Photo courtesy of The University of New Mexico's Sevilleta Long-Term Ecological Research Program
Why Monogamy?
The relationship between the male and female is obligate monogamy because the male is needed to ensure the female's reproductive success. Although both the male and female are involved in gathering food and territorial defense, the female could not take on the responsibilities of rearing offspring with out investment from the male. The male is needed to defend the pair’s valuable resources- the dam, and lodge and winter cache. The male is also needed to help gather food and timber for construction and habitat maintenance.
Why a Classical Territory?
Beavers live in a classical territory because of predation pressures
and because of the high amount of investment that goes into establishing
a territory. The beaver dam and lodge (substituted for a bank den in
some situations) requires the work of the entire colony. The dam creates
an aquatic environment that allows the beaver to avoid its terrestrial
predators. Lodge openings that are located underwater also deter predators
from invading the beaver’s home (Jackson 1997). Since beavers invest
so much time into modifying their habitat, they are not able to continually
relocate. For this reason, they must also defend their territory from
non-family beavers looking to establish their own colony.
Predation as a Selection Pressure:
The major selection pressure influencing social spacing and social relationships in the beaver is predation. Since most of the beaver's predators are terrestrial mammals, the beaver is able to avoid predation by building lodges in the middle of artificial ponds. Entrances to these lodges are only underwater, further securing their location. Since it takes so much energy and investment to construct the dams that create their water reservoir, the beaver is tied to its territory. Both the male and female are needed to maintain and defend the territory and raise the young. This is why the beaver lives in a Classical Territory and has an Obligate Monogamous mating system.
Photo Courtesy of North Dakota Game and Fisheries Department
Photo courtesy of Oregon Museum of Science and Industry
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This page was completed in partial fulfillment of the requirements for Biology 323, Animal Behavior, at Davidson College in the Spring Semester 2003.