproductive output and reduced attachment strength for infested mussels. This, in turn is expected to have indirect consequences for other species that rely on mussels as ecological engineers for their survival.
- Full Text:
- Date Issued: 2020
Carnivore intra-guild competition in Selati Game Reserve, Limpopo Province, South Africa
- Authors: Comley, Jessica
- Date: 2020
- Subjects: Hyenas -- Behavior -- South Africa , Hyenas -- South Africa , Hyenas -- Ecology -- South Africa , Top predators -- South Africa , Top predators -- Ecology -- South Africa , Animal communities -- South Africa , Animal behavior -- South Africa , Mutualism (Biology) -- South Africa , Coexistence of species -- South Africa , Game farms -- South Africa , Selati Game Reserve (South Africa)
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/115558 , vital:34163
- Description: Carnivore intra-guild interactions can be important drivers of carnivore community composition and ecosystem functioning. Large carnivores are particularly important since they occupy the highest trophic levels and can exert extensive influences on subordinate carnivores and prey species. Given Africa’s rapidly expanding human population, enclosed reserves such as those found in South Africa, may become increasingly important for carnivore conservation. A major concern, however, is that the interactions and co-existence of multiple carnivores in these systems is poorly understood. Additionally, the majority of reserves in South Africa are small ( 400km²), potentially increasing the likelihood of competition. My research aimed to provide insight into the interactions and co-existence of a multi-carnivore community within a small, enclosed reserve in South Africa (Selati Game Reserve). I tackled this task by using a combination of field techniques including camera trap surveys, ungulate transect surveys, aerial count surveys, location data collected from collared large carnivores and scat and kill site analyses. I found that carnivore-carnivore interactions, and their associated impacts, varied within the carnivore guild and that co-existence may be due to trade-offs between various risks (i.e. interference and exploitative competition) and benefits (i.e. resources such as food and space). My findings also revealed that large carnivores, such as lions (Panthera leo), spotted hyaenas (Crocuta crocuta) and leopards (Panthera pardus) do not have homogenous effects and that site-specific research on multiple-carnivores is integral for conserving biodiversity and ecosystem dynamics. Lions were the dominant large carnivore (in terms of intra-guild predation, space use and resource use) despite being outnumbered seven to one by spotted hyaenas. Leopard occupancy was negatively influenced by lions and leopard diet overlapped almost completely (91%) with spotted hyaenas, suggesting increased kleptoparasitism of leopard kills by spotted hyaenas. While my study provides valuable insight into the complexity of carnivore intra-guild competition in a small, enclosed reserve it also highlights major research gaps and emphasises the need for ecosystem-based research throughout southern Africa to fully understand how multiple sympatric carnivores co-exist in these systems.
- Full Text:
- Date Issued: 2020
- Authors: Comley, Jessica
- Date: 2020
- Subjects: Hyenas -- Behavior -- South Africa , Hyenas -- South Africa , Hyenas -- Ecology -- South Africa , Top predators -- South Africa , Top predators -- Ecology -- South Africa , Animal communities -- South Africa , Animal behavior -- South Africa , Mutualism (Biology) -- South Africa , Coexistence of species -- South Africa , Game farms -- South Africa , Selati Game Reserve (South Africa)
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/115558 , vital:34163
- Description: Carnivore intra-guild interactions can be important drivers of carnivore community composition and ecosystem functioning. Large carnivores are particularly important since they occupy the highest trophic levels and can exert extensive influences on subordinate carnivores and prey species. Given Africa’s rapidly expanding human population, enclosed reserves such as those found in South Africa, may become increasingly important for carnivore conservation. A major concern, however, is that the interactions and co-existence of multiple carnivores in these systems is poorly understood. Additionally, the majority of reserves in South Africa are small ( 400km²), potentially increasing the likelihood of competition. My research aimed to provide insight into the interactions and co-existence of a multi-carnivore community within a small, enclosed reserve in South Africa (Selati Game Reserve). I tackled this task by using a combination of field techniques including camera trap surveys, ungulate transect surveys, aerial count surveys, location data collected from collared large carnivores and scat and kill site analyses. I found that carnivore-carnivore interactions, and their associated impacts, varied within the carnivore guild and that co-existence may be due to trade-offs between various risks (i.e. interference and exploitative competition) and benefits (i.e. resources such as food and space). My findings also revealed that large carnivores, such as lions (Panthera leo), spotted hyaenas (Crocuta crocuta) and leopards (Panthera pardus) do not have homogenous effects and that site-specific research on multiple-carnivores is integral for conserving biodiversity and ecosystem dynamics. Lions were the dominant large carnivore (in terms of intra-guild predation, space use and resource use) despite being outnumbered seven to one by spotted hyaenas. Leopard occupancy was negatively influenced by lions and leopard diet overlapped almost completely (91%) with spotted hyaenas, suggesting increased kleptoparasitism of leopard kills by spotted hyaenas. While my study provides valuable insight into the complexity of carnivore intra-guild competition in a small, enclosed reserve it also highlights major research gaps and emphasises the need for ecosystem-based research throughout southern Africa to fully understand how multiple sympatric carnivores co-exist in these systems.
- Full Text:
- Date Issued: 2020
Combining DNA barcoding and morphology to identify larval fishes from the nearshore environment off the south-east coast of South Africa
- Authors: Somana, Zinzi Sinazo
- Date: 2020
- Subjects: Fishes -- Larvae -- South Africa -- Identification , Fishes -- Genetics -- Research -- Technique , Fishes -- South Africa -- Classification , Genetic markers
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/144605 , vital:38362
- Description: The early life history stages of most marine fish species are undescribed. The problem is, most of these fishes have pelagic larvae which are minute, delicate forms. Linking the larval stage to an adult counterpart is extremely challenging as larvae are morphologically different from the adults. Historically, larval fish identification relied solely on distinguishing morphological characteristics and meristic measurements, which has resulted in taxonomic confusion and misidentification. The introduction of the deoxyribonucleic acid (DNA) barcoding technique as an alternative approach has been successful in positively identifying larval fishes. The correct identification of larval specimens is the key to a better understanding of larval ecology, which underpins the success of any adult fish population. This study aimed to positively identify larval fishes of the south-east coast of South Africa using morphological characteristics and DNA barcoding. Larval and eggs specimens for this study were collected from the shallow nearshore waters of the south-east coast of South Africa. A total of 177 larval specimens were used for morphological analysis. Body shape, gut shape, pigmentation and morphometric measurements (such as body depth, preanal length and total body length) were used to identify each specimen to the family level. In addition, a fragment of mitochondrial cytochrome c oxidase subunit 1 gene (COI) was adopted for sequencing to identify larval fish specimens and fish eggs. Sequences generated from this study were compared to those in the Barcode of Life Database (BOLD). When there were no close matches to a sequence, the GenBank nucleic acid sequence database, maintained by the National Center for Biotechnology Information (NCBI), was used as an alternative. A total of 18 different families were identified through morphology. Seventy-seven of the 177 larval specimens were not subjected to morphological identification due to physical damage. The majority of larvae identified using morphological characteristics belonged to either the Sparidae, Tripterygiidae or Gobiesocidae fish families. Through DNA barcoding, 12 fish families, 16 genera and 18 different species were identified. Ten DNA barcodes (categorised as ‘no match’) from 10 different larval specimens were not identified through any of the online databases. Therefore, the 2% threshold value was used to identify members of the same species. The K2P genetic distance relationships were calculated among the no match sequences and downloaded probability matches from NCBI. This resulted in two unknown specimens assigned to the Blenniidae and Gobiidae. All other taxa were identified to species level, except specimens representing the Gobiidae and Tripterygiidae families. Based on the K2P genetic distances Gobiidae representatives were categorised as members of the Caffrogobius genus. Twenty-eight barcodes represented specimens from the Tripterygiidae. DNA barcode data from COI was analysed using the standard phylogenetic procedures in MEGA6 to examine relationships and differentiation among sequences. These could not be identified to the lowest taxonomic rank due to limited sequence data to compare them with. The sequence data from these specimens gave different results in the two online databases. BOLD results were to family level (Tripterygiidae) and NCBI to the species level (Clinidae: Pavoclinus profundus). Results in this study confirmed the efficiency of the DNA barcoding technique in species level identification of fish larvae. The evidence from genetic barcodes of the Tripterygiidae specimens, supported by morphological characteristics, suggests the need for thorough research to identify the individuals to the species level. The fact that this study identified taxonomically problematic Gobiidae and Tripterygiidae specimens suggests that studies similar to this may highlight additional diversity and help to resolve the taxonomy of other species in these families. However, the lack of reference sequence data from the adult specimens, and especially those with cryptic diversity, were both shortcomings for the positive identification of larvae. With that being said, it shows the necessity for more research to be conducted on barcoding of larvae in general as to accommodate all kinds of species from biodiversity to economic perspectives.
- Full Text:
- Date Issued: 2020
- Authors: Somana, Zinzi Sinazo
- Date: 2020
- Subjects: Fishes -- Larvae -- South Africa -- Identification , Fishes -- Genetics -- Research -- Technique , Fishes -- South Africa -- Classification , Genetic markers
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/144605 , vital:38362
- Description: The early life history stages of most marine fish species are undescribed. The problem is, most of these fishes have pelagic larvae which are minute, delicate forms. Linking the larval stage to an adult counterpart is extremely challenging as larvae are morphologically different from the adults. Historically, larval fish identification relied solely on distinguishing morphological characteristics and meristic measurements, which has resulted in taxonomic confusion and misidentification. The introduction of the deoxyribonucleic acid (DNA) barcoding technique as an alternative approach has been successful in positively identifying larval fishes. The correct identification of larval specimens is the key to a better understanding of larval ecology, which underpins the success of any adult fish population. This study aimed to positively identify larval fishes of the south-east coast of South Africa using morphological characteristics and DNA barcoding. Larval and eggs specimens for this study were collected from the shallow nearshore waters of the south-east coast of South Africa. A total of 177 larval specimens were used for morphological analysis. Body shape, gut shape, pigmentation and morphometric measurements (such as body depth, preanal length and total body length) were used to identify each specimen to the family level. In addition, a fragment of mitochondrial cytochrome c oxidase subunit 1 gene (COI) was adopted for sequencing to identify larval fish specimens and fish eggs. Sequences generated from this study were compared to those in the Barcode of Life Database (BOLD). When there were no close matches to a sequence, the GenBank nucleic acid sequence database, maintained by the National Center for Biotechnology Information (NCBI), was used as an alternative. A total of 18 different families were identified through morphology. Seventy-seven of the 177 larval specimens were not subjected to morphological identification due to physical damage. The majority of larvae identified using morphological characteristics belonged to either the Sparidae, Tripterygiidae or Gobiesocidae fish families. Through DNA barcoding, 12 fish families, 16 genera and 18 different species were identified. Ten DNA barcodes (categorised as ‘no match’) from 10 different larval specimens were not identified through any of the online databases. Therefore, the 2% threshold value was used to identify members of the same species. The K2P genetic distance relationships were calculated among the no match sequences and downloaded probability matches from NCBI. This resulted in two unknown specimens assigned to the Blenniidae and Gobiidae. All other taxa were identified to species level, except specimens representing the Gobiidae and Tripterygiidae families. Based on the K2P genetic distances Gobiidae representatives were categorised as members of the Caffrogobius genus. Twenty-eight barcodes represented specimens from the Tripterygiidae. DNA barcode data from COI was analysed using the standard phylogenetic procedures in MEGA6 to examine relationships and differentiation among sequences. These could not be identified to the lowest taxonomic rank due to limited sequence data to compare them with. The sequence data from these specimens gave different results in the two online databases. BOLD results were to family level (Tripterygiidae) and NCBI to the species level (Clinidae: Pavoclinus profundus). Results in this study confirmed the efficiency of the DNA barcoding technique in species level identification of fish larvae. The evidence from genetic barcodes of the Tripterygiidae specimens, supported by morphological characteristics, suggests the need for thorough research to identify the individuals to the species level. The fact that this study identified taxonomically problematic Gobiidae and Tripterygiidae specimens suggests that studies similar to this may highlight additional diversity and help to resolve the taxonomy of other species in these families. However, the lack of reference sequence data from the adult specimens, and especially those with cryptic diversity, were both shortcomings for the positive identification of larvae. With that being said, it shows the necessity for more research to be conducted on barcoding of larvae in general as to accommodate all kinds of species from biodiversity to economic perspectives.
- Full Text:
- Date Issued: 2020
Ecological assessment of a temperate river system using biomonitoring techniques: a case study of the Bloukrans River system, South Africa
- Authors: Magadze, Tinotenda
- Date: 2020
- Subjects: Bloukrans River , Ecological assessment (Biology) -- South Africa , Stream ecology -- South Africa , Rivers -- Environmental aspects -- South Africa , Benthic animals -- Effect of human beings on -- South Africa , Water quality biological assessment -- South Africa , Diatoms -- South Africa -- Data processing
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/142933 , vital:38177
- Description: Escalating pressures from growing human populations and environmental impacts increasingly imperil freshwater ecosystems. The Bloukrans River, which drains an urbanised and agricultural catchment in the Eastern Cape province of South Africa, is no exception. Detailed knowledge of the structure and function of the aquatic ecosystems is required in order to create models and matrices that predict, guide assessment and direct intervention on ecological integrity and water quality management in these systems. The main objectives of this research were to: examine the effects of urbanization on the benthic macroinvertebrate functional feeding guild structure among different stream orders; determine if benthic diatoms can be used as effective and reliable indicators of ionic composition and conductivity in different stream order categories and finally; to evaluate the applicability of the South African Diatom Index (SADI) and other indices in the Eastern Cape region of South Africa. Field studies were carried out to explore temporal patterns in community structure (macroinvertebrates and diatoms) and ecosystem function related to land-use patterns, instream habitat availability, and water quality parameters in the Bloukrans River system across four study periods: February (summer) and July (winter) 2016 and February (summer) and May/July (winter) 2018. The study was conducted along a gradient of impacts from less impacted agricultural headwaters to highly impacted urban sites located immediately downstream of the city of Makhanda. Macroinvertebrates were separated into functional feeding groups (FFGs) (i.e. collector-gatherer, collector-filterer, scraper, shredder, and predator) which were then used to assess the effects of selected physico-chemical variables and riparian zone condition on FFG organization. Collector-gatherers were the most abundant in the Bloukrans River and represented 71.3 % of the macroinvertebrate assemblages. Stream order 1species such as Nitzschia palea, Gomphonema parvulum, Tryblionella apiculata, Diploneis vulgaris and Staurosira elliptica. Multivariate analysis (Canonical correspondence analysis (CCA)) indicated that differences in diatom community assemblages were best explained by calcium, magnesium, pH, phosphate, nitrate, dissolved oxygen, sediment nitrate, conductivity and salinity. These results indicate that diatoms can be used as bioindicators for monitoring highly impacted river systems and to also further examine pollution gradients and impacts of specific/point pollution sources. In order to further test the application of diatom indices, nine sites with contrasting water quality were sampled along the length river system in February, May and July 2018. Diatom-based indices incorporated in OMNIDIA software were applied to assess the integrity of the water quality as indicated by diatom communities. For comparative purposes, several foreign indices (e.g. the trophic diatom index (TDI), the percentage pollution-tolerant valves (%PTV), biological diatom index (BDI)) and the South African Diatom Index (SADI) were used in the study. From the results, the Percentage Pollution-Tolerant Valves (%PTV) of most urban sites in the Bloukrans River was above the 20% limit indicating the presence of organic pollutants. Although the foreign diatom indices were applicable in the study, the SADI had significant correlations with most water quality variables (p < 0.05) compared to other indices such as Watanabe Index (WAT), Biological Index of Water Quality Trophic Index (BIWQ) and Trophic Index (TI)). These results support wider use of the SADI as an indicator of water quality conditions in South African river systems. Finally, the observed variations in diatom community structure and composition as a result of changes in water quality were broadly in agreement with the results of macroinvertebrate FFG structure indicating that the two biological indicators can, and should, be used as complementary techniques in the biomonitoring of rivers and streams in South Africa.
- Full Text:
- Date Issued: 2020
- Authors: Magadze, Tinotenda
- Date: 2020
- Subjects: Bloukrans River , Ecological assessment (Biology) -- South Africa , Stream ecology -- South Africa , Rivers -- Environmental aspects -- South Africa , Benthic animals -- Effect of human beings on -- South Africa , Water quality biological assessment -- South Africa , Diatoms -- South Africa -- Data processing
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/142933 , vital:38177
- Description: Escalating pressures from growing human populations and environmental impacts increasingly imperil freshwater ecosystems. The Bloukrans River, which drains an urbanised and agricultural catchment in the Eastern Cape province of South Africa, is no exception. Detailed knowledge of the structure and function of the aquatic ecosystems is required in order to create models and matrices that predict, guide assessment and direct intervention on ecological integrity and water quality management in these systems. The main objectives of this research were to: examine the effects of urbanization on the benthic macroinvertebrate functional feeding guild structure among different stream orders; determine if benthic diatoms can be used as effective and reliable indicators of ionic composition and conductivity in different stream order categories and finally; to evaluate the applicability of the South African Diatom Index (SADI) and other indices in the Eastern Cape region of South Africa. Field studies were carried out to explore temporal patterns in community structure (macroinvertebrates and diatoms) and ecosystem function related to land-use patterns, instream habitat availability, and water quality parameters in the Bloukrans River system across four study periods: February (summer) and July (winter) 2016 and February (summer) and May/July (winter) 2018. The study was conducted along a gradient of impacts from less impacted agricultural headwaters to highly impacted urban sites located immediately downstream of the city of Makhanda. Macroinvertebrates were separated into functional feeding groups (FFGs) (i.e. collector-gatherer, collector-filterer, scraper, shredder, and predator) which were then used to assess the effects of selected physico-chemical variables and riparian zone condition on FFG organization. Collector-gatherers were the most abundant in the Bloukrans River and represented 71.3 % of the macroinvertebrate assemblages. Stream order 1species such as Nitzschia palea, Gomphonema parvulum, Tryblionella apiculata, Diploneis vulgaris and Staurosira elliptica. Multivariate analysis (Canonical correspondence analysis (CCA)) indicated that differences in diatom community assemblages were best explained by calcium, magnesium, pH, phosphate, nitrate, dissolved oxygen, sediment nitrate, conductivity and salinity. These results indicate that diatoms can be used as bioindicators for monitoring highly impacted river systems and to also further examine pollution gradients and impacts of specific/point pollution sources. In order to further test the application of diatom indices, nine sites with contrasting water quality were sampled along the length river system in February, May and July 2018. Diatom-based indices incorporated in OMNIDIA software were applied to assess the integrity of the water quality as indicated by diatom communities. For comparative purposes, several foreign indices (e.g. the trophic diatom index (TDI), the percentage pollution-tolerant valves (%PTV), biological diatom index (BDI)) and the South African Diatom Index (SADI) were used in the study. From the results, the Percentage Pollution-Tolerant Valves (%PTV) of most urban sites in the Bloukrans River was above the 20% limit indicating the presence of organic pollutants. Although the foreign diatom indices were applicable in the study, the SADI had significant correlations with most water quality variables (p < 0.05) compared to other indices such as Watanabe Index (WAT), Biological Index of Water Quality Trophic Index (BIWQ) and Trophic Index (TI)). These results support wider use of the SADI as an indicator of water quality conditions in South African river systems. Finally, the observed variations in diatom community structure and composition as a result of changes in water quality were broadly in agreement with the results of macroinvertebrate FFG structure indicating that the two biological indicators can, and should, be used as complementary techniques in the biomonitoring of rivers and streams in South Africa.
- Full Text:
- Date Issued: 2020
Ecological engineering: an assessment of the ecological impact of Reno mattress structures used in erosion control in the Keurbooms Estuary, South Africa
- Authors: De Villiers, Nina
- Date: 2020
- Subjects: Sediments (Geology) -- Management , Sediments (Geology) -- South Africa -- Keurboomstrand , Coast changes -- South Africa -- Keurboomstrand , Shore protection -- South Africa -- Keurboomstrand , Coastal engineering-- South Africa -- Keurboomstrand , Coastal zone management-- South Africa -- Keurboomstrand , Estuarine ecology-- South Africa -- Keurboomstrand , Eelgrass -- South Africa -- Keurboomstrand , Reno Mattresses
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/166138 , vital:41332
- Description: Global climate changes have been associated with ocean warming and sea-level rise. Armouring of coastlines has become common practice with the increasing threat of coastal erosion. The transformation of soft sediment habitats to hard, artificial habitats because of coastline armouring can lead to changes in species diversity, composition and distribution. It is, therefore, essential to assess changes to habitats from coastal development as well as the ecological impact erosion control structures have within coastal systems. Ecological engineering attempts to combine engineering principals and ecological processes to reduce environmental impacts from coastal development and the implementation of artificial structures. Estuaries are particularly vulnerable to anthropogenic impacts through development, and are extremely important systems offering nursery and foraging grounds for many species. These systems are, however, particularly vulnerable to anthropogenic impacts from urbanisation and development. Within South Africa many estuaries are being transformed by the addition of artificial structures to combat erosion, one such structure is the Reno mattress (a flattened wire box filled with rocks). This study compared the fish diversity and abundances of existing Reno mattress structures and natural eelgrass (Zostera capensis) habitat in the Keurbooms Estuary, South Africa. Benthic invertebrates were sampled using standard core sampling and an adapted suction sampling approach within the two habitats. The non-destructive method of mini Baited Remote Underwater Video Systems (BRUVs) was used to sample fish. Seasonal benthic invertebrate and fish abundances and assemblages were assessed from winter 2018 to spring 2019 with greater abundances of both recorded in summer. Significantly greater abundances, diversity, and richness of fish were found in the Reno mattress habitat compared to Z. capensis. Invertebrate taxa displayed some overlap between habitats, however, three higher taxonomic groups were only recorded within Reno mattress habitat and one only within the eelgrass habitat. Fish assemblages differed significantly between the two established habitats. A Before-After-Control-Impact (BACI) investigation was used to assess the ecological impact of newly installed Reno mattresses in the Keurbooms Estuary. Zostera capensis extent was sampled by determining the percentage cover of 0.5 m X 0.5 m quadrats and measurements of eelgrass blades. Percentage cover and blade length decreased during the installation of Reno mattress, but then recovered shortly after completion of the installation. Abundances, richness and diversity of invertebrates and fish were found to be similar before and after the installation which suggests that the installation had no net negative impact on the site. The Reno mattresses were found to attract fauna typical of rocky shore environments as well as a few invasive alien invertebrate species. This study noted that a hybrid habitat of Reno mattress and eelgrass was created and may in fact provide the positives of both to a system. In any coastal development it will be important to balance the demands of a growing population and the protection of natural habitats. The results of this study suggest that complex artificial structures such as Reno mattresses do provide habitat for fish and invertebrates. However, the use of these structures should be in combination with natural vegetation (e.g. as a hybrid habitat) and not one that replaces intertidal and subtidal natural habitat especially eelgrass. There is limited information regarding the ecological impacts of using Reno mattresses in estuaries and this study provides new information on their ecological efficacy that should be valuable for future coastal erosion control practices.
- Full Text:
- Date Issued: 2020
- Authors: De Villiers, Nina
- Date: 2020
- Subjects: Sediments (Geology) -- Management , Sediments (Geology) -- South Africa -- Keurboomstrand , Coast changes -- South Africa -- Keurboomstrand , Shore protection -- South Africa -- Keurboomstrand , Coastal engineering-- South Africa -- Keurboomstrand , Coastal zone management-- South Africa -- Keurboomstrand , Estuarine ecology-- South Africa -- Keurboomstrand , Eelgrass -- South Africa -- Keurboomstrand , Reno Mattresses
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/166138 , vital:41332
- Description: Global climate changes have been associated with ocean warming and sea-level rise. Armouring of coastlines has become common practice with the increasing threat of coastal erosion. The transformation of soft sediment habitats to hard, artificial habitats because of coastline armouring can lead to changes in species diversity, composition and distribution. It is, therefore, essential to assess changes to habitats from coastal development as well as the ecological impact erosion control structures have within coastal systems. Ecological engineering attempts to combine engineering principals and ecological processes to reduce environmental impacts from coastal development and the implementation of artificial structures. Estuaries are particularly vulnerable to anthropogenic impacts through development, and are extremely important systems offering nursery and foraging grounds for many species. These systems are, however, particularly vulnerable to anthropogenic impacts from urbanisation and development. Within South Africa many estuaries are being transformed by the addition of artificial structures to combat erosion, one such structure is the Reno mattress (a flattened wire box filled with rocks). This study compared the fish diversity and abundances of existing Reno mattress structures and natural eelgrass (Zostera capensis) habitat in the Keurbooms Estuary, South Africa. Benthic invertebrates were sampled using standard core sampling and an adapted suction sampling approach within the two habitats. The non-destructive method of mini Baited Remote Underwater Video Systems (BRUVs) was used to sample fish. Seasonal benthic invertebrate and fish abundances and assemblages were assessed from winter 2018 to spring 2019 with greater abundances of both recorded in summer. Significantly greater abundances, diversity, and richness of fish were found in the Reno mattress habitat compared to Z. capensis. Invertebrate taxa displayed some overlap between habitats, however, three higher taxonomic groups were only recorded within Reno mattress habitat and one only within the eelgrass habitat. Fish assemblages differed significantly between the two established habitats. A Before-After-Control-Impact (BACI) investigation was used to assess the ecological impact of newly installed Reno mattresses in the Keurbooms Estuary. Zostera capensis extent was sampled by determining the percentage cover of 0.5 m X 0.5 m quadrats and measurements of eelgrass blades. Percentage cover and blade length decreased during the installation of Reno mattress, but then recovered shortly after completion of the installation. Abundances, richness and diversity of invertebrates and fish were found to be similar before and after the installation which suggests that the installation had no net negative impact on the site. The Reno mattresses were found to attract fauna typical of rocky shore environments as well as a few invasive alien invertebrate species. This study noted that a hybrid habitat of Reno mattress and eelgrass was created and may in fact provide the positives of both to a system. In any coastal development it will be important to balance the demands of a growing population and the protection of natural habitats. The results of this study suggest that complex artificial structures such as Reno mattresses do provide habitat for fish and invertebrates. However, the use of these structures should be in combination with natural vegetation (e.g. as a hybrid habitat) and not one that replaces intertidal and subtidal natural habitat especially eelgrass. There is limited information regarding the ecological impacts of using Reno mattresses in estuaries and this study provides new information on their ecological efficacy that should be valuable for future coastal erosion control practices.
- Full Text:
- Date Issued: 2020
Initiating biological control for Nymphaea mexicana zuccarini (Nymphaeaceae) in South Africa
- Authors: Reid, Megan Kim
- Date: 2020
- Subjects: Nymphaea mexicana zuccarini -- Biological control -- South Africa , Nymphaeaceae -- Biological control -- South Africa , Invasive plants -- Biological control -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/144510 , vital:38352
- Description: Nymphaea mexicana Zuccarini (Nymphaeaceae) is an aquatic plant originating from south-eastern USA that is becoming increasingly invasive in South Africa as other invasive aquatic plants are being managed successfully through biological control. Mechanical and chemical control of aquatic weeds is expensive, damaging to the environment, and only effective in the short term, so biological control is more desirable as a management strategy for N. mexicana. The biological control of invasive alien plants requires that agents are host specific so that non-target risks are mitigated. For success to be achieved, it is important to ensure that the genetic structure of invasive populations is clarified so that agents can be collected from populations in the native range that match genetically to populations in the invasive range. This is especially important in cases where the morphology of invasive alien plants does not reflect genetic differences between populations. A previous study of the genetic structure of the invasive populations of N. mexicana in South Africa suggests the presence of hybrid forms of the plant in South Africa, with only one of these populations matching with samples from the native range. However, the study only used samples from two sites in the native range using amplified fragment length polymorphisms (AFLPs), so it was necessary to conduct further genetic analyses using samples from more sites in the native range. Hence, the first aim of this study was to develop a better understanding of the genetic structure of N. mexicana populations in the native and invaded range. Genetic samples were collected from sites in the native range during field surveys for potential biological control agents, and inter-simple sequence repeats (ISSRs) were used to compare the genetic structure of invasive and native populations of N. mexicana in South Africa. The results from these analyses suggest that seven of the 14 investigated invasive populations of N. mexicana in South Africa are genetically similar to populations in the native range, while the remaining seven populations are likely to be hybrid forms of the plant. This knowledge will be useful to target populations for biological control and highlights the need for further genetic analyses to determine the parentage of these hybrids so that biological control efforts are more likely to be successful. The initiation of a biological control programme requires that a series of steps are taken in order to maximise the likelihood that this form of intervention will be successful. The first few steps include: identification of the target weed and its genetic structure; exploration in the native range for potential biological control agents; and prioritisation of these agents based on factors such as climatic and genetic compatibility, feeding damage, abundance, and likely host range. Hence, the second aim of this study was to conduct surveys for potential biological control agents in the native range of N. mexicana, and to prioritise these agents. Field surveys were conducted between August and October in 2018 at 17 sites in Florida, Louisiana, and Texas, USA. Sites were selected based on climatic similarity of native sites compared to invasive sites by use of MaxEnt modelling. Native N. mexicana plants were searched for natural enemies, and these were prioritised based on feeding damage, abundance, incidence, and observations of field host range. Two species were prioritised: Bagous americanus LeConte (Coleoptera: Curculionidae) and Megamelus toddi Beamer (Hemiptera: Delphacidae). These species will be imported into quarantine facilities at Rhodes University for host specificity tests to be conducted. Understanding the factors that contribute to the successful establishment of biological control agents is important to improve the efficiency and reduce the costs incurred during the initiation of biological control programmes. Acquiring knowledge of the factors that predict the efficacy of biological control agents is similarly important, and these factors are discussed in the last chapter of this study. The challenges of the biological control of hybrids are also considered, and recommendations are made for the control of N. mexicana and other plants in South Africa.
- Full Text:
- Date Issued: 2020
- Authors: Reid, Megan Kim
- Date: 2020
- Subjects: Nymphaea mexicana zuccarini -- Biological control -- South Africa , Nymphaeaceae -- Biological control -- South Africa , Invasive plants -- Biological control -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/144510 , vital:38352
- Description: Nymphaea mexicana Zuccarini (Nymphaeaceae) is an aquatic plant originating from south-eastern USA that is becoming increasingly invasive in South Africa as other invasive aquatic plants are being managed successfully through biological control. Mechanical and chemical control of aquatic weeds is expensive, damaging to the environment, and only effective in the short term, so biological control is more desirable as a management strategy for N. mexicana. The biological control of invasive alien plants requires that agents are host specific so that non-target risks are mitigated. For success to be achieved, it is important to ensure that the genetic structure of invasive populations is clarified so that agents can be collected from populations in the native range that match genetically to populations in the invasive range. This is especially important in cases where the morphology of invasive alien plants does not reflect genetic differences between populations. A previous study of the genetic structure of the invasive populations of N. mexicana in South Africa suggests the presence of hybrid forms of the plant in South Africa, with only one of these populations matching with samples from the native range. However, the study only used samples from two sites in the native range using amplified fragment length polymorphisms (AFLPs), so it was necessary to conduct further genetic analyses using samples from more sites in the native range. Hence, the first aim of this study was to develop a better understanding of the genetic structure of N. mexicana populations in the native and invaded range. Genetic samples were collected from sites in the native range during field surveys for potential biological control agents, and inter-simple sequence repeats (ISSRs) were used to compare the genetic structure of invasive and native populations of N. mexicana in South Africa. The results from these analyses suggest that seven of the 14 investigated invasive populations of N. mexicana in South Africa are genetically similar to populations in the native range, while the remaining seven populations are likely to be hybrid forms of the plant. This knowledge will be useful to target populations for biological control and highlights the need for further genetic analyses to determine the parentage of these hybrids so that biological control efforts are more likely to be successful. The initiation of a biological control programme requires that a series of steps are taken in order to maximise the likelihood that this form of intervention will be successful. The first few steps include: identification of the target weed and its genetic structure; exploration in the native range for potential biological control agents; and prioritisation of these agents based on factors such as climatic and genetic compatibility, feeding damage, abundance, and likely host range. Hence, the second aim of this study was to conduct surveys for potential biological control agents in the native range of N. mexicana, and to prioritise these agents. Field surveys were conducted between August and October in 2018 at 17 sites in Florida, Louisiana, and Texas, USA. Sites were selected based on climatic similarity of native sites compared to invasive sites by use of MaxEnt modelling. Native N. mexicana plants were searched for natural enemies, and these were prioritised based on feeding damage, abundance, incidence, and observations of field host range. Two species were prioritised: Bagous americanus LeConte (Coleoptera: Curculionidae) and Megamelus toddi Beamer (Hemiptera: Delphacidae). These species will be imported into quarantine facilities at Rhodes University for host specificity tests to be conducted. Understanding the factors that contribute to the successful establishment of biological control agents is important to improve the efficiency and reduce the costs incurred during the initiation of biological control programmes. Acquiring knowledge of the factors that predict the efficacy of biological control agents is similarly important, and these factors are discussed in the last chapter of this study. The challenges of the biological control of hybrids are also considered, and recommendations are made for the control of N. mexicana and other plants in South Africa.
- Full Text:
- Date Issued: 2020
Investigations into biological control options for Lycium ferocissimum Miers, African Boxthorn (Solanaceae) for Australia
- Authors: Mauda, Evans Vusani
- Date: 2020
- Subjects: Lycium ferocissimum , Solanaceae -- Biological control -- Australia , Weeds -- Control -- Australia , Invasive plants -- Biological control -- Australia , Insects as biological pest control agents -- Australia , Insect-plant relationships
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/167142 , vital:41441
- Description: Lycium ferocissimum Miers (Solanaceae) (African boxthorn or boxthorn) is a shrub native to South Africa,and has become naturalised and invasive in Australia and New Zealand. The plant is listed on the Noxious Weed List for Australian States and territories. Although other control methods are available, biological control presents a potentially sustainable intervention for reducing populations of this weed in Australia. In South Africa, the plant has been recorded from two allopatric populations, one in the Eastern Cape Province, the other in the Western Cape Provinces, however, there taxonomic and morphological uncertainties are reported in the literature. Therefore, before native range surveys for potential biological control agents could be considered, the taxonomic uncertainty needed to be resolved. The two geographically distinct areas, as well as the Australia population were sampled to assess morphological and genetic variation. All samples collected in Australia were confirmed as L.ferocissimum, with no evidence of hybridisation with any other Lycium species. Nuclear and chloroplast genetic diversity within L.ferocissimum across South Africa was high, and Australia was low, with no evidence of genetic seperation. One ehaplotypes found across Australia was found at only two sites in South Africa, both in the Western Cape, suggesting that the Australian lineage may have originated from this region. Ten samples from South Africa, putatively identified in the field as L.ferocissimum, were genetically characterised as different (unidentified) Lycium species. The majority of plants sampled were confirmed as L.ferocissimum, sharing a common haplotype (haplotype 5) with sampled specimens from Australia. Morphological analyses across different Lycium species in South Africa did not identify any leaf or floral characteristics unique to L.ferocissimum, and thus morphological identification in the native range remains problematic. Surveys for phytophagous in sects on L.ferocissimum were carried out regularly over a two-year period in the two regions. The number of insect species found in the Eastern Cape Province (55) was higher than in the Western Cape Province (41), but insect diversity based on Shannon indices was highest in the Western Cape Province. Indicator species analysis revealed eight insect herbivore species driving the differences in the herbivore communities between the two provinces. Based on insect distribution, abundance, feeding preference and available literature, three species were prioritised as potential biological control agents. These include the leaf-chewing beetles, Cassida distinguenda Spaeth (Chrysomelidae) and Cleta eckloni Mulsant (Coccinellidae), and the leaf-mining weevil, Neoplatygaster serietuberculata Gyllenhal (Curculionidae). Native range studies such as this are perhaps the most technically difficult and logistically time-consuming part of the biological control programme. Yet, the entire outcome of a programme depends on the suite of potential agents feeding on the weed. The information gained during this stage significantly contributed to the prioritization of agents for further host-range testing and possible release. Here we showed how molecular and genetic characterisations of the target weed can be us ed to accurately define the identity and phylogeny of the target species. In addition, the study also highlighted the importance of considering plant morphology and how phenotypic plasticity may influence infield plant identifications while conducting native range surveys. By gaining further information during long-term and wide spread native range surveys we were not just able to provide a list of herbivorous insect fauna and fungi associated with the plant, but were able to prioritise the phytophagous species that held the most potential as biological control agents.
- Full Text:
- Date Issued: 2020
- Authors: Mauda, Evans Vusani
- Date: 2020
- Subjects: Lycium ferocissimum , Solanaceae -- Biological control -- Australia , Weeds -- Control -- Australia , Invasive plants -- Biological control -- Australia , Insects as biological pest control agents -- Australia , Insect-plant relationships
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/167142 , vital:41441
- Description: Lycium ferocissimum Miers (Solanaceae) (African boxthorn or boxthorn) is a shrub native to South Africa,and has become naturalised and invasive in Australia and New Zealand. The plant is listed on the Noxious Weed List for Australian States and territories. Although other control methods are available, biological control presents a potentially sustainable intervention for reducing populations of this weed in Australia. In South Africa, the plant has been recorded from two allopatric populations, one in the Eastern Cape Province, the other in the Western Cape Provinces, however, there taxonomic and morphological uncertainties are reported in the literature. Therefore, before native range surveys for potential biological control agents could be considered, the taxonomic uncertainty needed to be resolved. The two geographically distinct areas, as well as the Australia population were sampled to assess morphological and genetic variation. All samples collected in Australia were confirmed as L.ferocissimum, with no evidence of hybridisation with any other Lycium species. Nuclear and chloroplast genetic diversity within L.ferocissimum across South Africa was high, and Australia was low, with no evidence of genetic seperation. One ehaplotypes found across Australia was found at only two sites in South Africa, both in the Western Cape, suggesting that the Australian lineage may have originated from this region. Ten samples from South Africa, putatively identified in the field as L.ferocissimum, were genetically characterised as different (unidentified) Lycium species. The majority of plants sampled were confirmed as L.ferocissimum, sharing a common haplotype (haplotype 5) with sampled specimens from Australia. Morphological analyses across different Lycium species in South Africa did not identify any leaf or floral characteristics unique to L.ferocissimum, and thus morphological identification in the native range remains problematic. Surveys for phytophagous in sects on L.ferocissimum were carried out regularly over a two-year period in the two regions. The number of insect species found in the Eastern Cape Province (55) was higher than in the Western Cape Province (41), but insect diversity based on Shannon indices was highest in the Western Cape Province. Indicator species analysis revealed eight insect herbivore species driving the differences in the herbivore communities between the two provinces. Based on insect distribution, abundance, feeding preference and available literature, three species were prioritised as potential biological control agents. These include the leaf-chewing beetles, Cassida distinguenda Spaeth (Chrysomelidae) and Cleta eckloni Mulsant (Coccinellidae), and the leaf-mining weevil, Neoplatygaster serietuberculata Gyllenhal (Curculionidae). Native range studies such as this are perhaps the most technically difficult and logistically time-consuming part of the biological control programme. Yet, the entire outcome of a programme depends on the suite of potential agents feeding on the weed. The information gained during this stage significantly contributed to the prioritization of agents for further host-range testing and possible release. Here we showed how molecular and genetic characterisations of the target weed can be us ed to accurately define the identity and phylogeny of the target species. In addition, the study also highlighted the importance of considering plant morphology and how phenotypic plasticity may influence infield plant identifications while conducting native range surveys. By gaining further information during long-term and wide spread native range surveys we were not just able to provide a list of herbivorous insect fauna and fungi associated with the plant, but were able to prioritise the phytophagous species that held the most potential as biological control agents.
- Full Text:
- Date Issued: 2020
Managing the invasive aquatic plant Sagittaria platyphylla (Engelm.) J.G. Sm(Alismataceae): problems and prospects
- Ndlovu, Mpilonhle Sinothando
- Authors: Ndlovu, Mpilonhle Sinothando
- Date: 2020
- Subjects: Aquatic weeds -- Biological control -- South Africa , Sagittaria latifolia -- Biological control -- South Africa , Noxious weeds -- Biological control -- South Africa , Invasive plants -- Biological control -- South Africa , Listronotus , Insects as biological pest control agents
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167121 , vital:41439
- Description: Sagittaria platyphylla (Engelm.) J.G.Sm. (Alismataceae), commonly known as Delta arrowhead, is an invasive aquatic macrophyte native to southern United States of America (USA) that has become a serious weed in freshwater systems in South Africa, New Zealand, Australia, and recently China. In South Africa, the plant was first detected in Krantzkloof Nature Reserve, KwaZulu-Natal Province in 2008, and due to its known impact in other countries, it was listed as a Category 1a invader species under the National Environmental Management: Biodiversity Act 2004 (NEM: BA). This listing required mechanical and chemical control methods to be implemented by the South African National Biodiversity Institute’s (SANBI), Invasive Species Programme (ISP), with the aim of eradicating the weed. Despite the eradication efforts, by 2016, the weed was recognized as one of the country’s top 10 worst and fastest spreading invasive alien plants. Since its introduction in 2008, the plant has spread both within and between sites in South Africa, increasing from one site in 2008 to 72 sites by 2019. Once introduced into lotic systems, the plant spread rapidly downstream, in some cases up to 120km within six years, with an average of 10 km per year. Extirpation over the last ten years was only possible at a limited number of sites. Under the current management approach, the invasion is foreseen to spread to new sites within a 5 km radius of the current populations. Due to the failure of conventional control mechanisms, biological control is currently being considered as a potential control option. Four potential biological control agents are under investigation, but none have been released. Amongst them is the fruit and flower feeding weevil Listronotus appendiculatus Bohm. (Coleoptera: Curculionidae) which showed most potential as a suitable biological control agent. This study demonstrated that L. appendiculatus herbivory negatively influenced the overall fitness of S. platyphylla by reducing the plant’s growth rate and above ground biomass. Listronotus appendiculatus herbivory also reduced the plant’s size and the potential to kill adult plants. Most importantly, L. appendiculatus larval feeding damage significantly reduce viable-germinating seeds, the weed’s primary dispersal mechanism. Therefore, a biological control programme is advised to be integrated within the current management plan.
- Full Text:
- Date Issued: 2020
- Authors: Ndlovu, Mpilonhle Sinothando
- Date: 2020
- Subjects: Aquatic weeds -- Biological control -- South Africa , Sagittaria latifolia -- Biological control -- South Africa , Noxious weeds -- Biological control -- South Africa , Invasive plants -- Biological control -- South Africa , Listronotus , Insects as biological pest control agents
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167121 , vital:41439
- Description: Sagittaria platyphylla (Engelm.) J.G.Sm. (Alismataceae), commonly known as Delta arrowhead, is an invasive aquatic macrophyte native to southern United States of America (USA) that has become a serious weed in freshwater systems in South Africa, New Zealand, Australia, and recently China. In South Africa, the plant was first detected in Krantzkloof Nature Reserve, KwaZulu-Natal Province in 2008, and due to its known impact in other countries, it was listed as a Category 1a invader species under the National Environmental Management: Biodiversity Act 2004 (NEM: BA). This listing required mechanical and chemical control methods to be implemented by the South African National Biodiversity Institute’s (SANBI), Invasive Species Programme (ISP), with the aim of eradicating the weed. Despite the eradication efforts, by 2016, the weed was recognized as one of the country’s top 10 worst and fastest spreading invasive alien plants. Since its introduction in 2008, the plant has spread both within and between sites in South Africa, increasing from one site in 2008 to 72 sites by 2019. Once introduced into lotic systems, the plant spread rapidly downstream, in some cases up to 120km within six years, with an average of 10 km per year. Extirpation over the last ten years was only possible at a limited number of sites. Under the current management approach, the invasion is foreseen to spread to new sites within a 5 km radius of the current populations. Due to the failure of conventional control mechanisms, biological control is currently being considered as a potential control option. Four potential biological control agents are under investigation, but none have been released. Amongst them is the fruit and flower feeding weevil Listronotus appendiculatus Bohm. (Coleoptera: Curculionidae) which showed most potential as a suitable biological control agent. This study demonstrated that L. appendiculatus herbivory negatively influenced the overall fitness of S. platyphylla by reducing the plant’s growth rate and above ground biomass. Listronotus appendiculatus herbivory also reduced the plant’s size and the potential to kill adult plants. Most importantly, L. appendiculatus larval feeding damage significantly reduce viable-germinating seeds, the weed’s primary dispersal mechanism. Therefore, a biological control programme is advised to be integrated within the current management plan.
- Full Text:
- Date Issued: 2020
Post release evaluation of the distribution and efficacy of Eccritotarsus catarinensis and Eccritotarsus eichhorniae on Pontederia crassipes in South Africa
- Authors: Maseko, Zolile
- Date: 2020
- Subjects: Water hyacinth -- Biological control -- South Africa , Weeds -- Biological control -- South Africa , Miridae -- South Africa , Insects as biological pest control agents -- South Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/143046 , vital:38196
- Description: Biological control involves the release of new species into the environment and therefore, needs to be carefully monitored through post-release assessments which have been largely neglected in the science. Post-release evaluations of biological control programmes reveal whether the control agent has established and if it impacts weed demography, while cost-benefit analyses require a different set of data that show the magnitude on return on investment. The biological control effort on Pontederia crassipes in South Africa uses, amongst others, two species of mirid, Eccritotarsus catarinensis and E. eichhorniae. Initially, they were released as a single species, but were recently divided using molecular techniques. Eccritotarsus catarinensis was released in 1999, and E. eichhorniae in 2007. After many releases over two decades, there was need to assess where each species was established in the country. Molecular techniques proved to be valuable in identifying the two species as they are morphologically indistinguishable in the field. Therefore, molecular techniques should be routinely used for screening biocontrol agents, whether new or as re-introductions. Annual surveys of the mirid release sites around South Africa were undertaken between 2016 and 2019. At each site both insect and plant parameters were measured. Only E. catarinensis is established in the field in South Africa despite the multiple releases of E. eichhorniae at over 70 sites across the country, and E. catarinensis has established at only 22 of the 45 release sites accessed during this study. This thesis tested climate, interaction with other agents already on P. crassipes, and direct competition between the two mirid species as reasons for the lack of establishment of E. eichhorniae. The results of the country-wide surveys showed that climate and water trophic status were the major determinants in the establishment of E. catarinensis. Most of the establishment was recorded in the warmer regions of the country, however, a few populations of the mirid also established in cooler areas, thus demonstrating a degree of thermal plasticity, and possible microclimates as the mirids persisted at sites shaded by riparian vegetation. Stochastic events such as active herbicide campaigns, winter frosts, droughts and floods were responsible for the absence of the mirid at some sites. At some of the eutrophic sites, despite the abundance of E. catarinensis, plants still proliferated as the water trophic status facilitated plant growth, thus, plants were able to compensate for the damage inflicted by the mirid. A more intensive, monthly, post-release evaluation was conducted on the Kubusi River, Eastern Cape Province between 2016 and 2019. This is regarded as one of the cooler water hyacinth sites. Populations of biological control agents at this site fluctuated seasonally. At this site, cold winters caused frosting of the leaves of P. crassipes with the exception of plants growing under overhanging vegetation that provided a refuge for the mirid. But, cool temperatures in the winter months (May to August) severely reduced the populations of E. catarinensis that required a long recovery phase in spring. The consequence of this was that the plants grew unchecked from the onset of the growing season forming dense mats. Of the four agents at the Kubusi River site, Eccritotarsus catarinensis recovered slowest after winter, with lag phases ranging from two months to several months of the three-year period. The release of a suite of agents has implications on the agents themselves, where interactions between the agents can be important. Interactions between pairs and even multiple agents can have implications for biocontrol, where agents are either complimentary or interfere with each other. In this case, because E. catarinensis recovered the slowest of the four agents at the site, plants were of a poor quality by mid-summer resulting in low mirid populations. Competition in weed biological control could be expected to be strongest between pairs of agents that share the same niche, and this could be the reason why E. eichhorniae failed to establish at sites where E. catarinensis had already been established for several years. When the two mirids were combined in manipulated trials in a polytunnel, populations were lower compared to when the two mirids occurred separately. Under warm conditions, it is likely that E. eichhorniae would be the superior agent compared to E. catarinensis. The evaluations discussed in this thesis highlighted gaps in agent release methodology in multispecies settings, as well as the need for strategic augmentation pre- and post-winter. It is important to release agents that will complement each other rather than compete, therefore, when releasing agents in a multispecies setting, niche differentiation needs to be considered. Here it is concluded that the best practice for dealing with the mirids is that they should be released individually, and at sites that have no other biological control agents in order to ultimately assess their efficacy. Landscape level, long-term monitoring of biological control programmes shows the impact of the control programme at a broader scale and, are far more informative than short-term studies and at fewer sites. Long-term post-release evaluations should be mandatory in biological control programmes. Furthermore, these assessments will help develop new strategies or improve on existing ones, thus achieve greater success in control.
- Full Text:
- Date Issued: 2020
- Authors: Maseko, Zolile
- Date: 2020
- Subjects: Water hyacinth -- Biological control -- South Africa , Weeds -- Biological control -- South Africa , Miridae -- South Africa , Insects as biological pest control agents -- South Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/143046 , vital:38196
- Description: Biological control involves the release of new species into the environment and therefore, needs to be carefully monitored through post-release assessments which have been largely neglected in the science. Post-release evaluations of biological control programmes reveal whether the control agent has established and if it impacts weed demography, while cost-benefit analyses require a different set of data that show the magnitude on return on investment. The biological control effort on Pontederia crassipes in South Africa uses, amongst others, two species of mirid, Eccritotarsus catarinensis and E. eichhorniae. Initially, they were released as a single species, but were recently divided using molecular techniques. Eccritotarsus catarinensis was released in 1999, and E. eichhorniae in 2007. After many releases over two decades, there was need to assess where each species was established in the country. Molecular techniques proved to be valuable in identifying the two species as they are morphologically indistinguishable in the field. Therefore, molecular techniques should be routinely used for screening biocontrol agents, whether new or as re-introductions. Annual surveys of the mirid release sites around South Africa were undertaken between 2016 and 2019. At each site both insect and plant parameters were measured. Only E. catarinensis is established in the field in South Africa despite the multiple releases of E. eichhorniae at over 70 sites across the country, and E. catarinensis has established at only 22 of the 45 release sites accessed during this study. This thesis tested climate, interaction with other agents already on P. crassipes, and direct competition between the two mirid species as reasons for the lack of establishment of E. eichhorniae. The results of the country-wide surveys showed that climate and water trophic status were the major determinants in the establishment of E. catarinensis. Most of the establishment was recorded in the warmer regions of the country, however, a few populations of the mirid also established in cooler areas, thus demonstrating a degree of thermal plasticity, and possible microclimates as the mirids persisted at sites shaded by riparian vegetation. Stochastic events such as active herbicide campaigns, winter frosts, droughts and floods were responsible for the absence of the mirid at some sites. At some of the eutrophic sites, despite the abundance of E. catarinensis, plants still proliferated as the water trophic status facilitated plant growth, thus, plants were able to compensate for the damage inflicted by the mirid. A more intensive, monthly, post-release evaluation was conducted on the Kubusi River, Eastern Cape Province between 2016 and 2019. This is regarded as one of the cooler water hyacinth sites. Populations of biological control agents at this site fluctuated seasonally. At this site, cold winters caused frosting of the leaves of P. crassipes with the exception of plants growing under overhanging vegetation that provided a refuge for the mirid. But, cool temperatures in the winter months (May to August) severely reduced the populations of E. catarinensis that required a long recovery phase in spring. The consequence of this was that the plants grew unchecked from the onset of the growing season forming dense mats. Of the four agents at the Kubusi River site, Eccritotarsus catarinensis recovered slowest after winter, with lag phases ranging from two months to several months of the three-year period. The release of a suite of agents has implications on the agents themselves, where interactions between the agents can be important. Interactions between pairs and even multiple agents can have implications for biocontrol, where agents are either complimentary or interfere with each other. In this case, because E. catarinensis recovered the slowest of the four agents at the site, plants were of a poor quality by mid-summer resulting in low mirid populations. Competition in weed biological control could be expected to be strongest between pairs of agents that share the same niche, and this could be the reason why E. eichhorniae failed to establish at sites where E. catarinensis had already been established for several years. When the two mirids were combined in manipulated trials in a polytunnel, populations were lower compared to when the two mirids occurred separately. Under warm conditions, it is likely that E. eichhorniae would be the superior agent compared to E. catarinensis. The evaluations discussed in this thesis highlighted gaps in agent release methodology in multispecies settings, as well as the need for strategic augmentation pre- and post-winter. It is important to release agents that will complement each other rather than compete, therefore, when releasing agents in a multispecies setting, niche differentiation needs to be considered. Here it is concluded that the best practice for dealing with the mirids is that they should be released individually, and at sites that have no other biological control agents in order to ultimately assess their efficacy. Landscape level, long-term monitoring of biological control programmes shows the impact of the control programme at a broader scale and, are far more informative than short-term studies and at fewer sites. Long-term post-release evaluations should be mandatory in biological control programmes. Furthermore, these assessments will help develop new strategies or improve on existing ones, thus achieve greater success in control.
- Full Text:
- Date Issued: 2020
Quantifying ecosystem restoration recovery and restoration practice following the biological control of invasive alien macrophytes in Southern Africa
- Authors: Motitsoe, Samuel Nkopane
- Date: 2020
- Subjects: Salvinia molesta , Ceratophyllum demersum , Nymphaea mexicana , Invasive plants -- Biological control -- South Africa , Aquatic weeds -- Biological control -- South Africa , Restoration monitoring (Ecology) -- South Africa , Biolotical invasions -- Environmental aspects
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/167519 , vital:41488
- Description: Invasive alien aquatic plants (IAAP) species are known to have deleterious effects on the freshwater ecosystems they invade. This includes both socio-economic and ecologically important ecosystem goods and services. Thus, IAAP species are declared a serious threat, second only to habitat modification for causing a loss of aquatic biodiversity. Three control methods have been widely applied to control IAAP species invasion globally; mechanical, chemical and biological control. Both mechanical and chemical control methods are considered short-term and expensive, whereas biological control methods are regarded an effective and long-term solution for IAAP species control at the landscape level. But, little is known of the ecological recovery following the biological control of IAAP species, with mechanical control known to have had mixed success and chemical control to have non-targeted effects on aquatic ecosystems, causing harm to wildlife and human well-being. Biological control practitioners measure the success of biological control based on: (1) the biological control agents’ establishment and the negative impacts they impose on the targeted weed; and (2) the weeds biomass reduction and an increase in native macrophytes species. Arguably, measures of biological control success have been subjective and variable across the globe. Although some field studies have demonstrated biological control success to have positive socio-economic returns, there is little literature on ecological benefits. Furthermore, there is limited understanding on ecosystem recovery and possible restoration efforts following the biological control IAAP species, as compared to alien weeds in terrestrial and riparian ecosystems. Thus, this thesis aimed to quantify the ecological recovery i.e. aquatic biodiversity, ecosystem processes and trophic interactions following the management of Salvinia molesta in freshwater ecosystems. The research employed a suite of Before-After Control-Impact mesocosm and field studies to investigate the response of aquatic microalgae, macroinvertebrates and their interactions (food web structure and function) during S. molesta infestation and after mechanical and biological control. The mesocosm experiment (Before invasion, During invasion & After control) showed that both aquatic microalgae and macroinvertebrate diversity indices were reliable biological indicators of S. molesta ecological impacts and recovery following control. The restored treatment (100% S. molesta cover + biological control agents), demonstrated complete aquatic microalgae and macroinvertebrate recovery following biological control, similar to the control treatment (open water), where the degraded/impacted treatment (100% S. molesta cover with no biological control agents) showed a drastic decline in aquatic biodiversity and a complete shift in aquatic biota assemblage structure. Thus, the biological control effort by Cyrtobagous salviniae, the biological control agent for S. molesta, assisted in the recovery of aquatic biota following successful biological control. The field study (four field sites, two sites controlled mechanically and two biologically) investigated water quality, aquatic biodiversity and community trophic interactions (aquatic food web) “before and after” S. molesta control. The study showed a drastic decline in aquatic biodiversity (with three sites showing no record of aquatic macroinvertebrates, thus no biotic interactions during infestation) and poor water quality due to the shade-effect (light barrier due to floating S. molesta mats on the water surface) during the “before” S. molesta control phase. However, following both mechanical and biological control (“after” S. molesta control phase), there was a significant shift in abiotic and biotic ecosystem characteristics as compared to the “before” S. molesta control phase. Thus, rapid ecosystem recovery was apparent as a result of aquatic microalgae and macroinvertebrates recolonisation. Sites showed a normal functioning ecosystem where improved water quality, increased biodiversity, productivity and trophic interactions, was indicative of the return of biologically and functionally important species which were lost during the “before” S. molesta phase. Although the clear water state showed positive outcomes at Westlake River, these were short lived when the system was dominated by a cosmopolitan submerged Ceratophyllum demersum, and later replaced by a floating-leaved emergent IAAP Nymphaea mexicana. Each state was responsible for a significant shift in both biotic and abiotic characteristics, affirming macrophyte abilities to influence aquatic environments structure and functions. Furthermore, this event showed a clear example of a secondary invasion. Thus, a holistic IAAP species management strategy is necessary to restore previously invaded ecosystems and prevent subsequent secondary invasion and ecosystem degradation. In conclusion, the S. molesta shade-effect like any other free-floating IAAP species, was identified as the main degrading factor and responsible for water quality reduction, loss of aquatic diversity and shift in aquatic biota assemblage structure. Following S. molesta removal (or shade-effect elimination), there was a positive response to aquatic ecosystem species abundance, richness, diversity and community structure. Therefore, in combination, aquatic biota recolonisation rate and increases in biological and functional diversity were instrumental in the recovery of ecosystem structure and functions, following the control of S. molesta. Echoing existing literature, this thesis recommends: (1) IAAP species management programmes (mechanical and/or biological control) should not only aim to control the weed but also focus on ecosystems recovery and possible restoration goals; (2) biological control should be used where appropriate to combat free-floating IAAP species in freshwater ecosystems, followed by active introduction of native macrophyte propagules since they are limited by anthropogenic activities; and (3) more freshwater case studies are needed to add to our understanding of IAAP species management and restoration effort incorporating long-term monitoring.
- Full Text:
- Date Issued: 2020
- Authors: Motitsoe, Samuel Nkopane
- Date: 2020
- Subjects: Salvinia molesta , Ceratophyllum demersum , Nymphaea mexicana , Invasive plants -- Biological control -- South Africa , Aquatic weeds -- Biological control -- South Africa , Restoration monitoring (Ecology) -- South Africa , Biolotical invasions -- Environmental aspects
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/167519 , vital:41488
- Description: Invasive alien aquatic plants (IAAP) species are known to have deleterious effects on the freshwater ecosystems they invade. This includes both socio-economic and ecologically important ecosystem goods and services. Thus, IAAP species are declared a serious threat, second only to habitat modification for causing a loss of aquatic biodiversity. Three control methods have been widely applied to control IAAP species invasion globally; mechanical, chemical and biological control. Both mechanical and chemical control methods are considered short-term and expensive, whereas biological control methods are regarded an effective and long-term solution for IAAP species control at the landscape level. But, little is known of the ecological recovery following the biological control of IAAP species, with mechanical control known to have had mixed success and chemical control to have non-targeted effects on aquatic ecosystems, causing harm to wildlife and human well-being. Biological control practitioners measure the success of biological control based on: (1) the biological control agents’ establishment and the negative impacts they impose on the targeted weed; and (2) the weeds biomass reduction and an increase in native macrophytes species. Arguably, measures of biological control success have been subjective and variable across the globe. Although some field studies have demonstrated biological control success to have positive socio-economic returns, there is little literature on ecological benefits. Furthermore, there is limited understanding on ecosystem recovery and possible restoration efforts following the biological control IAAP species, as compared to alien weeds in terrestrial and riparian ecosystems. Thus, this thesis aimed to quantify the ecological recovery i.e. aquatic biodiversity, ecosystem processes and trophic interactions following the management of Salvinia molesta in freshwater ecosystems. The research employed a suite of Before-After Control-Impact mesocosm and field studies to investigate the response of aquatic microalgae, macroinvertebrates and their interactions (food web structure and function) during S. molesta infestation and after mechanical and biological control. The mesocosm experiment (Before invasion, During invasion & After control) showed that both aquatic microalgae and macroinvertebrate diversity indices were reliable biological indicators of S. molesta ecological impacts and recovery following control. The restored treatment (100% S. molesta cover + biological control agents), demonstrated complete aquatic microalgae and macroinvertebrate recovery following biological control, similar to the control treatment (open water), where the degraded/impacted treatment (100% S. molesta cover with no biological control agents) showed a drastic decline in aquatic biodiversity and a complete shift in aquatic biota assemblage structure. Thus, the biological control effort by Cyrtobagous salviniae, the biological control agent for S. molesta, assisted in the recovery of aquatic biota following successful biological control. The field study (four field sites, two sites controlled mechanically and two biologically) investigated water quality, aquatic biodiversity and community trophic interactions (aquatic food web) “before and after” S. molesta control. The study showed a drastic decline in aquatic biodiversity (with three sites showing no record of aquatic macroinvertebrates, thus no biotic interactions during infestation) and poor water quality due to the shade-effect (light barrier due to floating S. molesta mats on the water surface) during the “before” S. molesta control phase. However, following both mechanical and biological control (“after” S. molesta control phase), there was a significant shift in abiotic and biotic ecosystem characteristics as compared to the “before” S. molesta control phase. Thus, rapid ecosystem recovery was apparent as a result of aquatic microalgae and macroinvertebrates recolonisation. Sites showed a normal functioning ecosystem where improved water quality, increased biodiversity, productivity and trophic interactions, was indicative of the return of biologically and functionally important species which were lost during the “before” S. molesta phase. Although the clear water state showed positive outcomes at Westlake River, these were short lived when the system was dominated by a cosmopolitan submerged Ceratophyllum demersum, and later replaced by a floating-leaved emergent IAAP Nymphaea mexicana. Each state was responsible for a significant shift in both biotic and abiotic characteristics, affirming macrophyte abilities to influence aquatic environments structure and functions. Furthermore, this event showed a clear example of a secondary invasion. Thus, a holistic IAAP species management strategy is necessary to restore previously invaded ecosystems and prevent subsequent secondary invasion and ecosystem degradation. In conclusion, the S. molesta shade-effect like any other free-floating IAAP species, was identified as the main degrading factor and responsible for water quality reduction, loss of aquatic diversity and shift in aquatic biota assemblage structure. Following S. molesta removal (or shade-effect elimination), there was a positive response to aquatic ecosystem species abundance, richness, diversity and community structure. Therefore, in combination, aquatic biota recolonisation rate and increases in biological and functional diversity were instrumental in the recovery of ecosystem structure and functions, following the control of S. molesta. Echoing existing literature, this thesis recommends: (1) IAAP species management programmes (mechanical and/or biological control) should not only aim to control the weed but also focus on ecosystems recovery and possible restoration goals; (2) biological control should be used where appropriate to combat free-floating IAAP species in freshwater ecosystems, followed by active introduction of native macrophyte propagules since they are limited by anthropogenic activities; and (3) more freshwater case studies are needed to add to our understanding of IAAP species management and restoration effort incorporating long-term monitoring.
- Full Text:
- Date Issued: 2020