Lower bumblebee colony reproductive success in agricultural compared with urban environments.

Ash E Samuelson,Ellouise Leadbeater,Richard J Gill,Mark J F Brown

doi:10.1098/rspb.2018.0807

Abstract

Urbanization represents a rapidly growing driver of land-use change. While it is clear that urbanization impacts species abundance and diversity, direct effects of urban land use on animal reproductive success are rarely documented. Here, we show that urban land use is linked to long-term colony reproductive output in a key pollinator. We reared colonies from wild-caught bumblebee (Bombus terrestris) queens, placed them at sites characterized by varying degrees of urbanization from inner city to rural farmland and monitored the production of sexual offspring across the entire colony cycle. Our land-use cluster analysis identified three site categories, and this categorization was a strong predictor of colony performance. Crucially, colonies in the two clusters characterized by urban development produced more sexual offspring than those in the cluster dominated by agricultural land. These colonies also reached higher peak size, had more food stores, encountered fewer parasite invasions and survived for longer. Our results show a link between urbanization and bumblebee colony reproductive success, supporting the theory that urban areas provide a refuge for pollinator populations in an otherwise barren agricultural landscape.

Highlights

We are living in the ‘Urban Age’ [1]: over half the world’s human population currently resides in cities [2] and an estimated threefold increase in global urban land cover is predicted between 2000 and 2030 [3]
Our results demonstrate a direct association between urbanization and higher reproductive output in a key insect pollinator, B. terrestris
We found increases in reproductive output, colony growth and food stores as well as lower brood parasitism by B. vestalis in colonies placed in urbanized areas compared to sites dominated by agriculture

Summary

Introduction

We are living in the ‘Urban Age’ [1]: over half the world’s human population currently resides in cities [2] and an estimated threefold increase in global urban land cover is predicted between 2000 and 2030 [3]. To investigate whether our results may have been driven by floral resource availability, we reanalysed the response variables that were found to be significantly affected by land use (reproductive output, peak colony size, colony survival, queen survival, presence of nectar stores and presence of pollen stores) using the proportion of flower-rich habitat as a predictor.

Results

Conclusion