Coexistence of Lake Malawi cichlid fishes

The cichlid fish fauna of Lake Malawi represents one of the fastest examples of large-scale vertebrate evolution on earth. Current estimates suggest that the lake contains over 600 species, all of which have evolved from a common ancestor in under 2 million years. The cichlids have undergone a spectacular adaptive radiation and currently occupy all habitable zones and a variety of trophic niches, but many ecologically closely related coexist side by side within the same assemblages. This thesis contributes to current knowledge of the cichlid faunas by investigating the ecological processes that enable so many species to persist. Niche partitioning is believed by many researchers upon African cichlids to be the primary mechanism maintaining coexistence. Here, I demonstrate that ecological differentiation is commonplace between many sympatrically occurring species, and this is likely to prevent competitive exclusion and generate community structure. However, the role of ecological differentiation is not unequivocal. Many species coexist with large amounts of interspecific ecological overlap. Future work may determine whether alternative processes prevent competitive exclusion amongst these species. Data are further discussed with regard to competition theory, adaptive radiation, and speciation.