Demography and ecology of a declining endemic: The Olympic marmot

Abstract

Protected areas serve to conserve species, habitats, and ecological processes. However, biological systems within even large parks are increasingly affected by outside perturbations.

The Olympic marmots (Marmota olympus) are ground-dwelling squirrel that inhabit high-elevation meadows almost exclusively within Olympic National Park Despite this protection, anecdotal reports in the 1990's of disappearances from historically occupied locations suggested that the species was in decline. I used demographic monitoring, habitat surveys, and non-invasive genetic sampling to evaluate population status of the species and consider the effects of several possible stressors.

Olympic marmots disappeared from ∼50% of well-studied colonies, and abandoned burrow complexes were common throughout the park. Estimated annual abundances at intensively studied sites indicated a currently declining population, as did population projections based on measured demographic rates. Low dispersal rates and the spatial distribution of the abandoned sites were inconsistent with metapopulation dynamics as the cause of the declines. There was no evidence that disturbance by tourists was responsible—although marmot behavior differed between remote and regularly-visited sites, there was no corresponding difference in birth or death rates. Likewise, 100% overwinter survival of adults and normal reproductive and juvenile survival rates provide no support for the hypothesis that changes in forage quality or thermal conditions within hibernacula associated with low snowpack were causing the decline. In fact, consecutive year breeding by females during years of early snowmelt suggest a possible positive effect of climate warming. Adult female annual survival was only 0.69, all mortality appeared to be due to predation with coyotes the most common predator, and even moderate changes in adult female mortality rates translated to large changes in projected population growth rates, so it is likely that coyotes are the primary driver of local Olympic marmot declines. Given that marmot populations appear depressed throughout Olympic National Park and that marmots constitute a considerable portion of coyotes diet in many parts of the park (Witczuk 2007), it is likely that this non-native, generalist carnivore is threatening the marmot's existence throughout its range.

As parks become increasingly isolated and surrounded by human perturbations, it will be ever more important to monitor species of special interest within these areas; and when a threat is suspected, to consider more than just the most obvious candidates.