Space use and temporal relationships among western spotted skunks (Spilogale gracilis) and two competing mesocarnivores on the Olympic Peninsula of Washington

Abstract

Among sympatric carnivores, acts of interference competition range in intensity from the threat of attack to interspecific killing (IK). If IK is a regular outcome of encounters between two carnivores, the subordinate species may be forced to avoid the other in space and/or time. Carnivores are at the greatest risk of becoming victims of IK if they are 2–4 times smaller than their potential attacker. Thus, the spatial distributions and activity patterns of small carnivores may be dictated by the presence of larger competitors. However, many species rely on constitutive defenses—those that are always present and provide continuous protection—to reduce the risk of mortality during encounters with predators, and thus small, but constitutively defended, carnivores such as skunks may not respond to the threat of IK through spatial or temporal avoidance. To explore the hypothesis that the risk of predation and IK by larger competitors is mitigated by constitutive defenses, we used multispecies occupancy models and detection/non-detection data from baited camera stations and collocated hair snares to test for pairwise interaction effects on the space use of western spotted skunks (Spilogale gracilis), coyotes (Canis latrans), and bobcats (Felis rufus) on the Olympic Peninsula of Washington, USA. Use of a multispecies occupancy model simultaneously allowed us to examine the spatial relationship between coyotes and bobcats and thus we also tested a secondary hypothesis that the slight body size disparity between the coyotes and bobcats and high dietary overlap between the two species promotes IK, which is dominated by coyotes. We also used timestamp data taken from camera detections to analyze the temporal overlap of daily activity patterns of all three species. We found no evidence of spatial or temporal avoidance among the three focal species. Our best supported occupancy model indicated that these species use space independently of one another, and we found high levels of temporal overlap among all three species. Our findings suggest that neither western spotted skunks nor bobcats fall victim to IK at a great enough rate to promote avoidance of their respective potential attacker(s). The decision to engage in IK is influenced by many risk and reward factors and the constitutive defense of western spotted skunks is likely a strong deterrent. Likewise, bobcats may be too formidable of an opponent— armed with sharp claws in addition to teeth—for coyotes to attack with regularity.