Figure 2.

A conceptual model of the hierarchical filtering process which occurs in community assembly, leading to conservatism in the traits defining the β niche and evolutionarily labile traits defining the α niche. Each ball represents a species whose diameter measures a trait such as its SEV for tolerance of soil waterlogging. Only species/balls below a critical diameter can pass through the habitat filter, but then the competitive exclusion filter prevents balls/species that are too similar (shown by their pattern) from coexisting within the same community or quadrat.