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![]() Changes in the Earth's climate during the past 1.5 million years have had significant impact on the regional and localised distribution of many plants and animals. Nowhere is this more evident than in Sundaland, the term which describes peninsular South-east Asia and large nearby islands. During the various ice ages, vast amounts of water froze at the polar regions, sea levels were low and many land bridges temporarily formed between islands. Shallow parts of the Sunda continental shelf were exposed and temporary land bridges joined present-day Sumatra, Java, Bali and Borneo (comprising Brunei, the Malaysian states of Sabah and Sarawak, and Indonesian Kalimantan) to mainland Asia, allowing a free exchange of animals and plants to occur. When the climate warmed again, the polar ice caps melted, the sea levels rose and these islands were once again separated. This process was repeated many times in the Earth's history. Today, the islands of the Sunda Shelf contain some of the most diverse collections of species found on Earth. This is especially true in wetland habitats, and the rivers and streams of north-eastern Sumatra and south-western Borneo have the highest diversity of any freshwater ecosystems in South-east Asia. Rivers are the arteries of many of these islands, particularly on Borneo where they serve as the main access route to the interior and central highlands. The tortured geological history of the Sunda Shelf has resulted in a pitted, mountainous landscape making these islands a region of great rivers. Among these are the Mahakam (at 920 kilometres, the longest river of the region), Kapuas, Barito and Kayan in Kalimantan, the Rajang and Baram in Sarawak, the Kinabatangan and Padas in Sabah, and the Musi, Batanghari, Indragiri, Kampar and Rokan of Sumatra. Just as rivers take a traveller through all the major habitats of these islands, the rivers themselves reflect a great diversity. Montane streams above 1,000 metres are cold-water torrents which support little vegetation and few wildlife species. Many resident animals, such as insect larvae (caddis flies for example) and fishes (loaches), have flattened bodies and spend much of their time on the river bed, or moving between boulders. Others, such as the sucker fish (Gastromyzon borneensis), have developed suckers to cling to rocks in the fast-flowing current. At lower altitudes, as the water temperature increases and current generally lessens, a wider variety of plants and animals are represented. |