Prey and predator density‐dependent interactions under different water volumes
- Cuthbert, Ross N, Dalu, Tatenda, Wasserman, Ryan J, Sentis, Arnaud, Weyl, Olaf L F, Froneman, P William, Callaghan, Amanda, Dick, Jaimie T A
- Authors: Cuthbert, Ross N , Dalu, Tatenda , Wasserman, Ryan J , Sentis, Arnaud , Weyl, Olaf L F , Froneman, P William , Callaghan, Amanda , Dick, Jaimie T A
- Date: 2021
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/466957 , vital:76802 , https://doi.org/10.1002/ece3.7503
- Description: Predation is a critical ecological process that directly and indirectly mediates population stabilities, as well as ecosystem structure and function. The strength of interactions between predators and prey may be mediated by multiple density dependences concerning numbers of predators and prey. In temporary wetland ecosystems in particular, fluctuating water volumes may alter predation rates through differing search space and prey encounter rates. Using a functional response approach, we examined the influence of predator and prey densities on interaction strengths of the temporary pond specialist copepod Lovenula raynerae preying on cladoceran prey, Daphnia pulex, under contrasting water volumes. Further, using a population dynamic modeling approach, we quantified multiple predator effects across differences in prey density and water volume. Predators exhibited type II functional responses under both water volumes, with significant antagonistic multiple predator effects (i.e., antagonisms) exhibited overall. The strengths of antagonistic interactions were, however, enhanced under reduced water volumes and at intermediate prey densities. These findings indicate important biotic and abiotic contexts that mediate predator–prey dynamics, whereby multiple predator effects are contingent on both prey density and search area characteristics. In particular, reduced search areas (i.e., water volumes) under intermediate prey densities could enhance antagonisms by heightening predator–predator interference effects.
- Full Text:
- Date Issued: 2021
- Authors: Cuthbert, Ross N , Dalu, Tatenda , Wasserman, Ryan J , Sentis, Arnaud , Weyl, Olaf L F , Froneman, P William , Callaghan, Amanda , Dick, Jaimie T A
- Date: 2021
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/466957 , vital:76802 , https://doi.org/10.1002/ece3.7503
- Description: Predation is a critical ecological process that directly and indirectly mediates population stabilities, as well as ecosystem structure and function. The strength of interactions between predators and prey may be mediated by multiple density dependences concerning numbers of predators and prey. In temporary wetland ecosystems in particular, fluctuating water volumes may alter predation rates through differing search space and prey encounter rates. Using a functional response approach, we examined the influence of predator and prey densities on interaction strengths of the temporary pond specialist copepod Lovenula raynerae preying on cladoceran prey, Daphnia pulex, under contrasting water volumes. Further, using a population dynamic modeling approach, we quantified multiple predator effects across differences in prey density and water volume. Predators exhibited type II functional responses under both water volumes, with significant antagonistic multiple predator effects (i.e., antagonisms) exhibited overall. The strengths of antagonistic interactions were, however, enhanced under reduced water volumes and at intermediate prey densities. These findings indicate important biotic and abiotic contexts that mediate predator–prey dynamics, whereby multiple predator effects are contingent on both prey density and search area characteristics. In particular, reduced search areas (i.e., water volumes) under intermediate prey densities could enhance antagonisms by heightening predator–predator interference effects.
- Full Text:
- Date Issued: 2021
Alternative prey impedes the efficacy of a natural enemy of mosquitoes
- Cuthbert, Ross N, Dalu, Tatenda, Wasserman, Ryan J, Weyl, Olaf L F, Froneman, P William, Callaghan, Amanda, Coughlan, Neil E, Dick, Jaimie T A
- Authors: Cuthbert, Ross N , Dalu, Tatenda , Wasserman, Ryan J , Weyl, Olaf L F , Froneman, P William , Callaghan, Amanda , Coughlan, Neil E , Dick, Jaimie T A
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/467148 , vital:76831 , https://doi.org/10.1016/j.biocontrol.2019.104146
- Description: Adaptive foraging behaviour in the presence of multiple prey types may mediate stability to predator-prey relationships. For biological control agents, the presence of alternative prey may thus reduce ecological impacts towards target organisms, presenting a key challenge to the derivation of agent efficacies. Quantifications of non-target effects are especially important for generalist biocontrol agents in their regulation of pests, vectors and invasive species. We examined the predatory impact of the notonectid Anisops debilis towards larvae of the vector mosquito complex Culex pipiens in the presence of varying densities of alternative daphniid prey. Experimentally, we quantified functional responses of A. debilis towards target mosquito prey under different background daphniid compositions, and also tested for prey switching propensities by the notonectid predator.
- Full Text:
- Date Issued: 2020
- Authors: Cuthbert, Ross N , Dalu, Tatenda , Wasserman, Ryan J , Weyl, Olaf L F , Froneman, P William , Callaghan, Amanda , Coughlan, Neil E , Dick, Jaimie T A
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/467148 , vital:76831 , https://doi.org/10.1016/j.biocontrol.2019.104146
- Description: Adaptive foraging behaviour in the presence of multiple prey types may mediate stability to predator-prey relationships. For biological control agents, the presence of alternative prey may thus reduce ecological impacts towards target organisms, presenting a key challenge to the derivation of agent efficacies. Quantifications of non-target effects are especially important for generalist biocontrol agents in their regulation of pests, vectors and invasive species. We examined the predatory impact of the notonectid Anisops debilis towards larvae of the vector mosquito complex Culex pipiens in the presence of varying densities of alternative daphniid prey. Experimentally, we quantified functional responses of A. debilis towards target mosquito prey under different background daphniid compositions, and also tested for prey switching propensities by the notonectid predator.
- Full Text:
- Date Issued: 2020
Assessing sediment particle-size effects on benthic algal colonisation and total carbohydrate production
- Dalu, Tatenda, Cuthbert, Ross N, Chavalala, Tiyisani L, Froneman, P William, Wasserman, Ryan J
- Authors: Dalu, Tatenda , Cuthbert, Ross N , Chavalala, Tiyisani L , Froneman, P William , Wasserman, Ryan J
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/466815 , vital:76789 , https://doi.org/10.1016/j.scitotenv.2019.136348
- Description: Increased sedimentation and siltation associated with anthropogenic environmental change may alter microbial biofilms and the carbohydrates they produce, with potential bottom-up effects in these ecosystems. The present study aimed to examine to what extent carbohydrate (associated with biofilm exopolymer) concentration and benthic algal biomass vary among different sediment types (size-structure categories) using a microcosm experiment conducted over a period of 28 days. Substrate treatment and time had a significant effect on the total chlorophyll-a concentrations, whilst a significant interaction was present in the case of total sediment carbohydrates. Total sediment carbohydrates did not relate significantly to chlorophyll-a concentrations overall, nor for any substrate treatments owing to a non-significant ‘chlorophyll-a × substrate’ interaction term. The diatom community characteristics across sediment sizes were unique for each treatment in our study, with unique dominant diatom taxa compositions within each sediment size class. The finest sediment particle-size (greater than 63 μm) may be the least stable, most likely due to lower binding. We anticipate that the current study findings will lead to a better understanding of how different sediment types due to sedimentation and siltation will impact on primary productivity and the composition of diatom communities in aquatic systems.
- Full Text:
- Date Issued: 2020
- Authors: Dalu, Tatenda , Cuthbert, Ross N , Chavalala, Tiyisani L , Froneman, P William , Wasserman, Ryan J
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/466815 , vital:76789 , https://doi.org/10.1016/j.scitotenv.2019.136348
- Description: Increased sedimentation and siltation associated with anthropogenic environmental change may alter microbial biofilms and the carbohydrates they produce, with potential bottom-up effects in these ecosystems. The present study aimed to examine to what extent carbohydrate (associated with biofilm exopolymer) concentration and benthic algal biomass vary among different sediment types (size-structure categories) using a microcosm experiment conducted over a period of 28 days. Substrate treatment and time had a significant effect on the total chlorophyll-a concentrations, whilst a significant interaction was present in the case of total sediment carbohydrates. Total sediment carbohydrates did not relate significantly to chlorophyll-a concentrations overall, nor for any substrate treatments owing to a non-significant ‘chlorophyll-a × substrate’ interaction term. The diatom community characteristics across sediment sizes were unique for each treatment in our study, with unique dominant diatom taxa compositions within each sediment size class. The finest sediment particle-size (greater than 63 μm) may be the least stable, most likely due to lower binding. We anticipate that the current study findings will lead to a better understanding of how different sediment types due to sedimentation and siltation will impact on primary productivity and the composition of diatom communities in aquatic systems.
- Full Text:
- Date Issued: 2020
Benthic diatom-based indices and isotopic biomonitoring of nitrogen pollution in a warm temperate Austral river system
- Dalu, Tatenda, Cuthbert, Ross N, Taylor, Jonathan C, Magoro, Mandla L, Weyl, Olaf L F, Froneman, P William, Wasserman, Ryan J
- Authors: Dalu, Tatenda , Cuthbert, Ross N , Taylor, Jonathan C , Magoro, Mandla L , Weyl, Olaf L F , Froneman, P William , Wasserman, Ryan J
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/466917 , vital:76798 , https://doi.org/10.1016/j.scitotenv.2020.142452
- Description: Rivers are impacted by pollutants from anthropogenic activities such as urbanisation and agricultural practices. Whilst point source pollution has been widely studied and in some cases remediated, non-point pollutant sources remain pervasive, particularly in developing countries that lack economic and human specialist capacity. Monitoring of pollution levels in many regions is additionally challenged by a lack of robust indicators for nitrogen inputs, however, diatom community indices and analysis of variation in microphytobenthos (MBP) stable isotope analysis variations have potential. The present study investigates variations and utilities in benthic diatom indices and MPB δ15N along different river sections (n = 31) of an austral river between two seasons (wet and dry), testing for relationships with key environmental variables (physical, water and sediment), in the context of N monitoring. One hundred and eighteen diatom taxa belonging to 36 genera were identified, with physical (water flow), water (nitrate, P and total dissolved solids) and sediment (B, Ca, Cr, Na, N, P, SOM, Pb and Zn) variables correlating to one or more of the 12 diatom indices presented. In particular, Biological Diatom Index, Biological Index of Water Quality, Central Economic Community, Index of Artois-Picardie Diatom (IDAP) and Sládeček's Index were strongly explained by sediment variables, whilst Descy's Pollution Index and Schiefele and Schreiner's Index were explained by water and physical variables.
- Full Text:
- Date Issued: 2020
- Authors: Dalu, Tatenda , Cuthbert, Ross N , Taylor, Jonathan C , Magoro, Mandla L , Weyl, Olaf L F , Froneman, P William , Wasserman, Ryan J
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/466917 , vital:76798 , https://doi.org/10.1016/j.scitotenv.2020.142452
- Description: Rivers are impacted by pollutants from anthropogenic activities such as urbanisation and agricultural practices. Whilst point source pollution has been widely studied and in some cases remediated, non-point pollutant sources remain pervasive, particularly in developing countries that lack economic and human specialist capacity. Monitoring of pollution levels in many regions is additionally challenged by a lack of robust indicators for nitrogen inputs, however, diatom community indices and analysis of variation in microphytobenthos (MBP) stable isotope analysis variations have potential. The present study investigates variations and utilities in benthic diatom indices and MPB δ15N along different river sections (n = 31) of an austral river between two seasons (wet and dry), testing for relationships with key environmental variables (physical, water and sediment), in the context of N monitoring. One hundred and eighteen diatom taxa belonging to 36 genera were identified, with physical (water flow), water (nitrate, P and total dissolved solids) and sediment (B, Ca, Cr, Na, N, P, SOM, Pb and Zn) variables correlating to one or more of the 12 diatom indices presented. In particular, Biological Diatom Index, Biological Index of Water Quality, Central Economic Community, Index of Artois-Picardie Diatom (IDAP) and Sládeček's Index were strongly explained by sediment variables, whilst Descy's Pollution Index and Schiefele and Schreiner's Index were explained by water and physical variables.
- Full Text:
- Date Issued: 2020
Examining intraspecific multiple predator effects across shifting predator sex ratios:
- Cuthbert, Ross N, Dalu, Tatenda, Wasserman, Ryan J, Weyl, Olaf L F, Froneman, P William, Callaghan, Amanda, Dick, Jaimie T A
- Authors: Cuthbert, Ross N , Dalu, Tatenda , Wasserman, Ryan J , Weyl, Olaf L F , Froneman, P William , Callaghan, Amanda , Dick, Jaimie T A
- Date: 2020
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/150119 , vital:38941 , https://doi.org/10.1016/j.baae.2020.03.002
- Description: Predator-predator interactions, or “multiple predator effects” (MPEs), are pervasive in the structuring of communities and complicate predictive quantifications of ecosystem dynamics. The nature of MPEs is also context-dependent, manifesting differently among species, prey densities and habitat structures. However, there has hitherto been a lack of consideration for the implications of intraspecific demographic variation within populations for the strength of MPEs. The present study extends MPE concepts to examine intraspecific interactions among male and female predators across differences in prey densities using a functional response approach. Focusing on a copepod-mosquito model predator-prey system, interaction strengths of different sex ratio pairs of Lovenula raynerae were quantified towards larval Culex pipiens complex prey, with observations compared to both additive and substitutive model predictions.
- Full Text:
- Date Issued: 2020
- Authors: Cuthbert, Ross N , Dalu, Tatenda , Wasserman, Ryan J , Weyl, Olaf L F , Froneman, P William , Callaghan, Amanda , Dick, Jaimie T A
- Date: 2020
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/150119 , vital:38941 , https://doi.org/10.1016/j.baae.2020.03.002
- Description: Predator-predator interactions, or “multiple predator effects” (MPEs), are pervasive in the structuring of communities and complicate predictive quantifications of ecosystem dynamics. The nature of MPEs is also context-dependent, manifesting differently among species, prey densities and habitat structures. However, there has hitherto been a lack of consideration for the implications of intraspecific demographic variation within populations for the strength of MPEs. The present study extends MPE concepts to examine intraspecific interactions among male and female predators across differences in prey densities using a functional response approach. Focusing on a copepod-mosquito model predator-prey system, interaction strengths of different sex ratio pairs of Lovenula raynerae were quantified towards larval Culex pipiens complex prey, with observations compared to both additive and substitutive model predictions.
- Full Text:
- Date Issued: 2020
Inter-population similarities and differences in predation efficiency of a mosquito natural enemy
- Cuthbert, Ross N, Dalu, Tatenda, Wasserman, Ryan J, Weyl, Olaf L F, Froneman, P William, Callaghan, Amanda, Dick, Jaimie T A
- Authors: Cuthbert, Ross N , Dalu, Tatenda , Wasserman, Ryan J , Weyl, Olaf L F , Froneman, P William , Callaghan, Amanda , Dick, Jaimie T A
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/466928 , vital:76799 , https://doi.org/10.1093/jme/tjaa093
- Description: Predation is a critical factor that mediates population stability, community structure, and ecosystem function. Predatory natural enemies can contribute to the regulation of disease vector groups such as mosquitoes, particularly where they naturally co-occur across landscapes. However, we must understand inter-population variation in predatory efficiency if we are to enhance vector control. The present study thus employs a functional response (FR; resource use under different densities) approach to quantify and compare predatory interaction strengths among six populations of a predatory temporary pond specialist copepod, Lovenula raynerae, from the Eastern Cape of South Africa preying on second instar Culex pipiens complex mosquito larvae.
- Full Text:
- Date Issued: 2020
- Authors: Cuthbert, Ross N , Dalu, Tatenda , Wasserman, Ryan J , Weyl, Olaf L F , Froneman, P William , Callaghan, Amanda , Dick, Jaimie T A
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/466928 , vital:76799 , https://doi.org/10.1093/jme/tjaa093
- Description: Predation is a critical factor that mediates population stability, community structure, and ecosystem function. Predatory natural enemies can contribute to the regulation of disease vector groups such as mosquitoes, particularly where they naturally co-occur across landscapes. However, we must understand inter-population variation in predatory efficiency if we are to enhance vector control. The present study thus employs a functional response (FR; resource use under different densities) approach to quantify and compare predatory interaction strengths among six populations of a predatory temporary pond specialist copepod, Lovenula raynerae, from the Eastern Cape of South Africa preying on second instar Culex pipiens complex mosquito larvae.
- Full Text:
- Date Issued: 2020
Lack of prey switching and strong preference for mosquito prey by a temporary pond specialist predator
- Cuthbert, Ross N, Dalu, Tatenda, Wasserman, Ryan J, Weyl, Olaf L F, Froneman, P William, Callaghan, Amanda, Dick, Jaimie T A
- Authors: Cuthbert, Ross N , Dalu, Tatenda , Wasserman, Ryan J , Weyl, Olaf L F , Froneman, P William , Callaghan, Amanda , Dick, Jaimie T A
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/466946 , vital:76801 , https://doi.org/10.1111/een.12801
- Description: The strengths of trophic interactions within ecosystems can be mediated by complex mechanisms that require elucidation if researchers are to understand and predict population‐ and community‐level stabilities. Where multiple prey types co‐occur, prey switching (i.e. frequency‐dependent predation) by predators may facilitate low‐density prey refuge effects which promote coexistence. On the other hand, lack of switching and strong preferences by predators can strongly suppress prey populations, which is especially important considering vector species such as mosquitoes.
- Full Text:
- Date Issued: 2020
- Authors: Cuthbert, Ross N , Dalu, Tatenda , Wasserman, Ryan J , Weyl, Olaf L F , Froneman, P William , Callaghan, Amanda , Dick, Jaimie T A
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/466946 , vital:76801 , https://doi.org/10.1111/een.12801
- Description: The strengths of trophic interactions within ecosystems can be mediated by complex mechanisms that require elucidation if researchers are to understand and predict population‐ and community‐level stabilities. Where multiple prey types co‐occur, prey switching (i.e. frequency‐dependent predation) by predators may facilitate low‐density prey refuge effects which promote coexistence. On the other hand, lack of switching and strong preferences by predators can strongly suppress prey populations, which is especially important considering vector species such as mosquitoes.
- Full Text:
- Date Issued: 2020
Sex demographics alter the effect of habitat structure on predation by a temporary pond specialist
- Cuthbert, Ross N, Sithagu, Rotondwa, Weyl, Olaf L F, Froneman, P William, Wasserman, Ryan J, Dick, Jaimie T A, Callaghan, Amanda, Foord, Stefan, Dalu, Tatenda
- Authors: Cuthbert, Ross N , Sithagu, Rotondwa , Weyl, Olaf L F , Froneman, P William , Wasserman, Ryan J , Dick, Jaimie T A , Callaghan, Amanda , Foord, Stefan , Dalu, Tatenda
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/466968 , vital:76803 , https://doi.org/10.1016/j.limno.2020.125747
- Description: Habitat structure can profoundly influence interaction strengths between predators and prey. Spatio-temporal habitat structure in temporary wetland ecosystems is particularly variable because of fluctuations in water levels and vegetation colonisation dynamics. Demographic characteristics within animal populations may also alter the influence of habitat structure on biotic interactions, but have remained untested. Here, we investigate the influence of vegetation habitat structure on the consumption of larval mosquito prey by the calanoid copepod Lovenula raynerae, a temporary pond specialist. Increased habitat complexity reduced predation, and gravid female copepods were generally more voracious than male copepods in simplified habitats. However, sexes were more similar as habitat complexity increased. Type II functional responses were exhibited by the copepods irrespective of habitat complexity and sex, owing to consistent high prey acquisition at low prey densities. Attack rates by copepods were relatively unaffected by the complexity gradient, whilst handling times lengthened under more complex environments in gravid female copepods. We demonstrate emergent effects of habitat complexity across species demographics, with predation by males more robust to differences in habitat complexity than females. For ecosystems such as temporary ponds where sex-skewed predator ratios develop, our laboratory findings suggest habitat complexity and sex demographics mediate prey risk.
- Full Text:
- Date Issued: 2020
- Authors: Cuthbert, Ross N , Sithagu, Rotondwa , Weyl, Olaf L F , Froneman, P William , Wasserman, Ryan J , Dick, Jaimie T A , Callaghan, Amanda , Foord, Stefan , Dalu, Tatenda
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/466968 , vital:76803 , https://doi.org/10.1016/j.limno.2020.125747
- Description: Habitat structure can profoundly influence interaction strengths between predators and prey. Spatio-temporal habitat structure in temporary wetland ecosystems is particularly variable because of fluctuations in water levels and vegetation colonisation dynamics. Demographic characteristics within animal populations may also alter the influence of habitat structure on biotic interactions, but have remained untested. Here, we investigate the influence of vegetation habitat structure on the consumption of larval mosquito prey by the calanoid copepod Lovenula raynerae, a temporary pond specialist. Increased habitat complexity reduced predation, and gravid female copepods were generally more voracious than male copepods in simplified habitats. However, sexes were more similar as habitat complexity increased. Type II functional responses were exhibited by the copepods irrespective of habitat complexity and sex, owing to consistent high prey acquisition at low prey densities. Attack rates by copepods were relatively unaffected by the complexity gradient, whilst handling times lengthened under more complex environments in gravid female copepods. We demonstrate emergent effects of habitat complexity across species demographics, with predation by males more robust to differences in habitat complexity than females. For ecosystems such as temporary ponds where sex-skewed predator ratios develop, our laboratory findings suggest habitat complexity and sex demographics mediate prey risk.
- Full Text:
- Date Issued: 2020
Water volume differentially modifies copepod predatory strengths on two prey types
- Cuthbert, Ross N, Sithagu, Rotondwa, Weyl, Olaf L F, Froneman, P William, Wasserman, Ryan J, Dick, Jaimie T A, Callaghan, Amanda, Foord, Stefan, Dalu, Tatenda
- Authors: Cuthbert, Ross N , Sithagu, Rotondwa , Weyl, Olaf L F , Froneman, P William , Wasserman, Ryan J , Dick, Jaimie T A , Callaghan, Amanda , Foord, Stefan , Dalu, Tatenda
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/466979 , vital:76804 , https://doi.org/10.1016/j.limno.2020.125747
- Description: Predatory interaction strengths are highly context-dependent, and in temporary aquatic ecosystems, may be affected by water volume changes. We examine the influence of water volume on Lovenula raynerae (Copepoda) functional responses towards two temporary pond prey types. Daphnia prey risk was not affected by increasing water volume, whereas for Culex prey risk was reduced. Accordingly, water volume changes through the hydroperiod may have species-specific effects on prey, with implications for population persistence under environmental change.
- Full Text:
- Date Issued: 2020
- Authors: Cuthbert, Ross N , Sithagu, Rotondwa , Weyl, Olaf L F , Froneman, P William , Wasserman, Ryan J , Dick, Jaimie T A , Callaghan, Amanda , Foord, Stefan , Dalu, Tatenda
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/466979 , vital:76804 , https://doi.org/10.1016/j.limno.2020.125747
- Description: Predatory interaction strengths are highly context-dependent, and in temporary aquatic ecosystems, may be affected by water volume changes. We examine the influence of water volume on Lovenula raynerae (Copepoda) functional responses towards two temporary pond prey types. Daphnia prey risk was not affected by increasing water volume, whereas for Culex prey risk was reduced. Accordingly, water volume changes through the hydroperiod may have species-specific effects on prey, with implications for population persistence under environmental change.
- Full Text:
- Date Issued: 2020
Additive multiple predator effects of two specialist paradiaptomid copepods towards larval mosquitoes
- Cuthbert, Ross N, Dalu, Tatenda, Wasserman, Ryan J, Weyl, Olaf L F, Froneman, P William, Callaghan, Amanda, Dick, Jaimie T A
- Authors: Cuthbert, Ross N , Dalu, Tatenda , Wasserman, Ryan J , Weyl, Olaf L F , Froneman, P William , Callaghan, Amanda , Dick, Jaimie T A
- Date: 2019
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/467137 , vital:76828 , https://doi.org/10.1016/j.limno.2019.125727
- Description: Interactions between multiple predators can profoundly affect prey risk, with implications for prey population stability and ecosystem functioning. In austral temporary wetlands, arid-area adapted specialist copepods are key predators for much of the hydroperiod. Limited autoecological information relating to species interactions negates understandings of trophic dynamics in these systems. In the present study, we examined multiple predator effects of two key predatory paradiaptomid copepods which often coexist in austral temporary wetlands, Lovenula raynerae Suárez-Morales, Wasserman and Dalu 2015 and Paradiaptomus lamellatus Sars, 1985. Predation rates towards larval mosquito prey across different water depths were quantified.
- Full Text:
- Date Issued: 2019
- Authors: Cuthbert, Ross N , Dalu, Tatenda , Wasserman, Ryan J , Weyl, Olaf L F , Froneman, P William , Callaghan, Amanda , Dick, Jaimie T A
- Date: 2019
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/467137 , vital:76828 , https://doi.org/10.1016/j.limno.2019.125727
- Description: Interactions between multiple predators can profoundly affect prey risk, with implications for prey population stability and ecosystem functioning. In austral temporary wetlands, arid-area adapted specialist copepods are key predators for much of the hydroperiod. Limited autoecological information relating to species interactions negates understandings of trophic dynamics in these systems. In the present study, we examined multiple predator effects of two key predatory paradiaptomid copepods which often coexist in austral temporary wetlands, Lovenula raynerae Suárez-Morales, Wasserman and Dalu 2015 and Paradiaptomus lamellatus Sars, 1985. Predation rates towards larval mosquito prey across different water depths were quantified.
- Full Text:
- Date Issued: 2019
Combined impacts of warming and salinisation on trophic interactions and mortality of a specialist ephemeral wetland predator
- Cuthbert, Ross N, Weyl, Olaf L F, Wasserman, Ryan J, Dick, Jaimie T A, Froneman, P William, Callaghan, Amanda, Dalu, Tatenda
- Authors: Cuthbert, Ross N , Weyl, Olaf L F , Wasserman, Ryan J , Dick, Jaimie T A , Froneman, P William , Callaghan, Amanda , Dalu, Tatenda
- Date: 2019
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/467160 , vital:76832 , https://doi.org/10.1111/fwb.13353
- Description: Wetlands are of enormous importance for biodiversity globally but are under increasing risk from multiple stressors driven by ongoing anthro-pogenic environmental change. As the trophic structure and dynamics of ephemeral wetlands are poorly understood, it is difficult to predict how these biodiverse ecosystems will be impacted by global change. In particular, warming and salinisation are projected to have profound im-pacts on these wetlands in future. The present study examined the combined effects of warming and salinisation on species interaction strengths and mortality rates for two ephemeral wetland species. Using an ephemeral pond specialist copepod, Lovenula raynerae Suárez‐Morales, Wasserman, and Dalu, (2015) as a model predator species, we applied a functional response approach to derive warming and salinisa-tion effects on trophic interactions with a prey species. Furthermore, the effects of a salinisation gradient on mortality rates of adult copepods were quantified.
- Full Text:
- Date Issued: 2019
- Authors: Cuthbert, Ross N , Weyl, Olaf L F , Wasserman, Ryan J , Dick, Jaimie T A , Froneman, P William , Callaghan, Amanda , Dalu, Tatenda
- Date: 2019
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/467160 , vital:76832 , https://doi.org/10.1111/fwb.13353
- Description: Wetlands are of enormous importance for biodiversity globally but are under increasing risk from multiple stressors driven by ongoing anthro-pogenic environmental change. As the trophic structure and dynamics of ephemeral wetlands are poorly understood, it is difficult to predict how these biodiverse ecosystems will be impacted by global change. In particular, warming and salinisation are projected to have profound im-pacts on these wetlands in future. The present study examined the combined effects of warming and salinisation on species interaction strengths and mortality rates for two ephemeral wetland species. Using an ephemeral pond specialist copepod, Lovenula raynerae Suárez‐Morales, Wasserman, and Dalu, (2015) as a model predator species, we applied a functional response approach to derive warming and salinisa-tion effects on trophic interactions with a prey species. Furthermore, the effects of a salinisation gradient on mortality rates of adult copepods were quantified.
- Full Text:
- Date Issued: 2019
Macroinvertebrate functional feeding group alterations in response to habitat degradation of headwater Austral streams
- Mangadze, Tinotenda, Wasserman, Ryan J, Froneman, P William, Dalu, Tatenda
- Authors: Mangadze, Tinotenda , Wasserman, Ryan J , Froneman, P William , Dalu, Tatenda
- Date: 2019
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/467211 , vital:76840 , https://doi.org/10.1016/j.scitotenv.2019.133910
- Description: Protecting the structural and functional integrity of lotic ecosystems is becoming increasingly important as many ecological systems face escalating pressures from human population growth and environmental impacts. Knowledge on the functional composition of macroinvertebrates in austral temperate streams is generally lacking hindering the design and implementation of water management and restoration goals. Therefore, this study examined the effects of urban land–use activities on the benthic macroinvertebrate functional feeding guild structure among different stream orders in an austral river system (Bloukrans River) in the Eastern Cape Province of South Africa. Water quality and macroinvertebrate community data were collected across two seasons from 18 sites in two different stream order categories (i.e. 1, 2 + 3), following standard methods. We separated macroinvertebrates into functional feeding groups (FFGs), which we then used to assess the effects of riparian condition on FFG organization. Linear mixed effects model (LMM) results demonstrated that total dissolved solids (TDS), canopy cover, phosphate and channel width were the key variables that described the major sources of variation in macroinvertebrate FFGs.
- Full Text:
- Date Issued: 2019
- Authors: Mangadze, Tinotenda , Wasserman, Ryan J , Froneman, P William , Dalu, Tatenda
- Date: 2019
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/467211 , vital:76840 , https://doi.org/10.1016/j.scitotenv.2019.133910
- Description: Protecting the structural and functional integrity of lotic ecosystems is becoming increasingly important as many ecological systems face escalating pressures from human population growth and environmental impacts. Knowledge on the functional composition of macroinvertebrates in austral temperate streams is generally lacking hindering the design and implementation of water management and restoration goals. Therefore, this study examined the effects of urban land–use activities on the benthic macroinvertebrate functional feeding guild structure among different stream orders in an austral river system (Bloukrans River) in the Eastern Cape Province of South Africa. Water quality and macroinvertebrate community data were collected across two seasons from 18 sites in two different stream order categories (i.e. 1, 2 + 3), following standard methods. We separated macroinvertebrates into functional feeding groups (FFGs), which we then used to assess the effects of riparian condition on FFG organization. Linear mixed effects model (LMM) results demonstrated that total dissolved solids (TDS), canopy cover, phosphate and channel width were the key variables that described the major sources of variation in macroinvertebrate FFGs.
- Full Text:
- Date Issued: 2019
Quantifying reproductive state and predator effects on copepod motility in ephemeral ecosystems
- Cuthbert, Ross N, Dalu, Tatenda, Wasserman, Ryan J, Dick, Jaimie T A, Callaghan, Amanda, Froneman, P William, Weyl, Olaf L F
- Authors: Cuthbert, Ross N , Dalu, Tatenda , Wasserman, Ryan J , Dick, Jaimie T A , Callaghan, Amanda , Froneman, P William , Weyl, Olaf L F
- Date: 2019
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/467171 , vital:76836 , https://doi.org/10.1016/j.jaridenv.2019.05.010
- Description: Ephemeral wetlands in arid environments are unique ecosystems with atypical trophic structuring, often dominated by invertebrate predation. Copepod behavioural traits and vulnerabilities to predation can vary substantially according to reproductive status. Gravid female copepods may be more vulnerable to predation due to reduced escape speeds or higher visibility to predators. Here, we quantify how reproductive status modulates horizontal motility rates of the predatory ephemeral pond specialist copepod Lovenula raynerae, and the responsiveness of the copepod to predator cues of the notonectid Anisops debilis. Males exhibited significantly higher motility rates than gravid female copepods, however chemical predator cues did not significantly influence activity rates in either sex. The lack of responsiveness to predator cues by specialist copepods in ephemeral wetlands may result from a lack of predation pressure in these systems, or due to time stress to reproduce during short hydroperiods. In turn, this could increase predation risk to copepods from externally-recruited top predators in ephemeral wetlands, and potentially contribute to the development of skewed sex ratios in favour of females.
- Full Text:
- Date Issued: 2019
- Authors: Cuthbert, Ross N , Dalu, Tatenda , Wasserman, Ryan J , Dick, Jaimie T A , Callaghan, Amanda , Froneman, P William , Weyl, Olaf L F
- Date: 2019
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/467171 , vital:76836 , https://doi.org/10.1016/j.jaridenv.2019.05.010
- Description: Ephemeral wetlands in arid environments are unique ecosystems with atypical trophic structuring, often dominated by invertebrate predation. Copepod behavioural traits and vulnerabilities to predation can vary substantially according to reproductive status. Gravid female copepods may be more vulnerable to predation due to reduced escape speeds or higher visibility to predators. Here, we quantify how reproductive status modulates horizontal motility rates of the predatory ephemeral pond specialist copepod Lovenula raynerae, and the responsiveness of the copepod to predator cues of the notonectid Anisops debilis. Males exhibited significantly higher motility rates than gravid female copepods, however chemical predator cues did not significantly influence activity rates in either sex. The lack of responsiveness to predator cues by specialist copepods in ephemeral wetlands may result from a lack of predation pressure in these systems, or due to time stress to reproduce during short hydroperiods. In turn, this could increase predation risk to copepods from externally-recruited top predators in ephemeral wetlands, and potentially contribute to the development of skewed sex ratios in favour of females.
- Full Text:
- Date Issued: 2019
River nutrient water and sediment measurements inform on nutrient retention, with implications for eutrophication
- Dalu, Tatenda, Wasserman, Ryan J, Magoro, Mandla L, Froneman, P William, Weyl, Olaf, L F
- Authors: Dalu, Tatenda , Wasserman, Ryan J , Magoro, Mandla L , Froneman, P William , Weyl, Olaf, L F
- Date: 2019
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/467222 , vital:76841 , https://doi.org/10.1016/j.scitotenv.2019.05.167
- Description: The consideration of nutrients in pollution dynamics is important for environmental management and conservation. Developing countries are yet to appreciate the aquatic ecosystem pollution impacts on their economies and as such, information on water pollution dynamics is limited. This study assessed the spatio-temporal dynamics of nutrient loading and retention in stream water and sediments in the Bloukrans River system, Eastern Cape province, South Africa over the course of the wet and dry season. Sediment and water samples were analysed for total phosphorus (TP) and nitrogen (TN) concentrations, and were used in combination with river flow discharge, to determine nutrient loads. The study results highlight that river discharge plays a significant role in temporal differences in sediment and water column nutrient concentrations.
- Full Text:
- Date Issued: 2019
- Authors: Dalu, Tatenda , Wasserman, Ryan J , Magoro, Mandla L , Froneman, P William , Weyl, Olaf, L F
- Date: 2019
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/467222 , vital:76841 , https://doi.org/10.1016/j.scitotenv.2019.05.167
- Description: The consideration of nutrients in pollution dynamics is important for environmental management and conservation. Developing countries are yet to appreciate the aquatic ecosystem pollution impacts on their economies and as such, information on water pollution dynamics is limited. This study assessed the spatio-temporal dynamics of nutrient loading and retention in stream water and sediments in the Bloukrans River system, Eastern Cape province, South Africa over the course of the wet and dry season. Sediment and water samples were analysed for total phosphorus (TP) and nitrogen (TN) concentrations, and were used in combination with river flow discharge, to determine nutrient loads. The study results highlight that river discharge plays a significant role in temporal differences in sediment and water column nutrient concentrations.
- Full Text:
- Date Issued: 2019
Sacrificial males the potential role of copulation and predation in contributing to copepod sex-skewed ratios
- Wasserman, Ryan J, Weston, Mark, Weyl, Olaf, L F, Froneman, P William, Welch, Rebecca J, Vink, Tim J F, Dalu, Tatenda
- Authors: Wasserman, Ryan J , Weston, Mark , Weyl, Olaf, L F , Froneman, P William , Welch, Rebecca J , Vink, Tim J F , Dalu, Tatenda
- Date: 2018
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/467233 , vital:76843 , https://doi.org/10.1111/oik.04832
- Description: Predation is thought to play a selective role in the emergence of behavioural traits in prey. Differences in behaviour between prey demographics may, therefore, be driven by predation with select components of the population being less vulnerable to predators. While under controlled conditions prey demography has been shown to have consequences for predation success, investigations linking these implications to natural prey population demographics are scarce. Here we assess predator–prey dynamics between notonectid predators (backswimmers) and Lovenula raynerae (Copepoda), key faunal groups in temperate ephemeral pond ecosystems. Using a combination of field and experimental approaches we test for the development and mechanism of predation‐induced sex‐skewed ratios. A natural population of L. raynerae was tracked over time in relation to their predator (notonectid) and prey (Cladocera) numbers. In the laboratory, L. raynerae sex ratios were also assessed over time but in the absence of predation pressure.
- Full Text:
- Date Issued: 2018
- Authors: Wasserman, Ryan J , Weston, Mark , Weyl, Olaf, L F , Froneman, P William , Welch, Rebecca J , Vink, Tim J F , Dalu, Tatenda
- Date: 2018
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/467233 , vital:76843 , https://doi.org/10.1111/oik.04832
- Description: Predation is thought to play a selective role in the emergence of behavioural traits in prey. Differences in behaviour between prey demographics may, therefore, be driven by predation with select components of the population being less vulnerable to predators. While under controlled conditions prey demography has been shown to have consequences for predation success, investigations linking these implications to natural prey population demographics are scarce. Here we assess predator–prey dynamics between notonectid predators (backswimmers) and Lovenula raynerae (Copepoda), key faunal groups in temperate ephemeral pond ecosystems. Using a combination of field and experimental approaches we test for the development and mechanism of predation‐induced sex‐skewed ratios. A natural population of L. raynerae was tracked over time in relation to their predator (notonectid) and prey (Cladocera) numbers. In the laboratory, L. raynerae sex ratios were also assessed over time but in the absence of predation pressure.
- Full Text:
- Date Issued: 2018
Trophic isotopic carbon variation increases with pond’s hydroperiod: evidence from an Austral ephemeral ecosystem
- Dalu, Tatenda, Wasserman, Ryan J, Froneman, P William, Weyl, Olaf, L F
- Authors: Dalu, Tatenda , Wasserman, Ryan J , Froneman, P William , Weyl, Olaf, L F
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/467244 , vital:76844 , https://doi.org/10.1038/s41598-017-08026-6
- Description: Trophic variation in food web structure occurs among and within ecosystems. The magnitude of variation, however, differs from system to system. In ephemeral pond ecosystems, temporal dynamics are relatively more important than in many systems given that hydroperiod is the ultimate factor determining the presence of an aquatic state. Here, using stable isotopes we tested for changes in trophic chain length and shape over time in these dynamic aquatic ecosystems. We found that lower and intermediate trophic level structure increased over time. We discuss these findings within the context of temporal environmental stability. The dynamic nature of these ephemeral systems seems to be conducive to greater levels of intermediate and lower trophic level diversity, with omnivorous traits likely being advantageous.
- Full Text:
- Date Issued: 2017
- Authors: Dalu, Tatenda , Wasserman, Ryan J , Froneman, P William , Weyl, Olaf, L F
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/467244 , vital:76844 , https://doi.org/10.1038/s41598-017-08026-6
- Description: Trophic variation in food web structure occurs among and within ecosystems. The magnitude of variation, however, differs from system to system. In ephemeral pond ecosystems, temporal dynamics are relatively more important than in many systems given that hydroperiod is the ultimate factor determining the presence of an aquatic state. Here, using stable isotopes we tested for changes in trophic chain length and shape over time in these dynamic aquatic ecosystems. We found that lower and intermediate trophic level structure increased over time. We discuss these findings within the context of temporal environmental stability. The dynamic nature of these ephemeral systems seems to be conducive to greater levels of intermediate and lower trophic level diversity, with omnivorous traits likely being advantageous.
- Full Text:
- Date Issued: 2017
Variation partitioning of benthic diatom community matrices: Effects of multiple variables on benthic diatom communities in an Austral temperate river system
- Dalu, Tatenda, Wasserman, Ryan J, Magoro, Mandla L, Mwedzi, Tongayi, Froneman, P William, Weyl, Olaf L F
- Authors: Dalu, Tatenda , Wasserman, Ryan J , Magoro, Mandla L , Mwedzi, Tongayi , Froneman, P William , Weyl, Olaf L F
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/467182 , vital:76837 , https://doi.org/10.1016/j.scitotenv.2017.05.162
- Description: This study explores diatom community dynamics in a highly modified semi-arid temperate region river system characterised by inconsistent river flow. Various water and sediment environmental variables were assessed using a multi-faceted analysis approach to determine the spatio-temporal drivers of benthic diatom communities in the river system. Overall, the diatom community was generally dominated by pollution tolerant species, reflecting the anthropogenic intensity and activities on the river system. Diatom community composition was found to be largely determined by water column chemistry variables particularly nutrient concentrations in comparison to sediment chemistry and physical variables. Strong seasonal diatom species composition was also observed and this was driven by strong seasonal variations in nutrient loads and metal concentrations, a result of the variable water flow across the two seasons. However, the greater temporal variation in communities was observed in the smaller systems with the mainstream river system being more homogenous over time. In addition, diatom community composition and environmental variables were found to be different and more pronounced between streams and mainstream sites, than between canals and streams. The study highlights the complex interaction between water column, sediment and physical variables in determining the diatom species composition in small river systems. It also highlights the importance of river flow inconsistency as an indirect variable that alters primary drivers such as nutrient concentrations in the water column and heavy metal levels in the sediment.
- Full Text:
- Date Issued: 2017
- Authors: Dalu, Tatenda , Wasserman, Ryan J , Magoro, Mandla L , Mwedzi, Tongayi , Froneman, P William , Weyl, Olaf L F
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/467182 , vital:76837 , https://doi.org/10.1016/j.scitotenv.2017.05.162
- Description: This study explores diatom community dynamics in a highly modified semi-arid temperate region river system characterised by inconsistent river flow. Various water and sediment environmental variables were assessed using a multi-faceted analysis approach to determine the spatio-temporal drivers of benthic diatom communities in the river system. Overall, the diatom community was generally dominated by pollution tolerant species, reflecting the anthropogenic intensity and activities on the river system. Diatom community composition was found to be largely determined by water column chemistry variables particularly nutrient concentrations in comparison to sediment chemistry and physical variables. Strong seasonal diatom species composition was also observed and this was driven by strong seasonal variations in nutrient loads and metal concentrations, a result of the variable water flow across the two seasons. However, the greater temporal variation in communities was observed in the smaller systems with the mainstream river system being more homogenous over time. In addition, diatom community composition and environmental variables were found to be different and more pronounced between streams and mainstream sites, than between canals and streams. The study highlights the complex interaction between water column, sediment and physical variables in determining the diatom species composition in small river systems. It also highlights the importance of river flow inconsistency as an indirect variable that alters primary drivers such as nutrient concentrations in the water column and heavy metal levels in the sediment.
- Full Text:
- Date Issued: 2017
Emergent effects of structural complexity and temperature on predator–prey interactions
- Wasserman, Ryan J, Alexander, Mhairi E, Weyl, Olaf L F, Barrios‐O'Neill, Daniel, Froneman, P William, Dalu, Tatenda
- Authors: Wasserman, Ryan J , Alexander, Mhairi E , Weyl, Olaf L F , Barrios‐O'Neill, Daniel , Froneman, P William , Dalu, Tatenda
- Date: 2016
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/69190 , vital:29444 , https://doi.org/10.1002/ecs2.1239
- Description: Ephemeral aquatic environments are important habitats for a variety of species. They are highly variable with regards to vegetation structure and physico‐chemical features that potentially mediate outcomes of biotic interactions. Multiple environmental variables and their emergent impacts on the relationship between prey consumption rate by a predator and prey density (functional response), however, are rarely assessed. Here, we investigated the combined effects of temperature and habitat complexity on the functional response of the freshwater predatory notonectid Enithares sobria on the cladoceran prey organism Daphnia longispina. A Type II functional response was observed for E. sobria predating on D. longispina and while temperature and habitat complexity had no effect on the response type, these environmental variables interacted with consequences for the magnitude of the functional responses. Overall, structural complexity favored the predator as greater consumption was observed in the most complex habitat treatment. Temperature effects were also evident although these effects were not unidirectional with regard to treatment factor gradients as predators were the most successful at intermediary temperatures. Furthermore, there was a complex interplay between habitat complexity and temperature, with attack rates being greatest at low and high complexities within intermediate temperatures, while at zero complexity attack rates were greatest at the lowest temperature. The effect of habitat on handling times was only evident in the low temperature treatments which decreased steadily with each increase in complexity. Through the application of functional responses the synergistic effects of multiple environmental drivers on predator–prey interaction outcomes have been highlighted, adding insight into how interactions among species may be affected by natural or artificially induced environmental variability.
- Full Text:
- Date Issued: 2016
- Authors: Wasserman, Ryan J , Alexander, Mhairi E , Weyl, Olaf L F , Barrios‐O'Neill, Daniel , Froneman, P William , Dalu, Tatenda
- Date: 2016
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/69190 , vital:29444 , https://doi.org/10.1002/ecs2.1239
- Description: Ephemeral aquatic environments are important habitats for a variety of species. They are highly variable with regards to vegetation structure and physico‐chemical features that potentially mediate outcomes of biotic interactions. Multiple environmental variables and their emergent impacts on the relationship between prey consumption rate by a predator and prey density (functional response), however, are rarely assessed. Here, we investigated the combined effects of temperature and habitat complexity on the functional response of the freshwater predatory notonectid Enithares sobria on the cladoceran prey organism Daphnia longispina. A Type II functional response was observed for E. sobria predating on D. longispina and while temperature and habitat complexity had no effect on the response type, these environmental variables interacted with consequences for the magnitude of the functional responses. Overall, structural complexity favored the predator as greater consumption was observed in the most complex habitat treatment. Temperature effects were also evident although these effects were not unidirectional with regard to treatment factor gradients as predators were the most successful at intermediary temperatures. Furthermore, there was a complex interplay between habitat complexity and temperature, with attack rates being greatest at low and high complexities within intermediate temperatures, while at zero complexity attack rates were greatest at the lowest temperature. The effect of habitat on handling times was only evident in the low temperature treatments which decreased steadily with each increase in complexity. Through the application of functional responses the synergistic effects of multiple environmental drivers on predator–prey interaction outcomes have been highlighted, adding insight into how interactions among species may be affected by natural or artificially induced environmental variability.
- Full Text:
- Date Issued: 2016
Trophic interactions in an austral temperate ephemeral pond inferred using stable isotope analysis
- Dalu, Tatenda, Weyl, Olaf L F, Froneman, P William, Wasserman, Ryan J
- Authors: Dalu, Tatenda , Weyl, Olaf L F , Froneman, P William , Wasserman, Ryan J
- Date: 2016
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/68022 , vital:29185 , https://doi.org/10.1007/s10750-015-2533-5
- Description: Publisher version , Ephemeral ponds are vulnerable aquatic habitats which are difficult to protect given their dynamic nature and sensitivity to degradation during dry periods. Little information is available on these habitats in austral regions, with almost no information on food-web structure and complexity. The study aimed to assess trophic interactions among dominant organisms in an ephemeral pond food web, and investigate the importance of autochthonous and allochthonous carbon, using 13C and 15N isotopes. Results of the investigation suggest that the food web comprised four trophic levels, with the top predators being Notonectids (Notonecta sp.) and diving beetles (Cybister tripunctatus (Olivier)). Intermediary trophic levels comprised zooplankton (daphniids and copepodids), macroinvertebrates (e.g. micronectids and molluscs) and tadpoles. Generalist feeders dominated the higher trophic levels (>3) with specialists comprising the lower trophic levels (≤3). The consumers preferred autochthonous fine particulate organic matter, epiphyton and submerged macrophyte organic matter sources over allochthonous sources. Autochthonous organic matter was transferred to the food web via zooplankton and select macroinvertebrates including Micronecta sp. and Physa sp. The food-web structure within the pond appeared to reflect the secondary stage of trophic structural complexity in the evolution of ephemeral ponds over the course of their hydro-period.
- Full Text: false
- Date Issued: 2016
- Authors: Dalu, Tatenda , Weyl, Olaf L F , Froneman, P William , Wasserman, Ryan J
- Date: 2016
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/68022 , vital:29185 , https://doi.org/10.1007/s10750-015-2533-5
- Description: Publisher version , Ephemeral ponds are vulnerable aquatic habitats which are difficult to protect given their dynamic nature and sensitivity to degradation during dry periods. Little information is available on these habitats in austral regions, with almost no information on food-web structure and complexity. The study aimed to assess trophic interactions among dominant organisms in an ephemeral pond food web, and investigate the importance of autochthonous and allochthonous carbon, using 13C and 15N isotopes. Results of the investigation suggest that the food web comprised four trophic levels, with the top predators being Notonectids (Notonecta sp.) and diving beetles (Cybister tripunctatus (Olivier)). Intermediary trophic levels comprised zooplankton (daphniids and copepodids), macroinvertebrates (e.g. micronectids and molluscs) and tadpoles. Generalist feeders dominated the higher trophic levels (>3) with specialists comprising the lower trophic levels (≤3). The consumers preferred autochthonous fine particulate organic matter, epiphyton and submerged macrophyte organic matter sources over allochthonous sources. Autochthonous organic matter was transferred to the food web via zooplankton and select macroinvertebrates including Micronecta sp. and Physa sp. The food-web structure within the pond appeared to reflect the secondary stage of trophic structural complexity in the evolution of ephemeral ponds over the course of their hydro-period.
- Full Text: false
- Date Issued: 2016
An Assessment of the Effect of Rotenone on Selected Non-Target Aquatic Fauna
- Dalu, Tatenda, Wasserman, Ryan J, Jordaan, Martine, Froneman, P William, Weyl, Olaf L F
- Authors: Dalu, Tatenda , Wasserman, Ryan J , Jordaan, Martine , Froneman, P William , Weyl, Olaf L F
- Date: 2015
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124240 , vital:35579 , https://doi.org/10.1371/journal.pone.0142140.g001
- Description: Rotenone, a naturally occurring ketone, is widely employed for the management of invasive fish species. The use of rotenone poses serious challenges to conservation practitioners due to its impacts on non-target organisms including amphibians and macroinvertebrates. Using laboratory studies, we investigated the effects of different rotenone concentrations (0, 12.5, 25, 37.5, 50, 100 μg L-1) on selected invertebrate groups; Aeshnidae, Belostomatids, Decapods, Ephemeroptera, Pulmonata and zooplankton over a period of 18 hours. Based on field observations and body size, we hypothesized that Ephemeropterans and zooplank- ton would be more susceptible to rote none than Decapods, Belostomatids and snails. Experimental results supported this hypothesis and mortality and behaviour effects varied considerably between taxa, ranging from no effect (crab Potamonuates sidneyi) to 100% mortality (Daphnia pulex and Paradiaptomus lamellatus). Planktonic invertebrates were par- ticularly sensitive to rotenone even at very low concentrations. Future research should investigate the recovery time of invertebrate communities after the application of rotenone and conduct field assessments assessing the longer term effects of rotenone exposure on the population dynamics of those less sensitive organisms.
- Full Text:
- Date Issued: 2015
- Authors: Dalu, Tatenda , Wasserman, Ryan J , Jordaan, Martine , Froneman, P William , Weyl, Olaf L F
- Date: 2015
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124240 , vital:35579 , https://doi.org/10.1371/journal.pone.0142140.g001
- Description: Rotenone, a naturally occurring ketone, is widely employed for the management of invasive fish species. The use of rotenone poses serious challenges to conservation practitioners due to its impacts on non-target organisms including amphibians and macroinvertebrates. Using laboratory studies, we investigated the effects of different rotenone concentrations (0, 12.5, 25, 37.5, 50, 100 μg L-1) on selected invertebrate groups; Aeshnidae, Belostomatids, Decapods, Ephemeroptera, Pulmonata and zooplankton over a period of 18 hours. Based on field observations and body size, we hypothesized that Ephemeropterans and zooplank- ton would be more susceptible to rote none than Decapods, Belostomatids and snails. Experimental results supported this hypothesis and mortality and behaviour effects varied considerably between taxa, ranging from no effect (crab Potamonuates sidneyi) to 100% mortality (Daphnia pulex and Paradiaptomus lamellatus). Planktonic invertebrates were par- ticularly sensitive to rotenone even at very low concentrations. Future research should investigate the recovery time of invertebrate communities after the application of rotenone and conduct field assessments assessing the longer term effects of rotenone exposure on the population dynamics of those less sensitive organisms.
- Full Text:
- Date Issued: 2015