Principal determinants of aquatic macroinvertebrate communities in small shallow lakes and ponds

Small Shallow Lakes and ponds (SSLs) provide numerous ecosystem services and harbour unique biodiversity. They are very vulnerable to human disturbances and play a central role in ecosystem functioning. In this study, we aimed to disentangle the role of environmental variables in the composition and richness of invertebrate communities using datasets collected from 143 French SSLs with minimal impact from human activities. The SSLs were sampled across four climatic ecoregions, encompassing various geologies and elevations. A hierarchical classification revealed a clear separation into two groups: (1) highland waterbodies and (2) lowland waterbodies. The main environmental variables identified by the db-RDA were elevation associated with climate, and the presence of fish, along with interrelated variables such as SSLs morphology. Generalised additive models GAMs that combined diversity and composition indices or taxonomic richness with determinant environmental variables demonstrated that (1) elevation, mesohabitat complexity and the presence of exotic crayfish strongly influenced the structure, richness, and composition of macroinvertebrate communities, and (2) the presence of fish had a significant impact only on community composition (e.g., reducing the relative richness of typical pond-swimmer taxa). Furthermore, even though connectivity with other waterbodies influenced the macroinvertebrate communities, its impact appeared to be less significant than elevation, climate, and local variables such as the presence of predators (fish or crayfish).