A Review of Population Dynamics of Furbearers

The term “furbearer” is loosely applied to mammals that are, or have been, harvested primarily for their pelts. Furbearers typically include species ranging from 1–20 kg mass in the orders Marsupialia, Rodentia, and Carnivora. Studies of demography and regulation of populations have important implications to furbearer management and conservation, as well as to population ecology generally. Reproductive potential varies considerably among species, although most species attain sexual maturity within 1 year and have high fertility rates. There is solid evidence for inverse density-dependence in fertility and/or recruitment in muskrats. In longer-lived omnivores and carnivores, variation in reproduction is most often related to changes in pregnancy rates, and/or survival of young. Generalization about density-dependent reproduction among these groups is not warranted from the evidence. For many North American furbearers, the largest fraction of mortality is human-related, primarily from legal harvest, but also vehicle collisions and accidents in some areas. Shorter-lived species respond to increased harvest mortality in a compensatory fashion. However there is evidence that increased harvest may be more additive than compensatory among longer-lived carnivores. Disease may periodically affect annual losses, but evidence that harvest reduces disease outbreaks is equivocal. Dispersal is a prominent behavior among most species and, along with other social behaviors, may influence population regulation. Density-dependent effects in reproduction, mortality, and dispersal often limit effectiveness of controlling population levels of many furbearers. Where lightly-harvested populations are dependent on a single prey species, food supply may regulate carnivore populations — a situation especially apparent in northern landscapes. Simulation has been used effectively to study disease, exploitation, and other aspects of population dynamics. We need a quantitative, theoretical framework to more completely understand how competing sources of mortality interact, particularly the effects of time-lagged responses. Managers need efficient methods to assess population density and rates of change. Population genetics of species of special concern are poorly known and potentially significant to conservation efforts. Although we recognize that habitat heterogeneity and fragmentation influence population dynamics, we are only beginning to quantify the consequences at the metapopulation level. There is need for manipulative, replicated, long-term field experiments to study all aspects of population dynamics.