Habitat suitability and source–sink dynamics of beavers

Abstract

Theory suggests that territorial species should share many of the same dynamical characteristics as metapopulations, including asynchronous local dynamics, potential for stochastic extinction of the population when rates of successful dispersal fall below mortality risk, and critical importance of the ratio of suitable to unsuitable habitat for long‐term persistence. These propositions were tested on a population of beavers ( Castor canadensis Kuhl) in Algonquin Provincial Park, Ontario, which has been continuously monitored over 11 years. Results showed that the total population was considerably less variable than local abundance at 14 beaver colonies, due to asynchrony among local populations. This suggests that local ecological interactions were more important in determining year‐to‐year variation in beaver numbers than broad‐scale environmental processes, such as weather. Of the local colonies, 20% were never abandoned over 11 years, although there was considerable turnover among adults. Offspring production exceeded adult abundance at five source colonies, which did not quite compensate for negative net production at nine sink colonies. These observations were consistent with predictions of spatially structured models of territoriality incorporating local variation in habitat suitability. Mean colony size and probability of recurrence from year‐to‐year were associated with local food availability, indicating that trophic interactions were important in determining local population dynamics. The beaver population in Algonquin declined steadily over the study period, however, suggesting that spatial and demographic processes were insufficient to stabilize abundance over time. This is consistent with predictions of spatially structured models of territoriality in which suitable and unsuitable habitats are interspersed. It is hypothesized that long‐term decline in habitat suitability is induced by acceleration of woody plant succession due to selective foraging by beavers.