Year of Award

2025

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Fish and Wildlife Biology

Department or School/College

Wildlife Biology Program

Committee Chair

Mark Hebblewhite

Commitee Members

Paul Lukacs, Douglas Emlen, Douglas W. Smith, Mahdieh Tourani

Keywords

Canis lupus, Mortality, Reproduction, Survival, Wolf, Yellowstone

Abstract

Populations of animals can be regulated by many factors, including food availability, anthropogenic influences, and social dynamics. Survival of adults and juveniles is one mechanism of population regulation, and these life stages can be influenced by different ecological pressures. In this dissertation, I investigate the ecological, anthropogenic, and social drivers of transboundary gray wolf (Canis lupus) vital rates in and around Yellowstone National Park. First, I evaluate the effect of variable harvest pressure on wolf survival and test whether anthropogenic mortality is compensatory or additive. Theory predicts that under densitydependent conditions, anthropogenic mortality should be offset by a corresponding reduction in natural mortality. I found that overall mortality was highest during years of unlimited harvest, and cause-specific analyses showed that mortality from harvest and conspecifics were the leading causes of death. Harvest mortality was additive, with survival declining in years of increased harvest, while natural mortality remained constant. Next, I test whether adult wolf survival is more strongly influenced by prey availability or social conflict. I compare the effects of elk abundance, relative bison abundance, pack size, wolf abundance, and the presence of older wolves, while controlling for the significant effects found in the first analyses, including harvest pressure. I found that higher elk abundance and larger pack size reduced mortality risk from all causes. Additionally, overall wolf abundance was associated with higher intraspecific mortality. Finally, I investigate how prey availability and social factors affect wolf pup abundance and survival while accounting for imperfect detection. I found that pup abundance increased with pack size and declined during outbreaks of canine distemper virus (CDV) and in certain territories. Pup survival was primarily influenced by CDV outbreaks and territory location, with little evidence for effects of prey availability or social structure. Together, these results demonstrate that gray wolf survival is shaped by a combination of ecological, anthropogenic, and social factors, and that these influences vary by life stage. My findings underscore the importance of considering multiple sources of mortality and variation in ecological context when managing large carnivores, particularly in transboundary systems that include both protected areas and harvested landscapes.

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© Copyright 2025 Brenna Jo Cassidy