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 hab itat where males are known to control access to the algal food resources wi thin their territorial space. These included four sibling species of the Ps eudotropheus (Tropheops) species complex, which are specialized epilithic a lgal herbivores, and two sibling species of the trophically more generalist P. (Maylandia) species complex which feed upon both epilithic algae and pl ankton. 4. The hypotheses that both intraspecific and interspecific territoriality occur in these communities and that interspecific aggression initiated by t erritorial males is preferentially directed at species with the most simila r diets to their own were tested. 5. It was found that males preferred to exclude conspecific intruders, whil e they tolerated intruders with different diets to their own. Also, male P. (Tropheops) preferentially excluded similar heterospecific dietary special ists, while male P. (Maylandia) tolerated similar heterospecific dietary ge neralists. 6. Based on this study, it is proposed that interspecific territoriality ma y be reducing competition between species with different diets and promotin g 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 specializati ons for the same resources may be increasing competition.