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Abstract
Phenology, or the timing of biological events, is critical for the development, reproduction, and survival of organisms. One of the most common biological responses to climate change is a shift in phenology. Therefore, an understanding of the drivers underlying changes in phenology is essential in understanding how organisms will respond to a changing environment. This is especially pertinent for organisms that provide critical ecosystem services, such as pollinators. Bees are the most important pollinators in wild and agricultural ecosystems. Solitary nesting bees comprise 90% of total bee diversity, and 65% of total bee diversity nests below ground. Yet, the majority of bee research is focused on above-ground, social species such as the European Honeybee (Apis mellifera) and Bumblebees (Bombus spp.). To better understand how the majority of bees will respond to environmental changes, we need to investigate the drivers and consequences of solitary bee phenology is critical. This dissertation first examines the effect of various dimensions of phenology on solitary-nesting bee reproductive output, and then dives into the environmental correlates of ground-nesting bee phenology. In a subalpine ecosystem, I studied how the timing, duration, and synchrony of nesting activity impact reproductive success for two solitary, above-ground nesting bee species. I found that synchrony is an important predictor of reproductive success for these bees; more synchronous nesting activity increased reproductive success in both species. Additionally, for one species, longer nesting durations increased reproductive output, while the timing of nesting activity had no effect on reproductive success in either species. In this same subalpine ecosystem, I manipulated the soil environment as a proxy for climate change and monitored the emergence phenology of solitary, ground-nesting bees. Here, I found that both soil temperature and soil moisture are important factors in the timing of emergence, but the direction and magnitude of these effects was interactive and varied between years. Finally, I asked a similar question in a coastal dune ecosystem. I manipulated the soil moisture content for solitary, ground-nesting bees and tracked emergence and survival. Because soil moisture and soil temperature are inversely related, my manipulations also altered the soil temperature for these bees. In contrast to the subalpine ground-nesting bees, the coastal dune bee emergence phenology was unresponsive to shifts in the soil environment. Furthermore, the survival of these bees was not affected by soil conditions. Altogether, the results of these studies highlight the complexity of how solitary bees are interacting with their environment. Specifically, I show that the synchrony of phenological activity should be considered when assessing reproductive consequences of phenology. Additionally, phenological responses to the soil environment are context dependent. The drivers of ground-nesting bee phenology depend on interannual variation in the environment and are dependent on the ecosystem at large. My results offer crucial insights into how solitary nesting bees interact with their environment and improve our understanding of how these pollinators will respond to a changing climate.
