EFFECTS OF POPULATION DENSITY AND SELECTIVE HARVEST ON ANTLER PHENOTYPE IN SIMULATED MOOSE POPULATIONS

Abstract

We simulated moose (Alces alces) populations held either at or below carrying capacity (K) to determine the effect of population density on harvest rate and frequency of alleles favoring antler growth under a system of selective harvest. A stochastic model of density-dependent population growth was created to achieve stable populations at K with no hunting. Rates of mortality not associated with hunting were increased to simulate predation last for a population held below K. the increased nutrition available to this lower-density population was assumed to result in larger age-specific antler size. Each population was subjected to a harvest plan that defined legal bulls as those with either a spike-fork antler as yearlings (small bulls) or with an antler spread of > 50 inches (127 cm) as large bulls. Harvest, population composition, and frequency of alleles favorable to antler growth were monitored throughout the simulations. For the population held at K, the frequency of favorable antler alleles declined slightly from that obtained in the population with no hunting. When the population was reduced below K, harvest decreased and their proportion of small bowls in the harvest increased compared with the population at K. In the population below K, the frequency of favorable alleles declined steadily, likely to fixation for unfavorable alleles. Ratio of bulls:100 cows in the two harvested populations were similar but ratios of small:large bulls were changing, with the population at lower density exhibiting a higher proportion of small bulls prior to harvest. Under the conditions imposed by our model, increases in age-specific antler size associated with increased nutrition resulted in greater selection against alleles favorable for antler growth under a scenario of selective harvest. Changes in density of moose populations and resulting effects of nutrition on the potential for antler growth must be considered when predicting the outcome of antler-based selective harvests.