Determining how species coexist in complex environments is critical for understanding functional diversity, niche partitioning and interspecific interactions. Carnivore guild dynamics are interesting to study because members depend on similar foods, overlap in space and time, and can kill each other. Fishers (Pekania pennanti) are members of a diverse mesocarnivore guild and are also of conservation concern in the western United States. Conservation efforts include translocating fishers to reestablish populations and to augment small populations. Only limited research has targeted the effects of translocations on source community dynamics. We studied the effects of translocating approximately 10% of a fisher population on the dynamics of a source mesocarnivore community in a portion of the Klamath-Siskiyou ecoregion of northern California and southern Oregon. We used this translocation of fishers to investigate the effects on fisher population dynamics and tri-trophic interactions among fishers and two other members of the mesocarnivore guild: gray foxes (Urocyon cinereoargenteus) and ringtails (Bassariscus astutus). We use spatial capture-recapture to investigate the effects of this removal on source fisher population dynamics. We used dynamic occupancy modeling that explicitly incorporated interspecific interactions to investigate effects members of these species had on the colonization and survival of each other’s site occupancy.
The population of fishers that we monitored showed no change in density up to 3 years following the removals for reintroduction elsewhere. In contrast, fisher site occupancy significantly decreased in the years immediately following the removals. During this same time period, site occupancy by gray foxes increased significantly and remained elevated through the end of the study. Our occupancy model also indicated that fishers affected gray fox site survival negatively but, interestingly, had a positive effect on colonization of sites by foxes. Fishers also had a negative, indirect effect on ringtail site colonization. Our results are some of the first to elucidate the interspecific interactions among fishers, gray foxes and ringtails. This research also demonstrated discrepancies between density and occupancy estimates for detecting population trends over time. Future studies should investigate the hypothesis that interactions among fishers and gray foxes may also influence the recolonization of fishers to previously occupied habitats in their native range.