Resource control by territorial male cichlid fish in Lake Malawi

1, The rocky habitat communities of Lake Malawi contain a high diversity of ecologically similar, predominantly herbivorous, cichlid fish species. How so many species can coexist is still unknown. 2, Adult males of the majority of these species hold permanent territories which form dense multispecies mosaics across the shores. 3. The study examined six coexisting species of cichlids from the rocky habitat where males are known to control access to the algal food resources within their territorial space. These included four sibling species of the Pseudotropheus (Tropheops) species complex, which are specialized epilithic algal herbivores, and two sibling species of the trophically more generalist P. (Maylandia) species complex which feed upon both epilithic algae and plankton. 4. The hypotheses that both intraspecific and interspecific territoriality occur in these communities and that interspecific aggression initiated by territorial males is preferentially directed at species with the most similar diets to their own were tested. 5. It was found that males preferred to exclude conspecific intruders, while they tolerated intruders with different diets to their own. Also, male P. (Tropheops) preferentially excluded similar heterospecific dietary specialists, while male P. (Maylandia) tolerated similar heterospecific dietary generalists. 6. Based on this study, it is proposed that interspecific territoriality may be reducing competition between species with different diets and promoting their coexistence, while it may be enhancing competition between species with the same diet. Furthermore, it suggests that ecological generalism may be reducing the intensity of interspecific competition, while specializations for the same resources may be increasing competition.