Secondary contact during adaptive radiation: a community matrix for Lake Malawi cichlids

We used a community of Lake Malawi rock-dwelling cichlids to study secondary contact during adaptive radiation. Using abundance data from survey plots we constructed a matrix of pair-wise interaction coefficients for males of 21 native and eight transplanted species. After controlling for the effects of habitat variation, correlations among residual male abundances suggest that coevolved species compete less than those brought into artificial secondary contact 30 years ago and that species with the same body colour compete more than those with different body colours. The latter result provides evidence that a trait related to reproductive isolation affects competitive interactions and the distribution of individuals throughout an entire community. Our results further suggest lake level fluctuations that divide and reconnect communities act to increase local (alpha), as well as total (gamma) diversity, in this adaptive radiation. The communities are not, however, unsaturated in the simplest sense; new species can enter a community, but they disproportionately reduce the abundance of original community members.