Habitat complexity predicts the community diversity of rock-dwelling cichlid fish in Lake Malawi, East Africa

Understanding the factors that regulate species diversity remains an important goal in ecology, conservation and evolutionary biology. Speciose communities, like the cichlid fishes in the East African Great Lakes, offer useful opportunities to examine these factors. For example, Lake Malawi supports well over 700 cichlid fish species which likely descended from a common ancestor within the past 2–4 million years. One consequence of this remarkable radiation is the high species diversity of Lake Malawi’s cichlid communities. However, the factors facilitating the assembly and maintenance of species rich cichlid communities have yet to be fully identified. In this study, we examine the diversity of Lake Malawi’s rock-dwelling cichlid communities and investigate the roles that several environmental variables have played in maintaining such high diversity. We surveyed 82 quadrats spanning seven sites and observed 54 species from 12 genera. Most environmental variables that we measured varied significantly within, but did not differ significantly among sampled sites, suggesting that habitat heterogeneity is locally high, but at the lake-wide scale habitats are uniformly heterogeneous. Community diversity was strongly influenced by habitat complexity, while community similarity was strongly dependent on the geographical distance between communities. At the genus level, no relationship between geographic distance and community similarity was found, but community composition was also determined by habitat complexity. Our findings demonstrate that habitat complexity predicts both cichlid species diversity and functional diversity, whereas geographic separation determines the similarities among communities at the species but not at the generic level.