The importance of riparian wetland habitats for the conservation of biodiversity is well documented for several watersheds. Riparian areas generally have more water available to plants and animals than adjacent uplands. This is of specific importance in regions with a pronounced dry season, where lack of water affects plant growth. Abundance and richness of plant and animal species tend to be greater than in adjacent uplands because they share characteristics with the adjacent upland and aquatic ecosystems and harbor a set of specific riparian species. Because of their richness and their spatial distribution, the relative contribution of riparian ecosystems to total compositional diversity far exceeds the proportion of the landscape they occupy.
Apart from beavers, several other biota act as 'ecological engineers' that create and modify riparian wetlands. African hippopotamus deepen pools and form trails that increase the ponding of the water. Several crocodilians maintain open water channels. Digging mammals, freshwater crabs, and insects like mole crickets increase the pore space in riparian soils and enhance the water exchange between wetland and stream channel. Similar macropores develop from fouling tree roots. Plants also strongly modify the habitat characteristics in riparian wetlands, either actively, by influencing soil, moisture, and light conditions or, passively, by changing the hydraulic conditions through tree fall or organic debris dams.
Typical wetland species are adapted to the amphibious characteristics of the habitats. They are either permanent wetland dwellers that cope with aquatic and dry conditions or they temporarily colonize the wetlands during either the dry or the wet phase. There are many animal species that permanently colonize riparian wetlands, especially anurans, snakes, turtles, racoons, otters, and many smaller mammals, like muskrats, voles, and shrews. Aquatic insects have developed special adaptations to survive periodical droughts, for example, by having short larval periods or drought resistance. Many birds profit by the rich food offered from the aquatic habitats like dippers, kingfishers, jacamars, warblers, and rails. Periodical colonizers from terrestrial ecosystems are bats, elks, moose, and several carnivorous mammals and birds. Many aquatic species like fish and aquatic invertebrates periodically colonize riparian wetlands. Riparian wetland biota belong to the most threatened species as they suffer from both the impacts on the terrestrial and aquatic systems, and many riparian species are threatened with extinction. The effects of extinction of a species are especially high if it is an ecological engineer or a keystone species, for example, a top predator. Extinction of wolves in the Yellowstone National Park in the US led to overbrowsing of broad-leaved riparian trees by increased elk populations.
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