Ecological specialization of Hawaiian Drosophila : II. The community matrix, ecological complementation, and phyletic species packing.

The ecological overlap of three species of Hawaiian Drosophila: D. mimica D. kambysellisi, and D. imparisetae, has been investigated by analysis of the community matrix. The basic model is a Lotka-Volterra formulation, suitably expanded to include sexual dimorphism. We have also investigated equilibrium population sizes and stability properties of all possible communities which might be constructed from these species. Our findings are: 1) There is considerable ecological diversification among these species and between sexes of the same species. 2) The two sexes of any one species overlap more than does either with other components of the community. 3) The two sibling species, D. mimica and D. kambysellisi overlap the least, and D. imparisetae is ecologically intermediate. 4) The current three-species community supports greater numbers than would be maintained by any of the one- or two-species alternatives, and appears to make more efficient use of the available resources. 5) The present community is numerically stable. Although its taxonomic saturation is difficult to judge with certainty, it appears to be unsaturated. 6) The simpler communities would all be invasible by the remaining species. The implications for sympatric speciation of D. mimica and D. kambysellisi are discussed. It is suggested that D. imparisetae might have acted as an ecological wedge, contributing to ecological displacement, reproductive isolation, and further species packing.