Local and landscape-scale effects on bumble bee occupancy along a rural-urban gradient

Tuesday, November 2, 2021

9:24 AM – 9:36 AM MT

Location: Colorado Convention Center, Meeting Room 103-105

Presenting Author(s)

Claudio Gratton

Professor
University of Wisconsin–Madison
Madison, Wisconsin

Co-Author(s)

LN

Laura Nunes

University of Wisconsin
Madison, Wisconsin
BZ

Benjamin Zuckerberg

Associate Professor
University of Wisconsin
Madison, Wisconsin
TT

Taylor Tai

University of Wisconsin
Madison, Wisconsin

Urban areas often support high bee abundance and diversity, raising the possibility that cities can serve as important conservation refugia for bees. Mechanisms underlying the urban refugia concept center on urban heat island effects, the prevalence of city parks and forests, and the concentration of floral resources. To examine how urban characteristics influence bee distributions, we used standardized repeated surveys of bumble bees (Bombus spp.) centered on Madison, WI, during the summers of 2019 and 2020, and hierarchical occupancy models to estimate detection and occupancy probabilities relative to local (flower abundance and flower diversity) and landscape features (urban to rural gradient) for seven bumble bee species. We found that several bumble bee species were much more likely to occur at sites with higher flower abundance regardless of the surrounding landscape context. The influence of urbanization on bee occupancy was weaker and highly species specific. We identified three general patterns among bumble bees: species with (1) high occupancy in both rural and urban environments (e.g., B. impatiens, B. vagans, B. bimaculatus); 2) low occupancy in both rural and urban environments (B. fervidus, B. auricomus); and 3) high occupancy in only urban environments (B. rufocinctus). Notably, none of the species examined were found to have higher occupancy in rural landscapes relative to urban landscapes. Integration of hierarchical occupancy models will prove useful in estimating unbiased population estimates of insect pollinators, assessing the impacts of urbanization on pollinators and informing pollinator conservation efforts.