Year of Award

2012

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Wildlife Biology

Department or School/College

College of Forestry and Conservation

Committee Chair

Mark Hebblewhite

Commitee Members

Daniel H. Pletscher, Joel Berger, L. Scott Mills, Marco Musiani

Keywords

population dynamics, predation risk, Rangifer tarandus, resource selection, survival, Woodland caribou

Abstract

Woodland caribou (Rangifer tarandus caribou) have experienced population declines and local extirpations across North America. Human disturbance has caused caribou declines indirectly through changes to apparent competition dynamics within the predator-prey community. Apparent competition occurs as a negative indirect interaction between prey species, mediated by their direct interactions with a shared predator. I first review apparent competition, and show that across many endangered species including woodland caribou, human disturbance often causes an asymmetric tilt to the balance among prey species.

Landscape disturbance such as forest harvest and energy development have created early seral-stage forests and linear features across the landscape of west-central Alberta. I studied the effects of landscape disturbance on the predator-prey dynamics of woodland caribou, wolves (Canis lupus) and other ungulate prey species in this region. I examined spatial patterns of resource selection by caribou, wolf predation risk, adult female caribou survival and, ultimately, population trend for 9 woodland caribou populations. Caribou avoided disturbance across all scales of resource selection, though avoidance of forestry cut-blocks was strongest at broad home range scales and avoidance of linear features was strongest at fine scales along caribou movement paths. Linear disturbances also increased predation risk by being selected as travel routes for hunting wolves, but did not increase the predation efficiency in terms of kills per time, as hypothesized. Rather, spatial changes in predation efficiency were largely driven by natural landscape heterogeneity.

Avoidance by caribou and increased wolf predation risk in disturbed areas indicate functional habitat loss for caribou, yet these patterns alone do not necessarily imply a demographic impact. Spatial analysis of factors influencing adult female survival indicated that caribou resource selection was broadly correlated with survival, but also that wolf predation risk was an additional mortality risk beyond that perceived by caribou. This failure of caribou to non-ideally avoid predation risk may explain my final analysis showing significant and multi-year declines for all populations in west-central Alberta. Ultimately, if caribou conservation is to succeed, management must reverse the ultimate causes shifting the balance of apparent competition at both broad and fine scales across woodland caribou range.

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© Copyright 2012 Nicholas James DeCesare