Agricultural systems have been singled out as systems that expose bees to acute and chronic doses of pesticide mixtures, while limiting forage and increasing dietary stress. While honey bees (and to a lesser extent, other managed bees) are exposed to these stresses, it is reasonable to suspect that these same stressors also impact the diverse assemblage of native bees that could reside in or near farm fields.
In contrast to agricultural systems, urban and suburban gardens have been shown to support surprisingly diverse, abundant and intact bee communities. This is likely because cities often contain exceptionally rich small patches of flowering plants, resulting in high degree of plant species diversity that provide foraging resources for bees. Preliminary findings also suggest that bees’ exposure to pesticides is considerably lower in urban areas compared to agricultural settings. Urban areas may also provide a diversity of nesting substrates that are otherwise rare in agricultural settings. Taken together, these factors help explain observations that urban areas have higher abundance and diversity of bees compared to adjoined agricultural area.
Although it is fairly well-established that urban and suburban gardens host abundant and diverse bee communities, what is less known is whether or not (or the extent to which) urban and suburban garden bees benefit adjacent agricultural systems. At the urban-agriculture interface, it is possible that urban areas could ‘reseed’ agricultural areas with pollinators, each season. However, very little is known about the propensity of urban bees to move beyond garden habitats, and into agricultural systems.
We reviewed the literature to document the diversity of bees that have been identified from urban and suburban garden habitats. We used the literature to consider the potential foraging ranges of common garden bee species, using estimates based on bee body size, as well as experimental observations for select species and their congeners. We apply our findings to hypothetical urban/agricultural landscapes, to identify those urban – agriculture landscape combinations that are most likely to promote bee movement and pollination services into farmland, from urban gardens.
Results/Conclusions
Data suggests that pollination-dependent agriculture systems may benefit from urban bee pollination, if crops are relatively close (e.g. ~0.5 km) to urban gardens. However, landscape elements may impede or promote bee movement across the ecotone. Similarly, resource composition within agricultural and urban landscapes might constrict or expand foraging. We discuss implications for urban ecosystem design.