Predicting the wolf-prey equilibrium point

Difference equation models of wolf and ungulate prey populations were used to estimate the presumed equilibrium ratio by regression of the finite rate of increase of wolf (Canis lupus) populations against wolves per 1000 deer-equivalents of biomass in the prey populations. Further assessment of ratios derived directly from estimates of wolf and prey abundance indicated that such ratios probably substantially overestimate the equilibrium value. This prospect is illustrated by data from Isle Royale. The best present estimate of the equilibrium ratio is 122 deer-equivalents per wolf, a value which indicates that the substantial reductions in moose (Alces alces) populations through predation which has been suggested may be correct. Our results indicate that two-state equilibrium models may not be needed to describe wolf-ungulate equilibria.