Beavers were hunted almost to extinction, then bounced back as ecosystem engineers
By felling trees and damming streams, beavers create whole wetlands that many other species depend on, which is why ecologists call them a keystone species. Fur, meat and a scent secretion called castoreum nearly wiped out both living species. Protection since the 19th century let them recover.
Beavers, genus Castor, are big semiaquatic rodents of the Northern Hemisphere and, after capybaras, the second-largest rodents alive, weighing up to 50 kilograms. There are two species, the North American and the Eurasian. The Eurasian one is slightly longer, with a narrower tail, paler fur and triangular rather than square nasal openings. Linnaeus named the Eurasian species, Heinrich Kuhl named the American one in 1820, and many scientists treated them as one species until chromosome evidence in the 1970s settled the matter.
Their engineering is famous. Using branches, mud, rocks and plants, and cutting trees with chisel-like incisors, they build dams that slow water into ponds, with lodges inside for shelter. Pairs are monogamous and live with their young; yearlings help maintain the structures and older siblings may help raise new kits. Territories are marked with scent mounds of mud and castoreum. Their diet is vegetarian: bark, water plants, grasses and sedges.
Their family, Castoridae, has deep roots. It arose in North America in the late Eocene and reached Eurasia over the Bering Land Bridge. About 24 million years ago castorids took up life in water, and extinct relatives included giants such as Castoroides, estimated at around 2 metres long. The genus Castor itself probably began in Eurasia; its earliest fossils, from Germany, are 12 to 10 million years old, and the two living species split around 8 million years ago.
People have prized beavers for pelts, meat and castoreum, used in medicine, perfume and flavouring, and demand for their fur powered much of the fur trade. Both species are now rated least concern. The name comes from Old English beofor, from an Indo-European root meaning brown, and it echoes in European places such as Beverley. The beaver stands for industriousness and is Canada's national animal.
Source: Beaver
