Limitation and regulation of moose populations: the role of predation

An improved understanding of factors limiting and regulating ungulate populations is vital for sound management, especially with regard to controversial factors like predation. We examine the claim that evidence is weak for predation acting as a major factor limiting or regulating moose (Alces alces) populations in North America. Biologists have been inconsistent in defining limitation and regulation, have used these terms interchangeably, and have incorrectly assumed that major limiting factors regulate moose density. Empirical evidence indicates that many moose populations preyed on by both bears (Ursus arctos and U. americana) and wolves (Canis lupus) persist at densities much lower than K/2 when human influence is minimal. Under these conditions, reduction of predator numbers often results in increased moose density. Reduction of moose from high densities with predators held constant results in inversely density-dependent (anti-regulatory) predation and low moose densities for prolonged periods. In ecosystems lacking bears, or in those subject to substantial human influence, predation may not be a major limiting factor, may vary greatly in its impact, and may be overshadowed by interactions among moose, forage, weather, and hunting that primarily determine moose density. We conclude that in naturally regulated ecosystems, predation on moose by bears and wolves is often limiting and may be regulating, and we identify the conditions necessary for this to occur.