Assessing the invasive status and reproductive ecology of two Crataegus species in South Africa; Crataegus monogyna Jacq and C. mexicana DC
- Authors: Tshilingalinga, Sydney
- Date: 2021-03
- Subjects: Crataegus monogyna , Nonindigenous pests , Biological invasions
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/20904 , vital:46740
- Description: In South Africa different species, from the genus Crataegus, including Crataegus monogyna Jacq and C. mexicana DC have been introduced for various reasons in the past. Populations of these plants have now established in multiple provinces. However, the invasive status, risk and insect pollinators that promote their reproduction and dispersal have never been studied in South Africa. This study was aimed at 1) Assessing the risk of, and mapping two Crataegus species, Crataegus monogyna Jacq and C. mexicana DC in South Africa, 2) Determining the role and effectiveness of insects pollinators to fruiting of C. monogyna and C. mexicana, 3) Identifying flower visitors of C. monogyna and C. mexicana, and 4) documenting potential dispersal vectors for both species in the Eastern Cape Province. A framework entitled “Framework and guideline for conducting risk analysis under NEM: BA Alien and Invasive Species Regulation of 2014” was used to assess the risk of the two Crataegus spp, and we conducted field trips to various provinces in SA to map their distribution. The author conducted an exclusion experiment to determine the role and effectiveness of insect pollinators. Observations were conducted to identify flower visitors and potential dispersal vectors for both species. The risk analysis results suggested that both species pose a high risk of becoming invasive in South Africa. The eradication feasibility of both species was found to be medium with C. monogyna having an eradication feasibility score of 5 and C. mexicana having an eradication feasibility score of 4. This meant that there was a 50 percent chance for both species to be eradicated in South Africa currently. After a thorough risk analysis, it was recommended that both species be listed under category 1b on the National Environmental Management Biodiversity Act. Category 1b species are invasive species that need to be controlled, and if possible, they must be eradicated, trading of species from this category is not allowed. Crataegus mexicana was found to be widespread in South Africa with ten relatively small populations distributed in 5 provinces; Limpopo, Mpumalanga, KwaZulu-Natal, Free State and Eastern Cape Province. Crataegus monogyna was found not to be widespread in South Africa, with only three populations found in the Eastern Cape Province. Insect pollinators contribute to the fruiting of both species in SA. However, the exotic plants were also observed to be able to self-pollinate when insects are excluded. Flowers of C. monogyna were visited by various insect species from orders Lepidoptera, Hymenoptera, Coleoptera and Diptera, while C. mexicana is visited by species from the order Hymenoptera, Diptera, Lepidoptera and Coleoptera. Seventy-seven percent (77 percent) of potential dispersal vectors observed for C. monogyna were birds, and 15 percent were mammals. For C. mexicana, 71 percent of potential dispersal vectors observed were mammals, and 29 percent were birds. Crataegus monogyna and C. mexicana are emerging invasive alien species in South Africa, and not much is known about them. Although the two species are listed as invasive weeds in South Africa, very little is known about their invasive status in other parts of the world. This study has managed to give baseline information and data about both species which are already in South Africa. The baseline information and data include the population structure of both species, their distribution, the risk they pose to South Africa biodiversity and their reproduction ecology. Currently, there are no management plans in place for both species in South Africa, and this is because they are not listed yet in the National Environmental Management Biodiversity Act of South Africa. However, this study recommends that current populations continue to be monitored, awareness of both species in various provinces be initiated to help in the discovery of new and emerging populations, and management options of large populations developed in the future. , Thesis (MSc) (Entomology) -- University of Fort Hare, 2021
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- Date Issued: 2021-03
The effects of the invasive mussel mytilus galloprovincialis and human exploitation on the indigenous mussel Perna perna on the South Coast of South Africa
- Authors: Rius Viladomiu, Marc
- Date: 2005
- Subjects: Mussels -- South Africa , Perna -- South Africa , Mytilus galloprovincialis -- South Africa , Mytilidae -- South Africa , Biological invasions , Marine resources conservation -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5684 , http://hdl.handle.net/10962/d1005370 , Mussels -- South Africa , Perna -- South Africa , Mytilus galloprovincialis -- South Africa , Mytilidae -- South Africa , Biological invasions , Marine resources conservation -- South Africa
- Description: In South Africa, the indigenous mussel Perna perna is threatened by both an invasive species and excessive human exploitation. The Mediterranean mussel Mytilus galloprovincialis is an invasive species that has been introduced to many parts of the world. In South Africa, this species arrived in the 1970s and spread rapidly along the west coast where today it is the dominant mussel species. Along the west coast, M. galloprovincialis is competitively superior in all aspects to the indigenous mussel species, and, as a result, has displaced some of them. On the south coast, M. galloprovincialis found more oligotrophic waters, higher species richness, and a stronger competitor in the indigenous mussel P. perna. The rate of spread of M. galloprovincialis along the south coast has decreased over the last 10 years and the present eastern limit of its distribution in South African is East London. On the south coast, M. galloprovincialis has not yet completely replaced P. perna; instead, the two exhibit spatial segregation, with P. perna dominating the low shore, M. galloprovincialis the high shore and an overlap zone between the two. An experiment on competition was carried out at one site on the south coast. The results showed that, on the low shore, P. perna is a more dominant competitor for space than M. galloprovincialis. Also byssus attachment of the two species differs, P. perna being much stronger than M. galloprovincialis, which suffers high mortality due to wave action on the low shore, especially in monospecific beds. As a result, mortality of M. galloprovincialis through wave action is reduced by the presence of P. perna, which seems to confer protection against dislodgement. However, in the absence of strong wave action, P. perna competitively excludes M. galloprovincialis. Human exploitation along 160 km of coast was examined by sampling mussel populations and using aerial surveys to determine where harvesters were distributed. Collectors did not seem to discriminate between species. The study has shown that higher abundances of mussels were found in protected or inaccessible sites, while in unprotected sites mussels were scarce. Coastal nature reserves are being proven to be effective in protecting mussel populations.
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- Date Issued: 2005