Functional Community Assembly is Increasingly Deterministic at Larger Spatial Grain Sizes

Abstract

Community assembly is the result of ecological selection processes, dispersal processes, and random drift processes (Vellend 2010). Selection processes can cause coexisting species to be more similar or more different in traits, depending on the strength of environmental filtering or resource partitioning. Scale in terms of the spatial extent can influence how trait similarity differs from random drift. For example, a grassland could have higher than expected trait diversity by having tall, medium and short species in most samples. But if the scale is expanded to include forests with tall trees, then the grassland plants may have lower than expected trait diversity (Weiher and Keddy 1995). Scale also includes the sample scale or grain size. We sampled the vegetation around coexisting sedges at three grain sizes (0.1 m2, 1 m2, and 10 m2) to investigate if this aspect of scale influences our conclusions about community assembly.