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Contributed Poster

Session: Pollination

PS 17-246 - Making bee-friendly yards: Occupancy models of urban bees

Monday, August 7, 2023
5:00 PM – 6:30 PM PDT
Location: ESA Exhibit Hall
Abstract: Native bee populations need to be conserved to maintain healthy pollination networks with native plants and all other organisms that rely on them. As human pressures affecting bee populations increase, conservating bee diversity within human-dominated landscapes is vital. In this study, we collaborated with volunteers through the Shutterbee Citizen Science Program to photo-document bee diversity in residential and community gardens in the St. Louis region in Missouri and Illinois. Citizen scientists conducted biweekly photo surveys of foraging bees between June and September of 2020 and 2021, and the bees and plants were then identified by the research team to the lowest taxonomic level possible. We estimated percent impervious surface and housing density within a 500m radius surrounding each garden and estimated flower density, flower cover area, and habitat complexity within each garden. We then explored the impact of landscape and local factors on the populations of two native, distantly related tribes of bees: Augochlorini (genera Augochlorella, Augochloropsis, and Augochlora) and Osmiini (genera Heriades and Hoplitis). We analyzed the response of each tribe to our predictor variables using Bayesian occupancy-detection modeling. Detection parameters included day of year, observer, and total search time. Occupancy parameters included impervious surface, housing density, flower density, and habitat complexity. In support of our hypothesis, Augochlorini (which contain both ground- and stem-nesting species) were primarily negatively affected by urbanization, whereas Osmiini (which are stem nesters) were positively affected by urbanization. Specifically, occupancy probability of Augochlorini decreased with percent impervious surface cover and housing unit density. Osmiini, on the other hand, exhibited increased occupancy with increased impervious surface and housing unit density. Interestingly, Osmiini exhibited decreasing occupancy with increasing flower density, whereas Augochlorini were positively affected. We had predicted that both species would be positively influenced by flower density. Occupancy of Osmiini increased with habitat complexity, but Augochlorini was insensitive to changes in habitat complexity. Our results suggest that Osmiini may benefit from increased stem density available in more complex habitats, whereas Aughochlorini is negatively impacted. Future research will explore the role of floral and nesting resource availability on occupancy of these and other taxa in order to test this prediction. Similar to results shown elsewhere, the results of this study indicate that urbanization can negatively or positively affect native bee populations under specific conditions, suggesting that more nuanced recommendations for bee conservation are warranted.