Environmental heterogeneity drives macrophyte beta diversity patterns in permanent and temporary ponds in an agricultural landscape

Understanding patterns of beta diversity (heterogeneity) and its components (substitution and subset) is important for managing freshwater ecosystems and the research on these topics has increased over the last decade. However, there has been limited empirical research exploring the drivers of these components of beta diversity in ponds from agricultural landscapes, in which hydroperiod length is often a key structural driver. The purpose of our work was to examine the contribution of substitution (species replacement among sites without changes in richness) and subset (species differences among sites when species-poor sites constitute subsets of those with a greater number of taxa) structuring processes on macrophyte beta diversity patterns of sixteen permanent and ten temporary Mediterranean ponds. We also aimed to test the structuring role of local environmental factors and geographic isolation and to determine whether there are differences in the community heterogeneity and the relative importance of the substitution and subset fractions of beta diversity between permanent and temporary ponds. We found that temporary ponds were environmentally and biologically less heterogeneous and supported lower richness than permanent waterbodies. In both pond types, beta diversity almost entirely reflected patterns of species substitution rather than subsets. Local environmental conditions, and not among-pond distance, were the main drivers of macrophyte community structure. Overall, our results suggest that local environmental variables operating through niche processes were the primary mechanisms driving macrophyte beta diversity patterns, thus highlighting the importance of environmental heterogeneity for maintaining pond community diversity in agricultural landscapes. Accordingly, conservation initiatives and ecosystem management strategies should include permanent and temporary pond clusters comprising wide environmental gradients in their efforts to ensure high levels of regional biodiversity.