Density dependence, prey dependence, and population dynamics of martens inOntario

Ecological factors influencing demographic parameters of mammalian carnivor es are poorly understood, due to the difficulty of simultaneously measuring predator and prey populations over an extended period. We used cohort anal ysis based on age-specific harvest data to estimate population densities ov er 20 yr for martens (Martes americana). Marten abundance increased threefo ld over the study period, probably due to relaxation in harvest intensity a t the beginning of the study interval. Changes in rates of population growt h by martens were positively correlated with population densities of three species of small mammals recorded over the same time span: deer mice (Perom yscus maniculatus), red squirrels (Tamiasciuris hudsonicus), and flying squ irrels (Glaucomys sabrinus). We found no evidence of short-term cycles in m arten abundance, nor were there significant cross-correlations at lags grea ter than 1 with prey population densities. Martens also showed evidence of density-dependent population growth. Such density dependence beyond the dem ographic effect of variation in prey density was possibly due to agonistic interactions among territory holders. Such mixtures of prey dependence and density dependence often have a stabilizing influence in theoretical models , which could contribute to the observed stability of deer mouse, red squir rel, and marten populations in Algonquin Park. Harvest intensity was negati vely related to yearly variation in marten population growth. Mortality due to trapping averaged 37.9% over two decades, with no detectable relationsh ip to changes in marten population density. Hence, harvesting acted as a st ochastic external variable that was additive to density-dependent and prey- dependent effects.