Georges Etienne Charette, Éric Harvey

There is a growing consensus that cross-ecosystem fluxes significantly influence the structure and stability of aquatic communities. What remains unclear, however, is the relative importance and potential interactions of those fluxes to/with other well-studied factors affecting aquatic community structure such as local environmental parameters or regional-scale influences related to connectivity or habitat size. In this study we compare those different hypotheses by investigating their individual and combined influence on the functional structure of littoral benthic invertebrates’ communities in 7 temperate Canadian lakes (total of 23 sites) located in a semi-protected area. At each site, we sampled macro-invertebrates, we measured C, N, P content of both benthic litter and terrestrial leaves, and we recorded several standard local (pH, dissolved oxygen, turbidity, conductivity, temperature) and regional -scale (perimeter to area ratio, lake connectivity) parameters. We then used a combination of model selection and ordination approaches to disentangle the relative importance of local, regional, and cross-ecosystem factors and their interactions. When considered alone, we found that local factors related to water quality performed best at explaining variations macro-invertebrate community structure. When in combinations, models with both water quality and regional scale variables related to connectivity performed best. However, some functional groups like predator abundances were well correlated to C:N and N:P ratio in sediments (of terrestrial origin). Overall, those results suggest that if stoichiometry (i.e. nutritional quality ) of particulate terrestrial subsidies can have some effects on lake benthic communities, local and regional factors still dominate in explaining invertebrate biodiversity patterns, at least in lakes without steep human land-use gradients. Closing knowledge gaps on cross-ecosystem subsidy effects is important to improve our understanding of how communities and functioning may change under human and/or climate driven changes in watersheds.