Research in the Holway Lab

Broadly, I study how climate variability and habitat fragmentation interact to shape native bee communities. My work builds on a long-term dataset established by Dr. K. James Hung, who began surveying native bees in San Diego over a decade ago to understand how bee assemblages from fragmented habitat islands differ from  those in large reserves. On the foundation he built, I continue to add to the dataset and expand its scope and the dataset now spans 13 years and has seven complete years of data to investigate landscape scale and species-level traits as drivers of decline. In continued collaboration with James, my explores long-term community shifts, phylogenetic patterns, extinction risk tied to species traits such as range size, and the interaction of variable precipitation and habitat fragmentation.

​Variable winter precipitation interacts with land-use change to affect the diversity and composition of wild bee assemblages

Photos illustrating the difference in the amount of floral resources for bees in a dry year (left - 2022) and a wet year (right - 2024). 
Climate and land-use change rarely act in isolation. In California, rainfall is highly variable, with drought years alternating with years of atmospheric rivers. Using seven survey seasons spanning 2011–2024 (including record droughts and extreme atmospheric river events), we have shown that bee communities respond not only to rainfall in the current year, but also to precipitation from the previous year. Large reserves consistently harbor more diverse and larger-bodied bee assemblages than small habitat fragments, and only reserves show detectable responses to rainfall in both years. These lagged responses suggest that reserves act as reservoirs of species able to persist through unfavorable conditions, while many of these species are already lost from fragments. This work highlights how fragmentation and climate extremes interact to shape pollinator communities in a global biodiversity hotspot.

Check out my poster about this from the 2024 Entomological Society of America meeting.
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Range size as an extinction risk factor

Two species from the same family (Left: Micralictoides ruficaudus, Right: Halictus tripartitus) and their range sizes (center).
Bee photos by Craig Chaddock.
Species with small geographic ranges are widely considered more vulnerable to extinction, but insects are rarely included in such analyses. We use our San Diego bee dataset to test whether range-restricted species are especially at risk in fragmented landscapes. Our findings show that fragments support fewer range-restricted species than reserves, suggesting that range size can help predict vulnerability in insect communities. Because insect ranges remain poorly documented compared to plants and vertebrates, this research underscores the need to integrate museum records and community science data to better understand insect diversity.
Check out my poster on this from the 2024 UC San Diego Biological Sciences retreat.