Urban fragmentation leads to lower floral diversity, with knock-on impacts on bee biodiversity

Abstract

Bees and flowering plants are two closely interacting groups of organisms. Habitat loss and fragmentation associated with urbanisation are major threats to both partners. Yet how and why bee and floral richness and diversity co-vary within the urban landscape remain unclear. Here, we sampled bees and flowering plants in urban green spaces to investigate how bee and flowering plant species richness, their phylogenetic diversity and pollination-relevant functional trait diversity influence each other in response to urban fragmentation. As expected, bee abundance and richness were positively related to flowering plant richness, with bee body size (but not bee richness and diversity) increasing with nectar-holder depth of flowering plants. Causal modelling indicated that bottom-up effects dictated patterns of bee-flower relationships, with urban fragmentation diminishing flowering plants richness and thereby indirectly reducing bee species richness and abundance. The close relationship between bees and flowering plants highlights the risks of their parallel declines in response to land-use change within the urban landscape.

How city traits affect taxonomic and functional diversity of urban wild bee communities: insights from a worldwide analysis

“…In our dataset, highly fragmented green areas seemed to host fewer oligolectic bees probably due to a reduction in the quantity and quality of floral resources (Theodorou et al 2020b). These highly fragmented habitats would probably be insufficient in hosting the specific plant species on which oligolectic species feed.…”

Effect of climate seasonality and vegetation cover on floral resource selection by two stingless bee species

“…Moreover, the effects of changes in seasons linked to the availability of resources have been evidenced in several investigations (Do Nascimento and Nascimento 2012;Samnegård et al 2015;Armas-Quiñonez et al 2020;Theodorou et al 2020), where bottom-up effects (from flowering plants to bees) were highlighted. The behaviour, diversity, and foraging activity of bees are addressed by the flowering seasons, availability, and quality of floral resources.…”

“…Furthermore, the reduction in bee populations in recent years has been attributed to anthropogenic disturbances of natural ecosystems, having strong social, economic, and environmental consequences (Brosi 2009;Brown and Paxton 2009;Powney et al 2019;Potts et al 2010). Forest fragmentation and land use changes have a strong impact on species richness and abundance (Winfree 2010;Xiao et al 2016;Theodorou et al 2020), which deteriorates not only ecosystem structure and function but also species interactions (Valladares et al 2012;Xiao et al 2016;Escobedo-Kenefic et al 2020), and increases the extinction of pollinators as a result of the 50-60% habitat loss, as recorded by Keitt (2009) and Hadley and Betts (2012).…”

Keeping Up with Insect Pollinators in Paris

“…In green spaces, pollinator communities are under the influence of both local and landscape environmental factors [ 6 ]. As demonstrated in Austria [ 7 ] and Germany [ 8 ], local factors seem to be most relevant, foremost among them flower diversity and abundance. Sufficient floral resources are essential to maintaining functionally diverse bee communities, but are impaired by land artificialization.…”