Castor canadensis Kuhl, 1820
American beaver
Species recognized by The Integrated Taxonomic Information System
, T Orrell (custodian) in 
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General Description
Description
Source and Additional Information
The largest North American rodent and the only one with a broad, flat, scaly tail, the Beaver is now common and widespread, even in areas it did not inhabit during pre-colonial times. The modifications it makes to the environment by felling trees and building dams result in changes to plant, animal, and microbial communities that are sometimes desirable and sometimes not. The Beaver itself is not easily seen, being nocturnal and secretive, but it can be spotted in ponds, lakes, or large streams at twilight by a quiet observer. Its pelage is brown, with gray underfur, and is prized by trappers. The webbing on its hind feet help it to swim; claws on the digits of its forefeet give it dexterity in handling food; comblike claws on its hind feet help it in careful grooming; and it can close its mouth behind its front teeth, so that it can carry woody material without taking in water. Beavers cache and consume the inner bark of both deciduous and evergreen shrubs and trees, as well as terrestrial and aquatic plants. Their young, called kits, leave the colony at the age of six months.
Adaptation: The shape of the Beaver skull, and the rough texture of its bone, is evidence of a powerful set of chewing muscles. The groove-like depression at the back of the snout and the round one near the jaw joint are areas where large muscles attach. The ridge of bone that marks the curvature below the back angle of the mandible is another muscle attachment site.
Links:
Mammal Species of the World
Click here for The American Society of Mammalogists species account
Adaptation: The shape of the Beaver skull, and the rough texture of its bone, is evidence of a powerful set of chewing muscles. The groove-like depression at the back of the snout and the round one near the jaw joint are areas where large muscles attach. The ridge of bone that marks the curvature below the back angle of the mandible is another muscle attachment site.
Links:
Mammal Species of the World
Click here for The American Society of Mammalogists species account
References
- Kuhl, H., 1820. Beitrage zur zoologie und vergleichenden anatomie, p. 64. Verlag der Hermannschen Buchandlung, Frankfurt am Main, Abt 1. 151 pp.
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Teeth are self-sharpening: American beaver
Source and Additional Information
The teeth of beavers self-sharpen because their inner surface is softer than the outer enamel and wears away faster to create a sharp edge.
"Plant-eaters have to have particularly good teeth. Not only do they use them for very long periods but the material they have to deal with is often very tough. Rats, like other rodents--squirrels, mice, beavers, porcupines--cope with that problem by maintaining open roots to their front gnawing teeth, the incisors, so that they continue to grow throughout the animal's life compensating for wear. They are kept sharp by a simple but very effective self-stropping process. The main body of the rodent incisor is made of dentine, but its front surface is covered by a thick and often brightly coloured layer of enamel which is even harder. The cutting edge of the tooth thus becomes shaped like a chisel. As the top incisors grind over the lower ones the dentine is worn away more quickly and this exposes the blade of enamel at the front keeping a sharp chisel edge." (Attenborough 1979:246)
"Like all rodents, beavers have self-sharpening incisor teeth that never stop growing. The outer surface is protected by tough enamel, but the inner surface is softer and wears away as the beaver gnaws, creating a sharp, chiseled edge." (McKay et al. 2004:222)
Learn more about this functional adaptation.
References
- George McKay; Fred Cooke; Stephen Hutchinson; Richard Vogt; Hugh Dingle. 2004. The Encyclopedia of Animals: A Complete Visual Guide. Berkeley: University of California Press. 608 p.
- Attenborough, D. 1979. Life on earth. Boston, MA: Little, Brown and Company. 319 p.
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Habitat mosaics stop fires: beaver
Source and Additional Information
Beavers reduce fire impacts in spruce stands by creating a mosaic of habitats that act as natural firebreaks.
"Not only do the appetites of moose and beavers help determine when a northern forest will reach this flammable spruce stage, but beavers also indirectly affect the extent of the burn. The mosaic of aspen and willow stands, meadows, ponds, and wetlands they maintain amid the flammable spruce forests can serve as natural firebreaks, keeping fires smaller than they would be in homogeneous landscapes. Both the moose and beaver then benefit from the effects of fire because it clears the way for the regrowth of aspen and willows in the nutrient-laden ash." (Baskin 1997: 168)
Learn more about this functional adaptation.
References
- Baskin, Y. 1997. The Work of Nature: How The Diversity Of Life Sustains Us. Island Press.
Enhancing species richness: beavers
Source and Additional Information
Beavers enhance species richness in their environments by increasing habitat heterogeneity.
"Many organisms modulate the availability of resources to other species by causing state changes in biotic or abiotic materials (ecosystem engineering), in the process frequently changing the selection to which the ecosystem engineers and other organisms are exposed (niche construction)…Jones and colleagues (1997) hypothesized that at a scale encompassing unmodified or 'virgin' habitats, engineered habitats, and degraded areas abandoned by engineers, the net effect of ecosystem engineering should be to enhance species richness via a net increase in habitat diversity. Recent studies provide support for this hypothesis. For example, natural sites with and without beavers (Castor canadensis) exhibit low overlap in species composition. By increasing habitat heterogeneity, beavers increased herbaceous plant species numbers by more than 33% (Wright et al. 2002)." (Boogert 2006:570, 574)
Learn more about this functional adaptation.
References
- Boogert, Neeltje J.; Paterson, David M.; Laland, Kevin N. 2006. The Implications of Niche Construction and Ecosystem Engineering for Conservation Biology. BioScience. 56(7): 570-578.
- Jones CG; Lawton JH; Shachak M. 1997. Positive and negative effects of organisms as physical ecosystem engineers. Ecology. 78: 1946-1957.
- Wright JP; Jones CG; Flecker AS. 2002. An ecosystem engineer, the beaver, increases species richness at the landscape scale. Oecologia. 132: 96-101.
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Last curated:
04 Dec 2009
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Paddy Patterson.
Editor.
"Castor canadensis Kuhl, 1820". Encyclopedia of Life, available from "http://www.eol.org/pages/328025". Accessed
21 Mar 2010.
