Year of Award

2021

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Fish and Wildlife Biology

Department or School/College

W.A. Franke College of Forestry and Conservation

Committee Chair

Mark Hebblewhite

Commitee Members

Douglas W. Smith, Angela D. Luis, Paul M. Lukacs, Douglas J. Emlen

Keywords

bison, elk, predation, predator-prey, wolves, Yellowstone

Abstract

Predation is a fundamental driver in ecology, structuring ecosystems across the globe. However, understanding the effects of large carnivore predation is limited by both the observation process and the shorter duration of many studies. I used data from 23 years in Yellowstone National Park to disentangle both the importance of wolf predation on prey, and the imperfect observation process of studying predation. I first used field observations to test whether a sexually-selected trait, antlers in male elk, deterred wolf predation. I found that antlers reduced predation risk, emphasizing the selective nature of predation. Next, I used GPS data and ground-based observations to develop wolf sightability models to understand the nature of wolf sightings. I found forest cover, distance from road, topography, and wolf group size affected the probability of observing wolves. Next, I leveraged my sightability model to develop a Bayesian markrecapture abundance model that estimated the number of ungulates fed on by wolf packs during study sessions. I built a model for carcass detection by ground-based observation, aerial-based observation, and GPS cluster searches. Overlooking all details, field methods found only 47% of the estimated occasions when wolf packs fed on ungulates. Using these detection-corrected estimates to evaluate how six wolf predation metrics differed through time as elk declined and stabilized and bison increased, I found that wolf predation on elk generally declined concurrent with the elk decline. I also found that wolf diet (niche) breadth expanded over time primarily by scavenging bison. Though generalizing was challenging, using the simple metric of predation rate, I found predation rate was inversely density dependent in winter on just the wintering elk population within northern Yellowstone National Park. However, wolf predation was conversely a stabilizing force when considering annual predation rate on the entire northern Yellowstone elk population. These observations are consistent with wolves acting as a stabilizing, regulating force on the northern Yellowstone elk population. Finally, I built theoretical models guided by my observations of the wolf-elk-bison system in northern Yellowstone to evaluate how scavenging affects predator-prey dynamics. I found that including scavenging fundamentally changes dynamics, generally increasing prey and predator populations.

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© Copyright 2021 Matthew Caldwell Metz