Redundancy and Ecosystem Stability in the Fluctuating Environments of Long-Lived Lakes

Abstract

Ancient lakes like Tanganyika and Baikal are hot spots of megadiversity and endemicity. Although extant knowledge on the autecology of the more than 2000 species in each of these lakes is still limited, there seem to be a considerable number of redundant species in these ecosystems. In a more colloquial way, one could say that these lakes have too many species. However, redundancy can be a buffering mechanism against species loss in (more or less predictable) fluctuating environments. Cyclic changes in physical limnology and lake levels at Milankovich time scales have been documented for both Lake Tanganyika and Baikal. Such environmental alterations are bound to affect lacustrine ecosystems. A large number of species per functional guild will allow species loss without ecosystem-collapse. This effect of biodiversity on ecosystem stability presents a paradox, as in times of stasis, selection will favour higher efficiency of energy turn-over within the ecosystem, not mere survival. Competitive exclusion should than reduce diversity. However, post-stress (after extinction) speciation and immigration in ancient lakes increases high diversity levels. These levels of high diversity are maintained during periods of stasis by a combination of niche diversification, with mutualistic species interactions as a special case, and metapopulation dynamics. Conservation programs should thus not focus exclusively on keystone taxa and function, but should rather manage for redundancy as a buffer for ecosystem resilience to both climatic or human induced disturbances. 309