Neighborhood income, landscape, and local factors relate to differences in pollinator biodiversity in Denver city parks

Abstract

Urbanization is a growing influence on pollinator species worldwide, benefiting some species while threatening others. Urban areas have high cover of impervious surfaces, inconsistent access to floral resources, and competition from non-native honeybees. Urban areas can also be impacted by a "luxury effect", where greater biodiversity is found in more affluent areas. Despite these threats, city parks could be a crucial refuge for pollinator biodiversity. In this study, we investigated how pollinator species richness and community composition differed across Denver city parks depending on landscape-level factors, (neighborhood income and land cover surrounding a park), and local factors, (floral traits and honeybee abundance). After visiting 25 city parks three times during the summer of 2023, we found that income did not strongly relate to wild bee species richness or community composition, but floral species richness and origin did. We found that lower-income parks had a higher proportion of non-native weedy plants and lower wild bee species richness than parks with primarily native plantings. Wild bee communities differed in parks with high compared to low honeybee abundances, with more bumble bees observed in higher honeybee parks. Increased cover of impervious surfaces and income negatively related to butterfly species richness, but butterfly communities remained similar across parks. These findings suggest that managers can implement diverse native plantings in parks to support biodiverse pollinator communities regardless of neighborhood income level.