B.Y.O. Bees: Managing wild bee biodiversity in urban greenspaces

Abstract

As cities become more populated and the density of urban development increases, local biodiversity is threatened. Urban greenspaces have the capacity to preserve pollinator biodiversity, but the quality of support they provide depends on greenspace landscape attributes, including the availability of pollinator habitat and foraging resources. Wild native bees provide important pollination services to urban ecosystems, yet relatively little is known about how urban landscape management influences pollinator community composition and diversity. Our study explores how wild bee communities are affected by greenspace and landscape-level features like pollinator management practices, in urban greenspaces in and around Appleton Wisconsin: a mid-sized urban community spanning more than 100 sq. km. We sampled and identified native bees periodically between late-May 2017 and mid-September of 2018 using standardized arrays of pan traps at 15 sites around the city. We classified greenspaces based on their level of development (urban or suburban) and whether they were managed or unmanaged for increasing wild pollinator diversity. We quantified floral species diversity, floral color diversity, tree species diversity, and proximity of sites to open water for each site and used remotely sensed satellite data from both the USGS National Land Cover Database (NLCD) and the Normalized Difference Vegetation Index (NDVI). All variables were tested as potential correlates of wild bee abundance and species richness. Active pollinator management sites supported higher levels of bee abundance and richness. Notably, active greenspace management (e.g. planting native wildflowers) was a stronger correlate of bee abundance and richness than greenspace size and other landscape-level attributes. Within-greenspace attributes such as floral diversity, tree diversity, and proximity to open water contributed positively to both bee abundance and richness. Based on these findings, we suggest that urban greenspaces may be managed more efficiently and cost-effectively by focusing resources on active management by planting wildflowers, removing invasive species, creating nesting habitat, and providing water resources, rather than simply expanding in area.

Fig 1. Map of urban green spaces categorizing of management status and points representing observed bee species richness.

Blue squares are unmanaged urban sites, green triangles are managed urban sites, red points are managed suburban sites. Basemap generated in ggmap [23] using a Stamen basemap (Map tiles by Stamen Design, under CC BY 3.0. Data by OpenStreetMap, under ODbL).

Fig 2. Bee abundance and species richness across different management practices.

A) Bee abundance across managed suburban, managed urban, and unmanaged urban treatments. B) Bee species richness across managed suburban, managed urban, and unmanaged urban treatments.

Fig 3. Beta diversity and community structure of study sites.

A) Bray-Curtis similarity between sites with two natural clusters identified. B) Test of spatial autocorrelation for richness (grey) and abundance (black). Solid lines and points indicate significant spatial autocorrelation effects. Dashed lines and hollow points indicate non-significant spatial autocorrelation effects. C) NMDS ordination plot of the study sties grouped by the three management types with lines indicating 95% confidence intervals. Solid line indicates suburban managed sites, dotted lines indicate urban managed sites and dashed lines indicate urban unmanaged sites.