| Abstract |
Climate change should be shifting species' ranges upslope and poleward as they track their suitable climates. However, many species' ranges are not shifting, with researchers struggling to accurately predict species' sensitivity to climate change. These unexpected responses to climate change could be due to the temporal scale species respond to climate or the role of species' interactions, such as herbivory, in shaping species ranges. My thesis explores how climate and herbivory interact to shape species ranges, providing insights into how these ranges may respond to climate change. First, I test whether the lack of range shifts for many species is because they respond to warming on longer timescales than we measure range shifts. Using a 25-species seed addition experiment, I compared seedling recruitment patterns with adult climatic ranges. I found evidence of a delayed sensitivity to climate change, where range shifts are likely occurring, but responses are delayed and slower than the pace of climate change. Second, I test the assumption that species interactions, like herbivory, are more prevalent towards species' lower range limits and, thus, primarily shape lower over higher limits. While I found herbivory on Lupinus latifolius increases towards warmer temperatures, I also identified herbivore-guild specific precipitation patterns in herbivory. Thus, non-temperature variables can explain unexpected range patterns in species interaction intensity. Finally, I assessed how climate and herbivory jointly influence population dynamics across the range of L. latifolous. Through a field experiment manipulating temperature and herbivory, I found that the strongest effects of herbivory on population dynamics were towards lower elevations. Herbivory effects on populations were driven by a compounding effect of herbivory intensity and climatic stress, which together made plants more vulnerable to herbivory than either factor alone. Overall, my thesis suggests that unexpected species responses to climate change are partly explained by (1) the temporal scale species respond and (2) indirect effects of climate change, where climatic stress makes plants more vulnerable to herbivory. My research advances our knowledge of interacting mechanisms underlying species' population and range dynamics to inform temporal and spatial responses to climate change.
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