Projecting the impact of climate change on ungulate population dynamics: the importance of trophic interactions

Many projections of climate change impacts on ecological communities do not consider population dynamics or trophic interactions in species responses to climate. Therefore, they do not produce the estimates of population growth needed by wildlife managers. As herbivores, roe deer (Capreolus capreolus) are clearly affected by climate and by interactions with other trophic levels. They are dependent on vegetation for food and subject to predation by multiple species. Consequently, long-term datasets on this ungulate provide the opportunity to explore the importance of trophic interactions while estimating how population dynamics respond to changing climatic conditions. I used the relationship between temporal variation in climate and an index of net primary productivity to project increases in vegetation production for three study sites under future climate scenarios. Analyses of annual variation in the survival and reproductive rates of roe deer at two sites in Sweden demonstrated the importance of indirect effects of climate via changes in vegetation, in addition to the effects of predation and harvest on roe deer demography. Roe deer population growth in response to climate change was estimated using models incorporating both vegetation changes and vital rates into mechanistic simulations. These simulations highlighted the potential for climate change to increase deer population growth and for an increase in harvest and predation to reduce that growth. However, the uncertainty surrounding each level of these analyses was high. Additionally, an investigation of the factors affecting predation of roe deer by the wolf (Canis lupus) identified additional ecological complexities and sources of uncertainty that warrant consideration. This pervasive uncertainty indicates a need for cautious interpretation of results in this thesis, but also provides insight into priorities for future research. Collectively, these analyses demonstrate the theoretical and management value of taking a holistic and demographically explicit approach to estimating species responses to climate change.