Differences in factors determining taxon-based and trait-based community structures: a field test using zooplankton

Abstract

Ecological community structure, which has traditionally been described in terms of taxonomic units, is driven by dispersal and environmental filters. Traits have recently been recognized as alternative units for quantifying community parameters, but they may have important differences with taxonomic units. For example, as taxon-based community structure is determined by the local species pool, it may be more dispersal-limited, whereas trait-based community structure may be more regulated by environmental conditions because traits are less tied to specific habitat locations. This implies that the relative importance of these two filters may vary depending on the units describing community structure, but no study has yet quantified how the contributions of these filters can differ. In this study, we examined zooplankton assemblages in 87 artificial reservoirs throughout the Japanese archipelago to quantify the relative importance of two filters by examining the effects of spatial configuration (reflecting dispersal filters) and biotic and abiotic variables (reflecting environmental filters) for taxon- and trait-based community structure. Variation in the taxon-based community structure was explained equally well by the spatial and the environmental variables, while variation in the trait-based community structure was explained more by environmental variables. These results support the idea that environmental filters play a more central role in determining trait-based community structures, and show that the relative importance of spatial and environmental filters changes with the way we define community structure.