UTILITY OF MULTIPLE EQUILIBRIUM CONCEPTS APPLIED TO POPULATION DYNAMICS OF MOOSE

Abstract

Despite the occurrence of several long-term studies, including the celebrated Isle Royale case history, little progress has been made in developing a general theory of natural regulation of moose numbers and much controversy still surrounds the roles of food supply and predation as they relate to moose population dynamics. Recent attempts to formulate such a theory for moose and other northern ungulates include efforts to employ models originally developed by insect and fisheries ecologists. These models include concepts of multiple equilibria in which predation has an increasingly greater impact on recruitment at lower prey densities, thus producing sinuous stock-recruitment curves with stable upper and lower equilibria. When moose numbers are reduced to low levels by hunting or other outside disturbances, the system collapses to very low densities and moose numbers stay in the vicinity of a lower equilibrium unless predators are reduced. These arguments have been used to explain recent moose population declines in Alaska and to suggest remedial management actions. This paper reviews these ideas and concludes that the multiple equilibrium models generated to date may be inappropriate models for moose population dynamics. This results from their failure to capture several important qualitative and quantitative features of moose-predator systems and from the basic inability of stock-recruitment curves to produce realistic moose recruitment functions. Validation of these models has not been possible because existing field data are inadequate.