COS 219-1 - Trophic disruption by an invasive species alters spatiotemporal food-web dynamics and energy fluxes

Abstract: The Trophic Disruption Hypothesis (TDH) predicts that invasive species cause native species to undergo trophic dispersion (change in trophic-niche size) and trophic displacement (diet switching), predictably altering food-web structure and biodiversity. African Jewelfish (Hemichromis letourneuxi) densities have recently increased greatly, resulting in declines of native taxa in Everglades National Park, USA. We used complementary datasets of stomach contents and stable isotopes (δ¹⁵N and δ¹³C) to quantify pre- and post-invasion consumer diets, trophic positions, trophic niches, and basal energy use (autotrophic vs heterotrophic) to test the TDH. Additionally, we calculated pre- and post-invasion energy fluxes among trophic guilds. Our findings support the TDH. Comparing pre- vs post-invasion data for native-species size classes, we observed trophic displacement in nearly half, trophic dispersion for most, few shifts in trophic position (mostly decreases), and greater reliance on autotrophic energy overall. Post-invasion trophic shifts among habitats and between seasons occurred at a similar frequency but greater magnitude than pre-invasion. Post-invasion food-web structure and function revealed increased relative abundances of mesopredators (including African Jewelfish) and reduced biomass and energy fluxes into and out of small fishes (e.g., Cyprinodontiformes). African Jewelfish invasion altered spatiotemporal trophic dynamics and energy fluxes through declines in native fishes and invertebrates, which indirectly affected trophic relationships at the regional scale in the Everglades. As a result, we suggest extending the TDH to explicitly include the potential for invasive species to alter basal-energy use, spatiotemporal trophic dynamics, and energy fluxes.