Functional diversity across space and time: Trends in wader communities on British estuaries

Aim: British estuarine ecosystems support large populations of protected migratory waders. Understanding how wader communities vary spatially and how they may be changing temporally can greatly improve the understanding of these dynamic ecosystems. Here, we explore the variation in functional diversity (using a range of morphological and ecological traits) in order to identify the processes shaping wader communities on British estuaries and how these processes may be changing. Location: England, Wales and Scotland. Methods: We use national survey data (Wetland Bird Survey) from 1980/1981 to 2006/2007 winter to calculate functional diversity (FD) - an index that measures trait dispersion - in wader communities on 100 estuaries. We test for evidence of non-random patterns of diversity and explore the relative importance of two key processes, environmental filtering and competition, in shaping these communities. Results: The observed FD was significantly and positively associated with species richness and to a lesser extent estuary area, followed by longitude. An increase in observed FD was observed since 1980, supported by a small but significant slope. In the majority of cases, changes in FD were mirrored by changes in species richness. Observed FD was on average lower than expected by chance, as indicated by a negative value of observed minus expected FD. However, this difference became less negative over time, with observed minus expected FD values increasing slightly, but significantly, over the study period. Main conclusions: Wader FD varies across British estuaries, and the relative influence of the processes by which communities are structured appears to be changing through time. We discuss the potential drivers underlying these patterns and the importance of identifying such drivers for the protection of wader communities.