The structure of a thriving community is often dependent on one or two species within the food web. Often referred to as “keystones,” the niche they occupy have broad implications for the other species in the environment. The role of a so-called keystone is often overlooked until it is too late. For example, the regional extirpation of wolves, otters and elephants from their respective ranges led to striking reductions in biodiversity. The loss of just one critical species has unpredictable consequences that include broad ecosystem changes due to a collapsed food web and unintended trophic interactions. In each case, once the keystone is returned to its depleted environment, biodiversity and ecosystem complexity is restored (See Reintroduction of the Wolf).
Because of its destructive tendencies, the beaver (Castor canadensis), is an under appreciated keystone. Known best for felling trees, damming rivers and building lodges, this large semi-aquatic rodent plays a critical role in promoting biodiversity throughout deciduous wetland habitats.
By pruning forests of aspen and ash, beavers create open patches that promote the germinationof herbaceous plants throughout the understory. Rays of sunlight, once blocked by the impenetrable canopy, are now free to initiate the growth of dormant and light hungry species. This seemingly benevolent affair is far from altruistic, beavers drop trees to access tender leaves and repurpose the fallen wood as building materials.
Branches and chiseled tree trunks are carefully piled wherever the sound of flowing water can be heard. By keying into these audible cues, beavers can identify breaches in their fortress and optimize the size of their habitat. The blocked water will flood lowland areas and allow beavers to swim to new forage rather than risk predation by walking clumsily on land.
The dam-building activity not only floods forests, but creates habitat for wood ducks, geese, diving fowl, kingfishers and pileated woodpeckers. The broad habitat modification disrupts climax communities and resets the succession of the forest. As a result, the actions of this one rodent species have a profound impact on the biodiversity structure of forest ecosystems.
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