Unique Bee Communities within Vacant Lots and Urban Farms Result from Variation in Surrounding Urbanization Intensity

Abstract

We investigated the relative importance of vacant lot and urban farm habitat features and their surrounding landscape context on bee community richness, abundance, composition, and resource use patterns. Three years of pan trap collections from 16 sites yielded a rich assemblage of bees from vacant lots and urban farms, with 98 species documented. We collected a greater bee abundance from vacant lots, and the two forms of greenspace supported significantly different bee communities. Plant-pollinator networks constructed from floral visitation observations revealed that, while the average number of bees utilizing available resources, niche breadth, and niche overlap were similar, the composition of floral resources and common foragers varied by habitat type. Finally, we found that the proportion of impervious surface and number of greenspace patches in the surrounding landscape strongly influenced bee assemblages. At a local scale (100 m radius), patch isolation appeared to limit colonization of vacant lots and urban farms. However, at a larger landscape scale (1000 m radius), increasing urbanization resulted in a greater concentration of bees utilizing vacant lots and urban farms, illustrating that maintaining greenspaces provides important habitat, even within highly developed landscapes.to urban gradients [16,17]. At the same time, landscape features at the city-wide scale can act as strong environmental filters, influencing if taxa from a given species pool are able to colonize distinct greenspace patches [12]. For instance, isolation from other greenspaces can lead to reduced bee species richness within urban forest fragments [18] and connectivity with other greenspaces positively predicts bee abundance on green roofs [19]. In some cases, landscape variables also influence the functional trait distribution found within groups [17,20]. For instance, highly fragmented urban landscapes tend to favor smaller species and cavity nesting species [21,22].At a local scale, species interactions among bees and floral resources can drive patterns of pollinator community assembly [12]. Increasing bee species richness is often linked to floral species richness [23], which frequently increases with the degree of urbanization [4,24,25]. Within a city, urban greenspaces offer a varied breadth and quality of dietary resources [12,[26][27][28][29]. Exotic plant species can make up a substantial portion of the floral resources found in urban areas [30]. Although some exotic species common within vacant lots have been found to be highly attractive [31,32], these resources may also be most suitable for polylectic [33] and/or exotic bees [31]. Urban agroecosystems are likely to have a wider breadth of floral resources, including food crops, native and exotic ornamentals, and many of the same weedy species found in vacant lots. Adding flowering resources, principally native species aimed at supporting pollinators and other beneficial insects, increases available nectar and pollen resources [34] and results in a greater richness and ...

From potential to practical: conserving bees in urban public green spaces

“…For example, weedy species, such as white clover ( Trifolium repens ), red clover ( Trifolium pratense ), and Queen Anne's lace ( Daucus carota ), are the most frequently visited flowering plants in vacant lots in Cleveland, Ohio (Sivakoff et al . ). Furthermore, the seed banks that build within the soils of vacant lots ensure that weedy species will remain important nectar and pollen resources even if those lots are later converted into conservation habitats (Figure ).…”

“…We have documented 98 bee species using weedy plant species as forage, which represents approximately 20% of Ohio's known bee fauna (Sivakoff et al . ).…”

“…; Sivakoff et al . ). Yet, commonly recommended interventions – such as including small patches of bare soil or specifically prepared substrates like pebbles, sand, and heavy clay (Cane ) in pollinator habitats – have not been thoroughly assessed in cities.…”

“…; Sivakoff et al . ), along with non‐native ornamental plants growing in public parks and gardens (Hinners and Hjelmroos‐Koski ). Although non‐native flowers are often considered to be inferior foraging resources (Larson et al .…”

“…; Sivakoff et al . ). Recommendations to maximize the quality of these green spaces for bees often focus on reducing management frequency or intensity, as well as increasing the abundance of flowering vegetation (Garbuzov et al .…”