| Summary: | With climate change, species are shifting their distributions polewards and upwards, and advancing their phenologies. However, there is substantial interspecific variation in these responses and ecologists are having difficulty explaining why. Understanding this variation is critical as it is likely to lead to widespread consequences for trophic interactions and ecological communities. In this thesis, I test several hypotheses concerning the causes and ecological consequences of interspecific and intertaxonomic variation in climate-distribution and phenology-temperature relationships.
First, I tested and found support for the hypothesis that species from different taxonomic groups vary in the strength of climate-distribution relationships, likely because of differences in their life history strategies. However, my results suggest that dispersal ability is unlikely to be the key trait affecting species' geographic distributions at broad scales.
Across broad-scales, I found that butterfly and plant phenologies were strongly affected by temperature, suggesting that phenological shifts in response to future climate change are likely to be widespread. Flight season timing of early-season butterfly species and those with lower dispersal ability was more sensitive to temperature than later-season species and those with greater dispersal ability, suggesting that ecological traits can account for some of the interspecific variation in phenological sensitivity to temperature. Differences in phenological sensitivities of butterflies and plants to temperature imply that shifts in phenological synchrony are likely and could be substantial for interacting species, potentially resulting in important fitness consequences.
Finally, experimentally warming the egg masses and larvae of the western tent caterpillar (Malacosoma californicum pluviale) placed on the branches of its host plant, red alder (Alnus rubra), in the field led to opposing direct and indirect effects on larval development. Warming significantly advanced larval but not leaf emergence, which initially prolonged larval development. However, once leaves were present, warming accelerated larval development, resulting in no overall effects on larval development.
Taken together, this thesis demonstrates that to understand the full implications of climate change for species and communities, accounting for species' life history strategies and interactions will be essential. However, without more quantitative estimates of the fitness consequences of shifts in phenological synchrony, this understanding will be limited.
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