Fish and Zooplankton Co-Responses to Environmental Gradients Under Different Climate Change Scenarios

Climate change is reshaping freshwater ecosystems worldwide, yet the extent to which its effects differ across trophic levels remains poorly understood. Despite growing evidence of community restructuring, few studies have jointly examined how multiple trophic levels respond to climate forcing within a functional and network-based framework. Herein, we assessed how fish and zooplankton communities respond to contemporary and projected end-of-century climate conditions using different shared socioeconomic pathways (SSP1-2.6, SSP3-7.0, and SSP5-8.5). By means of joint species distribution models and ecological network analyses, we examined fish-zooplankton co-responses to environmental gradients, quantified trait-environment relationships, and evaluated potential species interactions. We found that fish and zooplankton displayed distinct community and functional responses to current and projected climate gradients. Although both trophic levels were primarily influenced by climatic variables, fish exhibited stronger trait-climate relationships, including declining body size and increasing thermal tolerance with warming. Through ecological network analyses, we then demonstrated that freshwater communities tended to become more homogenized by 2100 under future climate change. Together, these results suggest contrasting climate sensitivities across trophic levels, potentially leading to trophic decoupling and functional reorganization of freshwater food webs at the regional scale. Our study highlights the value of combining trait-based and network approaches to better anticipate community-level responses to climate change.