Effective monitoring techniques for carnivores and the role of a dominant mesocarnivore in structuring the carnivore community

Abstract

Abundance and occupancy estimates are essential to wildlife research, but are often hampered by limited observations, especially for cryptic species like carnivores. Using attractants can increase detections of carnivores, but they must be rigorously tested before use. Similarly, apex predators play a major keystone role in structuring ecosystems but are highly threatened and it is unknown if a dominant mesocarnivore can fill the same role in their absence. I tested the efficacy and decay of two scent lures (sardines and fatty acid tablets) against a control of no lure, to determine if either increased the detections of seven carnivore species; bobcat (Lynx rufus), coyote (Canis latrans), gray fox (Urocyon cinereoargenteus), raccoon (Procyon lotor), striped skunk (Memphitis memphitis), ringtail (Bassariscus astutus), and eastern spotted skunks (Spilogale putorius). I further tested a bait (wild boar carcass) for eastern spotted skunks, a Vulnerable species for who effective monitoring techniques are especially important. I then compared two similar ecosystems, one with pumas (Puma concolor) and one without using spatial and temporal analyses to determine if coyotes, a dominant mesocarnivore, filled the functional role of an apex predator in the absence of pumas, a true apex predator. I found that sardines increased detections of gray foxes, racoons, ringtail, and eastern spotted skunks, but also had a high rate of decay. Fatty acid tablets decayed more slowly but were only effective for gray foxes and raccoons. Wild boar carcass was also highly effective for eastern spotted skunks. In my comparison of ecosystems with and without an apex predator, pumas caused a clear trophic cascade, suppressing coyotes and releasing the smaller mesocarnivores. Conversely, coyotes only suppressed the smaller carnivores by some measures and had overall weaker effects than pumas. My analyses highlight the importance of focal species and study design when using an attractant and the irreplaceability apex predators for structuring the carnivore community.