Ecological factors promoting biodiversity in Lakes BBTM

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Lakes Biwa, Baikal, Tanganyika and Malawi are unique freshwater environments with rich endemic species, respectively. Among these lakes, various kinds of cooperative relationship between species are known from Lake Tanganyika, which might promote to maintain a high biodiversity in a habitat, and such interspecific relationship is plausible in other ancient lakes with a high biodiversity. To ascertain this hypothesis, field observations in Lakes Baikal, Tanganyika and Malawi were conducted.In Lake Tanganyika, more and more various cooperative interspecific relationships among cichlid fishes have been found, especially to avoid the harm from scale-eating fishes and piscivorous fishes. Lake Malawi holds a rich cichlid fauna as well as Lake Tanganyika, and the fish communities of these two lakes are similar in their functional composition. In Lake Malawi, however, the fishes seem to show weak interspecific relationship especially in the views of cooperative foraging and cooperative defense against piscivores and fin-biters.In Lakes Baikal and Biwa, the fish communities are more simple without notable cooperative interspecific relationship. Therefore the biodiversity in fish communities in latter two lakes are, probably, maintained mainly by the interspecific relationship of resource partitioning. In contrast, the biodiversity in fish community in Lake Tanganyika is maintained not only by resource partitioning among species but also by various kinds of cooperative interspecific relationship. The case of Lake Malawi is unclear in this view point, and more detailed survey in Lake Malawi is necessarry to develope the comparative study of biodiversities in ancient lakes.