Effects of patch size and land cover on body size of bee communities in Denver parks

Abstract

With many bee species at risk of extinction and others suffering population declines, green spaces can be a valuable tool to conserve bees in developed areas. Bees are highly diverse, so species with certain traits might thrive in some parks while others will be more successful in parks with different characteristics. Therefore, research is necessary to examine how various park traits affect the type of bees that can live in them. This study looked at how body size of bee communities in urban parks was affected by park size, proportion of green space, and proportion of natural vegetation. We collected 3193 bees from 25 parks in Denver in summer 2023 and measured intertegular distance in fall 2024 to represent body size. We hypothesized that community weighted mean body size would decrease as park size, green space, and natural vegetation cover increased as larger bees are able to fly farther to obtain food, allowing them to survive in lower quality habitat. Instead, we found no relationship between body size and green space (p=0.64) and only a weak correlation between natural vegetation cover and body size (p=0.27). We also found no relationship between park size and body size when analyzing the full data set (p=0.32). However, when the two largest parks were removed from the analysis, community weighted mean body size increased logarithmically as park size increased (p=0.06). These results suggest that vegetation and land cover have little impact on the size of bees present in urban parks, but park size does have an impact, with smaller bees being more prevalent in smaller parks.