Computer Simulation of Furbearer Population Dynamics

FURPOP is a computer simulation model that was developed to simulate the dynamics of raccoon (Procyon lotor) populations in Kentucky. It can be adapted for use with any similar species and location by changing appropriate input data. The program simulates annual population density, age structure, birth rate, and mortality rate based on assumptions concerning the density dependence of factors affecting population change for habitat of specified quality, and based on relationships between harvest pressure and fur market dynamics. Model validity can be tested by using data from a prior year as input, and comparing data from subsequent years with model output. Simulations validly predicted the age structures of raccoon populations in Kentucky (P > 0.05). Management alternatives were explored by comparing output from stochastic runs of the model under “control” conditions with output from simulations in which selected input values had been changed. In experiments with the Kentucky raccoon data set, for example, the long term mean simulated population level was not greatly affected by elimination of hunting and trapping, or the elimination of illegal harvest mortality, but population fluctuations were greater from year to year under these conditions. Reduction in harvest mortality allowed simulated populations to increase more rapidly, and natural mortality subsequently reduced these dense populations to levels below those observed in control simulations. An increase in pelt price stabilized annual fluctuations in population levels observed in control simulations without decreasing the long-term mean density by preventing the population from rapidly growing beyond the capacity of the habitat to support it. When habitat quality inputs were set to extremely high levels, populations increased, but the effects of diseases (i.e., distemper and rabies) prevented populations from approaching the abnormally high carrying capacity. FURPOP was shown to be a valuable tool in assessing the impact of various management strategies on furbearer population dynamics. With further empirical data, the model also can be used to explore assumptions about density-dependent mortality factors, and the impact of habitat quality on population density.