Re-evaluating the role of density dependence in limiting population growth of moose
Brent R Patterson1,
Alex Bezzina2,
Dani Freund2,
Joe Northrup3
Trent University, Environmental and Life Sciences Graduate Program, Peterborough, Ontario, Canada
Trent University, ENLS
Ontario Ministry of Natural Resources
Abstract Although debate is ongoing regarding how best to model spatial and temporal variation in predation rates, most researchers agree that predation rate is some function of predator abundance, per capita kill rates, and how these interact with prey abundance (i.e. the functional and numerical responses). Both the functional and numerical response may be modulated by a variety of intrinsic and extrinsic factors, but they nonetheless provide the framework for most models of consumer-resource interactions. Moose (Alces alces) abundance can be highly variable over both space and time. Considerable interest remains in trying to explain the proximate and ultimate determinants of population growth rate of moose. This interest is unlikely to diminish anytime soon given recent declines noted for many North American populations. Several researchers have approached this problem using a regression-based framework with population growth rate as the dependent variable and a suite of intrinsic and extrinsic factors as potential explanatory variables. In jurisdictions with wolves, these models typically include some proxy of wolf abundance to account for the potential influence of wolf predation. An interesting, and seemingly paradoxical finding of many of these assessments is that of a strong negative relationship between population growth rate and moose abundance, even at moose abundances well below those at which food competition would be expected to operate. Here, we demonstrate that for regression-based models including only wolf abundance as a proxy, or those failing to consider predation altogether, the finding of strong intrinsic density dependence may be in fact an artefact of a strong functional response by wolves at low to moderate moose abundances. This is an important finding for managers who may mistakenly conclude that actions aimed at increasing carrying capacity for moose will improve population growth rate.