The structuring of communities through top-down effects of predation by apex predators is well documented. Furthermore, the mesopredator release hypothesis posits that in the absence of apex predators, a mesopredator will be ‘released’, and may take on the suppressive role of a higher order carnivore. However, beyond the exclusion of apex carnivores, this literature largely ignores the effects of an increasingly urban landscape. The few studies that look at the interaction between human influence and the top-down effects of carnivores suggest that humans can exert both top-down and bottom-up pressures that can disrupt natural mechanisms underlying community structure. I tested these findings for broader applicability by comparing temporal activity pattern overlap between the coyote (Canis latrans), a dominant mesocarnivore, and a synanthropic subordinate carnivore, the raccoon (Procyon lotor) across Michigan. The study area consists of the Huron Mountain Club (HMC), Shiawassee National Wildlife Refuge (SNWR), University of Michigan Biological Station (UMBS), and Detroit Metro Parks (DMP), representing distinct zones of human influence from a primary forest at one end to a heavily developed city center at the other. Between October 2015 and March 2018, each site was surveyed for 12 weeks using a camera trap array to determine activity patterns of each species. Our expectation was that the community structuring role of coyotes would be suppressed at both extremes; at the HMC site by an apex predator (Canis lupus), and by anthropogenic influence at the DMP site.
Results/Conclusions
Coyotes and raccoons were detected at every site. Neither the coyote nor the raccoon had significant differences in 24-hour activity patterns across any of the sites. However, raccoons and coyotes had significantly less overlap (p=.027) at UMBS, a site that has an intermediate level of anthropogenic influence. Coyotes exhibited a significant shift in diel period use at the DMP site (p=0.039, 0.002, 0.032, compared to HMC, UMBS, SNWR), using primarily the nocturnal period. Our findings suggest that although anthropogenic pressures cause a shift in the temporal activity of the coyote, there is less temporal partitioning by the subordinate carnivore at both ends of the anthropogenic influence spectrum, consistent with our hypothesis. In an increasingly anthropogenic world, this has important implications for conservation efforts, which need to consider that the underlying mechanisms that structure ecological communities in natural settings may not operate in urban landscapes.