Resource use by an apex mesocarnivore, Pacific marten, in a highly modified forested island ecosystem.
Apex mesocarnivores can have a large influence on the functioning of plant and animal communities. Such effects can be more pronounced in relatively depauperate island ecosystems, especially in the context of a legacy of landscape change and introduced species. One such ecosystem is Haida Gwaii, British Columbia, Canada, where a long history of introduced species and forest harvesting has greatly influenced the composition of the plant and animal communities. Most notably, Sitka black-tailed deer (Odocoileus hemionus sitkensis), an introduced and unchecked invasive species, has interacted with forest harvesting to greatly change the understory structure and composition of those temperate rainforests. Little is known of the habitat ecology of Pacific marten (Martes caurina), the small-bodied apex predator on those islands. We used camera traps to monitor the distribution and habitat ecology of marten across 2 winters. We used mixed-effects logistic regression to test 14 a priori hypotheses represented by statistical models formulated at two spatial scales (100 and 1000 m), with four categories of explanatory factors: sampling bias, forest structure, topography, and human disturbance. Relationships between detections and covariates from the top models revealed that at the 100-m scale, marten were more likely to use habitat that was closer to streams and marine shorelines and that contained a small area of forest harvesting. Marten detections were associated with habitat containing some component of forest edge and road, suggesting foraging behavior adapted to invasive deer, an important source of carrion for marten during winter. The broad use of habitats by Pacific marten suggests that intraguild competition and predation might occur with several species at risk including the endemic Haida ermine (Mustela ermine haidarum). Those two species would likely overlap in diet and distribution when co-occurring across low-elevation coastal habitats. Conservation planning on Haida Gwaii should consider measures that decrease the potential for competition or predation between marten and species at risk.