Graduate Thesis Or Dissertation
 

Spatial Ecology and Species Interactions among Predators and their Prey

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/zg64tt39d

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  • Carnivores have disproportionate effects in ecological systems but understanding their exact influences on ecosystems is a matter of great complexity and debate. Predators directly impact prey by killing them, and indirectly by modifying their behavior in response to predation risk. Yet how species interact, both among members of a carnivore guild and between predators and prey, is still a frontier in the field of ecology. Using cougars, coyotes, black bears, and bobcats as model species, I tested methods to estimate carnivore population densities most efficiently, disentangled the intraguild dynamics and species interactions within a terrestrial carnivore community, and studied the spatial response of carnivores to an ephemeral resource pulse of large herbivore neonates. Between 2016 and 2019 I collected data on the four carnivore species at the Starkey Experimental Forest and Range in northeast Oregon. I collected over 1,200 carnivore scats, deployed nearly 100 remote cameras over 3 field seasons, and captured and GPS-collared over 50 individuals encompassing the four study species. I tested a suite of models for density estimation that utilized images of carnivores from remote cameras, individual genotypes determined from scats, capture-recapture data from the effort to capture and collar carnivores, and GPS data from collared individuals. I found that spatial capture-recapture models using genetic data performed the best, but that spatial mark-resight models based on resighting GPS-collared animals using remote cameras were generally in agreement but with lower precision. Methods consisting of photos of unmarked animals from remote cameras performed poorly and generated misleading estimates of population densities for all species. Finally, I developed a novel method to combine data from genetic sources, remote cameras, the physical capture process, and GPS collars into a hybrid model that provided the most precise estimates of animal abundance. I next studied the intraguild interactions between members of the carnivore community. Resource provisioning from competitively-dominant cougars to coyotes through scavenging was so prolific as to be an overwhelming determinant of coyote behavior, space use, and resource acquisition. This was evident via strong attraction of coyotes to cougar kill sites, frequent scavenging of cougar-killed prey, and coyote diets that nearly matched cougars in the magnitude of ungulate consumption. Yet coyotes were often killed by cougars and used space to minimize encounters, complicating the fitness benefits gained from scavenging. I estimated that 23% (95% CI: 8–55%) of the coyote population in our study area was killed by cougars annually suggesting that coyote interactions with cougars are a complex behavioral game of risk and reward. In contrast, I found no indication that bobcat space use or diet was influenced by cougars. Black bears avoided cougars, but there was no evidence of attraction to cougar kill sites, and much lower levels of ungulate consumption and carcass visitation than for coyotes. Finally, I studied the spatial response of the four carnivore species to the seasonal pulse of two large herbivore species using simultaneous GPS locations of the predators and prey. I used step-selection functions to assess whether coyotes, cougars, black bears, and bobcats actively searched for parturient females in a low-density mule deer population and a high-density elk population. I found that none of the four carnivore species encountered parturient mule deer more often than expected by chance suggesting that predation on fawns resulted from incidental encounters. By contrast, I determined that cougar and bear movements positioned them in proximity of parturient elk with male bears driving the observed pattern. In a subsequent analysis, I found that use of parturition habitat dynamically tracked the phenology of the elk birth pulse for bears, but not cougars. These results suggest that of the species studied, only bears shifted habitat use to maximize encounters with elk calves, and in doing so, caused them to encounter elk calves more often than expected by chance. These results contribute to a better understanding of the multitude of effects carnivores have in ecological communities.
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