Phenological Responses of Plants and Pollinators to Human-altered Climates

The timing of plant and animal life cycle events are changing in response to human-altered climates. These shifts in phenological event dates can be detected through time and across space. For example, shifts through time are usually detected in response to global climate alterations, such as increases in average spring temperature since the Industrial Revolution. In contrast, shifts across space are usually detected in response to local-scale climate alterations, such as increases in temperature in urban compared to rural areas. Phenological responses to altered climates can also be studied through experimentation by directly manipulating the relevant environmental cues. Despite the relative ease of phenological measurement, how we interpret phenological shifts and changes to species interactions is not always straightforward. Careful consideration of the metadata, such as the underlying sampling and pooling decisions made across spatial and temporal scales and across levels of biological organization, is often required. In addition to scale-dependency, a lack of knowledge of the cues driving phenological responses further complicates the interpretation of phenological shifts. In my thesis, I address certain knowledge gaps and issues relevant to phenological sampling, scaling, mechanism, and synchrony between interacting species. I do this through the re-analysis of a long-term dataset on plant phenology and through observational and manipulative studies of Cercis canadensis, the eastern redbud tree, and some of its bee pollinators. In Chapter 2, I show how sampling decisions across space and time can affect phenological patterns and our ability to attribute those patterns to climate change. In Chapter 3, I show that the flowering phenology of C. canadensis within the City of Toronto is highly variable in space. This variability correlates with microclimate and may result in greater temporal overlap with certain C. canadensis floral visitors. In Chapter 4, I experimentally manipulate temperature cues and show that cue-response differences can lead to changes in temporal overlap between C. canadensis flowering onset and the emergence of a pollinator, Osmia lignaria. Through the use of novel sampling and experimental approaches, my thesis addresses knowledge gaps in phenological scaling and mechanism and improves our understanding of how plants and pollinators respond to human-altered climates.Ph.D