Littoral Fish Communities in Lake Tanganyika: Irreplaceable Diversity Supported by Intricate Interactions among Species

The rocky littoral areas of Lake Tanganyika harbor diverse fish communities, mainly composed of cichlids. Their stability, structure, and organizing mechanism were examined at three locations by census, behavioral observations, and dietary analyses. These fish communities were stable, characterized by their persistence during a 10-year period and resilience after a perturbation. Partitioning of spawning sites among substrate spawners was evident, which might be a factor in their ability to coexist. The fish communities were consistently composed of 12 food-habit groups, but composition of species in each group differed from location to location. Among species of different food-habit groups, facultative commensalisms were prevalent. Although aggressive interactions are common among fishes of the same food-habit group, each predatory fish obtained an advantage in feeding efficiency from the different feeding behaviors of other species of the same group. This mutualism and the facultative commensalism should both increase species richness in different parts of the communities. These intricate interactions among species may be a base of stability of the fish communities. We assert that maintenance of ecological networks among species are most important for conservation of biodiversity in tropical regions.