Supporting Bees in Cities: How Bees Are Influenced by Local and Landscape Features

Abstract

Urbanization is a major anthropogenic driver of decline for ecologically and economically important taxa including bees. Despite their generally negative impact on pollinators, cities can display a surprising degree of biodiversity compared to other landscapes. The pollinating communities found within these environments, however, tend to be filtered by interacting local and landscape features that comprise the urban matrix. Landscape and local features exert variable influence on pollinators within and across taxa, which ultimately affects community composition in such a way that contributes to functional trait homogenization and reduced phylogenetic diversity. Although previous results are not easily generalizable, bees and pollinators displaying functional trait characteristics such as polylectic diet, cavity-nesting behavior, and later emergence appear most abundant across different examined cities. To preserve particularly vulnerable species, most notably specialists that have become underrepresented within city communities, green spaces like parks and urban gardens have been examined as potential refuges. Such spaces are scattered across the urban matrix and vary in pollinator resource availability. Therefore, ensuring such spaces are optimized for pollinators is imperative. This review examines how urban features affect pollinators in addition to ways these green spaces can be manipulated to promote greater pollinator abundance and diversity.

Keywords: body size; dietary breadth; functional traits; green spaces; habitat fragmentation; microclimate; phylogenetic diversity; pollinator health; urban bees; urban heat island effect.

Figure 1

Diagram displaying some of the interactions between landscape and local features. Arrows represent features affected by other features from which the arrow originates. Local–local (blue), landscape–local (red), and landscape–landscape (yellow) interactions are shown.

Figure 2

Simplistic diagram depicting the filtering of some functional traits comprising urban bee communities. The “net” in the center of the diagram represents a generic urban environment with all its associated local and landscape features that may influence bee community structure. General bee functional traits are presented at the top of the figure whereas traits selectively favored by cities are presented at the bottom.