Prey type and temperature influence functional responses of threatened endemic Cape Floristic Ecoregion fishes

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