Habitat simplification increases the impact of a freshwater invasive fish
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Biodiversity continues to decline at a range of spatial scales and there is an urgent requirement to understand how multiple drivers interact in causing such declines. Further, we require methodologies that can facilitate predictions of the effects of such drivers in the future. Habitat degradation and biological invasions are two of the most important threats to biodiversity and here we investigate their combined effects, both in terms of understanding and predicting impacts on native species. The predatory largemouth bass Micropterus salmoides is one of the World’s Worst Invaders, causing declines in native prey species, and its introduction often coincides with habitat simplification. We investigated the predatory functional response, as a measure of ecological impact, of juvenile largemouth bass in artificial vegetation over a range of habitat complexities (high, intermediate, low and zero). Prey, the female guppy Poecilia reticulata, were representative of native fish. As habitats became less complex, significantly more prey were consumed, since, even although attack rates declined, reduced handling times resulted in higher maximum feeding rates by bass. At all levels of habitat complexity, bass exhibited potentially population de-stabilising Type II functional responses, with no emergence of more stabilising Type III functional responses as often occurs in predator-prey relationships in complex habitats. Thus, habitat degradation and simplification potentially exacerbate the impact of this invasive species, but even highly complex habitats may ultimately not protect native species. The utilisation of functional responses under varying environmental contexts provides a method for the understanding and prediction of invasive species impacts.
KeywordsHabitat complexity Invasive species Functional response Impact Global change Freshwater fish
We thank K. van der Walt, N. Songongo, G. Taylor, A. Luger, B. Ellender, D. Howell, C. Hoek, Y. Omardien, M. Pegg, B. Dredge, L. Mofu, P. Weyl and O. Weyl for technical and logistical support, including field collections. This research was funded by the DST-NRF Centre of Excellence for Invasion Biology. DMR received support from the National Research Foundation (grant 85,417). The Department of Economic Development, Environmental Affairs and Tourism (Cacadu Region) is thanked for issuing research permits (4/13CR & 5/13CR). JD acknowledges support from NERC and the Leverhulme Trust.
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