Phylogeny and the niche structure of meadow plant communities

1 Because related species tend to be ecologically similar, it has long been recognized that the phylogenetic relationships between species in a commun ity are likely to influence its structure. Previous investigations of the i nfluence of phylogeny on community structure have generally shown that cong eneric species are more frequent than would be expected if communities were randomly assembled. Because, under most theories of coexistence, stable co existence requires ecological differences between species, the apparent exc ess of coexisting congeners suggests that trait differences important to co existence must be recently evolved, arising near the tips of phylogenetic t rees. 2 We test this hypothesis in two meadow plant communities for which we have good evidence of niche segregation along axes defined by hydrological cond itions. 3 Niche overlaps were calculated and compared against null models for (i) a ll species in the community, (ii) species within genera, (iii) genera withi n families, (iv) families within the eudicots and monocots, and (v) eudicot s and monocots. 4 Against expectation, we found that community structure was the cumulative result of niche separation arising at a range of phylogenetic levels and t herefore that niche differences have been accumulated through the evolution ary history of species.