Abstract
Shifts in temperature as a result of climate change play an important role in the long-term dynamics of resource use and resulting species interactions. Functional responses can give ecologically relevant insights of context-specific density-dependent resource use with low intensity animal use. This is especially useful when working with vulnerable species. The Rondegat River in South Africa’s Cape Fold Ecoregion (CFE) was subjected to an invasive species removal program and although the threatened cyprinid populations are in a state of recovery, they are still at risk from abiotic stressors. This community is characterised by an oligotrophic environment, shared ancestry and spatial overlap, suggesting high food resource competition between species. Functional responses of two cyprinid species were compared between two prey types (mosquito and chironomid larvae) at different field-representative temperatures (18 °C and 25 °C) in laboratory trials, with the aim to infer response and resilience to global change. Labeobarbus seeberi consistently outperformed Sedercypris calidus across prey types and temperature treatments at high prey densities. This was driven primarily by shorter handling times in L. seeberi, despite higher attack parameters in S. calidus under certain prey/temperature scenarios. Temperature increase had differential effects on prey consumption dependent on fish species and prey type. However, neither species showed significant intraspecific differences in functional response between temperature conditions for either prey species, indicating community resilience to thermal change in the CFE. Context-dependent experiments can be used in tandem with field data to identify conditions of potential ecological tipping points in imperilled systems.
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The raw data generated and used in the analysis will be publicly available at the Knowledge Network for Biocomplexity (knb.ecoinformatics.org), URL: urn:uuid:29674dde-0b53-4434-be2e-52cf93f7b191.
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Acknowledgements
This study is dedicated to the memory of Professor Olaf Weyl, whose guidance and devotion to South African freshwater ecology made the Rondegat River restoration project and all work flowing therefrom possible. Permission for land access was granted by local conservation authority CapeNature and private land owners. This study was funded by the National Research Foundation (NRF)—South African Research Chairs Initiative of the Department of Science and Innovation (DSI) (Grant No. 110507) and JS acknowledges support from the DSI-NRF Centre of Excellence for Invasion Biology (CIB). Opinions expressed and conclusions arrived at are those of the author and are not necessarily to be attributed to the NRF. We hereby acknowledge the use of equipment provided by the NRF-SAIAB Marine Remote Imagery Platform and the funding channelled through the NRF-SAIAB Institutional Support System. We acknowledge CapeNature for facilitating our research activities in the Cederberg Wilderness Area. Jannie and Cecile Nieuwoudt (of Keurbos farm), and Jannie and Katrin Nieuwoudt (Grootkloof/Jamaka farms) are thanked for land access. Angus van Wyk assisted in the field; Munetsi Zvavahera and Takudzwa Madzivanzira assisted in the lab and during prey collection.
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The primary author was supported by the National Research Foundation (NRF)—South African Research Chairs Initiative of the Department of Science and Innovation (DSI) Grant no. 110507.
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CJB, JS and OLFW conceived the ideas and designed methodology; CJB collected the data; CJB and JS analysed the data; CJB led the writing of the manuscript. All authors contributed critically to the drafts and gave final approval for publication.
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This study was governed by CapeNature permit CN44-28–8357, CN16-28–8540, the Department of Economic Development, Environmental Affairs and Tourism (DEDEAT) permit CRO 124/19CR and TOPS permit 029705. Permission for land access was granted by CapeNature and private land owners where applicable. The experimental work was approved by the Rhodes University Animal Ethics Committee (reference numbers DIFS2118 and 2020–2815-4859) and the SAIAB Animal Ethics Committee (reference number 25/4/1/5_2018-10).
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Broom, C.J., South, J. & Weyl, O.L.F. Prey type and temperature influence functional responses of threatened endemic Cape Floristic Ecoregion fishes. Environ Biol Fish 104, 797–810 (2021). https://doi.org/10.1007/s10641-021-01111-w
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DOI: https://doi.org/10.1007/s10641-021-01111-w