Detecting community assembly filters in urban butterflies through analyses of non-Gaussian trait distributions

Abstract

The distributions of ecological traits are commonly used to infer the processes structuring ecological communities, as these processes (deterministic or neutral) select and filter species, leading to distinct trait patterns across communities. Trait distributions are frequently characterised by their average, the community-weighted mean, but increasing evidence exists for non-Gaussian trait distributions in empirical communities. In such situations, community-weighted means are insufficient to capture the patterns of community traits and to infer the implied ecological processes.We analysed the empirical distributions of six functional traits of butterflies from a natural community and a filtered community from an urban area across 6 years.All trait distributions were non-Gaussian, asymmetrical, with relatively long tails (high values of skewness and kurtosis) and multimodal. Results indicate the co-dominance of some trait values, while others rarely occur, and clear differences between the natural and filtered communities; patterns are only adequately described via statistical descriptors beyond community-weighted means. Our analyses allowed us to infer that the filtered community is shaped by a mixture of directional and stabilising assembly filters. The consistent results across the 6 years of data provided further evidence of deterministic processes shaping the assembly of our urban community.Overall, we provide evidence of the ubiquity of non-Gaussian trait distributions across natural and filtered communities, combine multiple statistical descriptors for understanding and comparing such distributions and identify filtering processes structuring these communities.