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.

1. Anthropogenic changes highly impact the world's biodiversity. An important human-driven change to natural environments is increasing urbanisation, which is responsible for decreasing suitable habitats for many wild species, including bees.2. In this study, we investigate if three levels of urbanisation (low, medium and high) affect body size, foraging efforts and abundance of the sweat bee Agapostemon virescens. Overall, A. virescens was more abundant in medium-urbanised sites.3. Second-generation females (summer bees) were more abundant than overwintered (spring bees) at all levels of urbanisation. According to body size, female bees were larger in highly urbanised sites and male bees were larger in medium-urbanised sites. According to foraging efforts, we observed an increase in wing wear during spring and a decrease during summer.4. It was also found a female-biased sex ratio under high urbanisation and a malebiased in low urbanisation sites. Our results suggest that highly urbanised sites can still provide sufficient nesting and foraging resources for A. virescens.5. In addition to our findings of higher bee abundance in low and medium urbanised sites, we suggest that maintaining different levels of urbanisation and heterogenous landscapes within a populous city might have a more positive impact on wild be sustainability.

Elucidating bee response to urbanization is essential to promoting pollinator diversity in cities especially considering such landscapes are projected to expand to support future global populations. To determine how bee community composition and plant–pollinator interactions respond to urbanization, 29 sites representing three urban categories (high, medium and low urbanization) were monitored biweekly from May through early October in Toronto, Canada. Bees were collected passively using pan and blue vane traps as well as actively using aerial nets and vacuums to compare community structure and plant–pollinator networks among urban categories. Functional traits such as dietary breadth, behaviour, nesting substrate and native or non-native status were also examined to determine how landscape influences bee community assemblages. In total, 5477 bees, comprising 26 genera and 164 species, were represented in this study. The urban landscape was largely supportive of species within the family Apidae and Halictidae as well as ground nesting, native and generalist species. Overall, community composition was affected by urban landscape characteristics such as percent tree cover and impervious (i.e. paved and built) surface surrounding sites; however, bee richness and abundance were significantly influenced by plant richness and not by landscape variables. A total of 3267 interactions were observed throughout the study region with characteristics of plant–pollinator networks remaining consistent along the urban gradient with a few floral host plants such as Solidago dominating interactions in certain urban contexts. These results provide important land use and floral host information for targeting pollinator conservation and habitat restoration.