Endemism in Aquatic Ecosystems

Abstract

Endemic species are unique to a certain water body, place or region. Neoendemics live in the cradle in which they originated; paleoendemics used to have wider distributions in the past, but occur in relict populations in a more restricted area now. Most endemics occur in water bodies that are both large and old, such as the ancient lakes of Baikal and Tanganyika, but these two conditions are by themselves not sufficient to explain high levels of endemicity. Apart from other ancient lakes, large and ancient river basins such as the Amazon River, harbor many endemics. The same is true for certain hypersaline lakes (Australia) and even temporary pools (South West Africa) in xeric areas and in groundwater. Some taxonomic groups are more prone to forming species and endemic species flocks than others. The fish family Cichlidae has hundreds of endemic species in the three African lakes Victoria, Tanganyika and Malawi, numbers which are unmatched by the dozens of other fish families that also have representatives in these lakes. Particular biological traits seem to make certain groups more prone to high speciation rates and to being endemic. Several traits that impede dispersal, such as absence of dispersal stages and philopatry, appear to be important. The interaction of such intrinsic traits, with extrinsic events, such as climate driven lake level fluctuations, can lead to increased speciation and high levels of endemicity. Habitat degradation and destruction as well as invading alien species in hot spots of endemism are the most important threats for endemics, which are mostly highly adapted to their specific environment. Such threats are often human induced.