Bee ecology and evolution in the context of global change

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Bees are crucial for pollination of many crops and wild plants, yet much remains unknown about the world's ~20,000 wild bee species. The lack of information makes it difficult to know how wild bees will respond to challenges such as climate change and species introductionslet alone make informed management recommendations. My research program will make new discoveries about bees while addressing fundamental questions in insect ecology and evolutionary biology and training students in valuable field, laboratory, and communication skills. In the next five years, we will address three goals: 1. To understand how climate change is affecting solitary bee populations in the southwestern U.S., where drought severity is increasing, we will build on my lab's existing 5-year, multi-site dataset on bee reproduction, flower abundance, and temperature. We will assess how reproductive output of cavity-nesting bees is affected by shifts in the timing of bee emergence relative to flowering time, and by effects of drought on nectar and pollen availability. We will also measure temperatures inside bee nests and test whether warmer temperatures allow bee parasites to accelerate development relative to their hosts. 2. To understand the factors that limit geographic ranges of wild bees, we will study solitary bees in northeastern North America and the Rocky Mountains, asking whether northern or upper-elevation range limits are determined by temperature, abundance of floral host-plants, season length, or the extent of overlap between bee activity periods and flowering. These studies will help us predict how bee ranges will respond to climate change and arrival of non-native plant species with differing flowering times. 3. We will re-evaluate how coevolution between bees and plants has given rise to bee diversity. Bees are normally viewed as beneficial to plants, but as pollen consumers, their relationship with plants is also adversarial. Indeed, pollens of many plant species possess defensive chemicals, suggesting that plants protect their pollen; conversely, certain groups of bees specialize on seemingly defended pollen types, suggesting that they have evolved to overcome the defences. We will conduct field observations of pollen usage by specialist and generalist bee species, syntheses of citizen-science data, and laboratory experiments testing (a) abilities of specialist and generalist bees to use different pollens, and (b) abilities of different pollens to resist infection by fungal pathogens of bees. These studies will provide the first tests of hypotheses for why bees specialize on certain pollen types. The results will help us predict when newly available pollen types will be incorporated in bee diets and make better suggestions about which plants to include in “pollinator-friendly" gardens. Overall, this research will provide novel insights into the evolutionary history of wild bees as well as their future in a rapidly changing world.