SIMILARITY AND LOCAL COEXISTENCE OF SPECIES IN REGIONAL BIOTAS

The notion of `community-wide character displacement' hypothesizes tha t locally co-existing sets of competing species should be less similar than expected when compared to random expectations from a broader reg ional species pool. Here I use a mechanistic approach to the niche con cept to show how this expectation is dependent on the types of traits involved. I investigate how two different niche components, those that relate to species' requirements (or responses to environmental factor s) versus those that relate to species' impacts (or effects on environ mental factors), a?ect predictions about the similarity of locally co- existing species. In contrast with more conventional approaches that f ocus on species impacts, I focus on species responses to conclude that locally co-existing species should be more similar in such traits tha n expected on the basis of random assortment from a larger equilibrium regional biota. In addition, I explore the evolutionary implications of exceptions that might favour the co-existence of species with dissi milar traits (especially those that determine species' impacts on the environment) and conclude that these implications di?er when species c ompete for shared resources, interact via shared predators, or interac t via both mechanisms. The analysis developed in this paper shows that the co-existence of species that are more similar than expected by ch ance is not incompatible with the notion of strongly interacting speci es in saturated local communities near equilibrium.