Freshwater and Key Watersheds,
Biodiversity Centers, Sumatra and Associated Islands

Major lakes occur in every province in Sumatra. Because these lakes have been isolated for long periods of time they have extremely different fauna and flora. However, past palaeo connections between the rivers of eastern Sumatra and western peninsular Malaysia insinuate closer faunal relationships between some elements of the freshwater fauna of these areas than occurs between rivers in eastern Sumatra and those elsewhere in Sumatra.
For example, the same species of Freshwater Stingray (Dasyatis sp) occur in both the Indragiri River, East Sumatra, and the Perak River, western Malaysia (Taniuchi (1979).
Seven of the 15 Sumatran lakes listed in the above table have been studied. In none of these were there sharp temperature gradients -- the maximum difference between top and bottom did not exceed 5.5 degrees centigrade. The euphotic zone was generally the same as the epilimnion, and the lakes were stratified with relative little overturn of water strata (Ruttner 1931). Some of the deeper lakes, such as Lake Kawar, have few biota whereas the shallower higher nutrient lakes have a rich invertebrate fauna and probably also fish fauna (Whitten et al. 1997).

The oriental family Irenidae, comprising the fairy blue wren birds (Irena), leafbirds (Chloropsis) and ioras (Aegithina), appear to have their center of evolution in Sumatra (Dunn 1974).
The Tesso Nilo forest in Riau Province consists of 188,000 ha and is one of the remaining extensive areas of Lowland Rainforest in Sumatra. This forest has one of the highest known diversities of vascular plant species in the world. It is also one of the few remaining safe havens for elephants in Sumatra (WWF Indonesia 2003).
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