The relationship of phylogeny to community structure: The cactus yeast community

Species abundances are important properties of ecological communities. Theoretical debate has arisen over whether communities are governed by assembly rules. Some ecologists have suggested that community organization depends on the phylogenetic relatedness of its interacting members. This postulate has not been adequately tested primarily because molecular phylogenies for entire communities are rare. We use the molecular phylogeny and species abundances from the well-studied yeasts that live in decaying cactus tissue (i.e., cactus yeast community) to demonstrate that community structure is indeed linked to genetic relatedness but that the relationship is different for the same yeasts found in hosts of two subfamilies of the Cactaceae. In the Opuntia cacti, the genetically related and unrelated yeasts have equivalent probability of being similar in abundance. Conversely, in the columnar cacti, the abundant yeast species tend to be genetically distant from one another, whereas the rare species tend to be closely related. The distinctive biochemical differences between the Opuntia and columnar cacti habitats suggest that conditions imposed by the environment modify the relationship between phylogenetic relatedness and species abundances in the cactus yeast community.