Coexistence induced by pollen limitation in flowering-plant species.

We report a novel mechanism for species coexistence that does not invoke a trade-off relationship in the case of outbreeding flowering plants. Competition for pollination services may lead to interspecific segregation of the timing of flowering among plants. This, in turn, sets limits on the pollination services, which restrain the population growth of a competitively superior species, thereby allowing an inferior species to sustain its population in the habitat. This explains the often-observed tendency for interspecific differentiation in the timing of flowering between coexisting plants. It also predicts that the introduction of an efficient pollinator to a habitat may cause the extinction of competitively inferior plant species.