Dispersal pattern and effective population size of the beaver

Abstract

The dispersal pattern of the beaver (Castor canadensis) was studied by intensive livetrapping, tagging, and observation in Allegany State Park and its vicinity in New York from 1984 to 1996. The majority (74%) of dispersing beavers (n = 46) initiated dispersal in a downstream direction after spring ice-out. Females dispersed significantly farther away from their natal colonies than males (10.15 ± 2.42 (SE) km vs. 3.49 ± 0.86 km). Movements to neighboring sites were common (16 of 46 dispersers), indicating that beavers, especially males, may prefer to disperse to the nearest available sites. Most (64%) natal dispersers were 2-year-olds. Three-year-olds also constituted a considerable proportion (21%) of the dispersers, but 1-year-old dispersers were relatively rare (14%). Many adults underwent secondary dispersal after successful natal dispersal in our study area. Male secondary dispersers were more inclined to take over neighboring sites than were male natal dispersers (10 of 13 vs. 3 of 13). The effective population size in a 250-km2 area was estimated to be 161-228 individuals by the areal method and 267-378 individuals by the 85th percentile method.

Post-establishment changes in habitat selection by an invasive species: beavers in the Patagonian steppe

“…This is not surprising as other studies in the native range found juveniles dispersed close to their natal colonies (Sun et al 2000;VanDeelen and Pletscher 1996). The mean distance of a potential new colony to the nearest pond was 864 m, substantially less than the mean distance other studies on beaver dispersal have recorded.…”

“…We followed a used-availability design in which all suitable parts of the landscape are assumed to be available to the individuals but some units are preferred over others. Beavers can travel long distances (we have recorded a 19 km dispersal event in this area using radio-telemetry) (see Leege 1968;Sun et al 2000;VanDeelen and Pletscher 1996), so they are likely to be able to sample all suitable units in the landscape. We decided to take all pixels occupied by watercourses in our study area as the landscape available to beavers.…”

“…At a small scale beavers can expand their home range by impounding new areas nearby, but at a larger scale new ponds can provide insight into the dispersal distances of beavers. A study on beaver dispersal in New York State found that 88 % of the dispersers moved to a location within 5 km from their native colonies (Sun et al 2000). What we do not know is what dispersal distances are in newly invaded regions, and whether those distances change post-establishment.…”

Habitat selection of an expanding beaver (Castor fiber) population in central and upper Morava River basin

“…The colonization process, which corresponds with beaver dispersal and settlement, has mostly been studied at the individual level using telemetry (Beer 1955;Leege 1968;Sun et al 2000;Campbell et al 2005;McNew and Woolf 2005). The data on beaver dispersal, however, were not sufficiently related to habitats.…”

Genetic Population Structure Within and Between Beaver (Castor canadensis) Populations in Illinois

“…Although beavers mate with individuals other than their pair-bonded mate, extrapair mating is not restricted to mating within the colony; rather, numerous occurrences of intercolony extrapair mating have been observed (Crawford et al 2008). Despite reports of nearly equal dispersal rate and distance between the sexes (Bloomquist 2007;Havens 2006;McNew and Woolf 2005;Sun et al 2000), genetic kinship analysis has indicated female philopatry in colonies from 1 of our study populations (Crawford et al 2008). Such sex-biased philopatry can result in high genetic subdivision between breeding groups, because females within colonies will be more closely related to each other than they are to females from other colonies (Storz 1999).…”