Relative importance of episodic versus chronic mortality in the decline of Vancouver Island marmots (Marmota vancouverensis) [Importance relative de la mortalité épisodique ou chronique dans le déclin de la marmotte de l'île de Vancouver].

Résumé

I used population count data collected from 1979-1998 to evaluate the relative importance of «chronic» versus «episodic» mortality patterns in Vancouver Island marmots (Marmota vancouverensis). I hypothesized that some factors (e.g., gradual vegetation change, forestry effects, or predation) should produce chronic patterns of mortality, and others (disease and weather) should produce episodic patterns. A few colonies had consistently low survival. These results are consistent with a hypothesis of poor quality «sink&» habitats that are maintained by immigration from nearby «sources». However, most colonies had distinct episodes of high mortality, and these appear to be the primary cause of recent population declines. Spatial and temporal patterns of survival are consistent with a hypothesis of disease outbreak or increased hunting effort by predators within a small geographic area. The impact of both factors was probably exacerbated by forestry activities. Results underscore the precarious status of this endangered mammal and illustrate the value of carefully designed annual population surveys.