Bee community response to multiple stressors along a tropical urban-peri urban gradient

Abstract

Urbanization in tropical landscapes is a complex phenomenon that can lead to community shift rather than simple species extinction in response to multiple stressors in peri-urban and urban settings. We have investigated impacts of different stressors along a tropical urban-peri-urban gradient on the bee community, the health of which is a global conservation concern. Several stressors such as, increased built-up area, pesticide application and air pollution may effectively regulate bee community composition and corresponding functional diversity along urban-peri urban gradients. We investigated the changes in bee community structure in response to associated stressors in 20 locations including parks and gardens along an urban-peri urban gradient surrounding the megacity of Kolkata. Bee community structure differed significantly between urban and peri urban sites with urban sites showing lower value of nestedness. Network analysis also revealed that Apis florea and Lasioglosssum sp. 1 were the most important species in the urban and peri-urban areas respectively. Functional diversity increased with urbanization and decreased with pesticide toxicity. Functional redundancy decreased with urbanization. Individual stressor impacted the bee assemblage differentially along the urbanization gradient. SO₂ and pesticide toxicity negatively influenced bee abundance and diversity. Urban sites sustained more specialized species and therefore are more vulnerable to shocks while peri-urban sites had a more functionally redundant community making it comparatively more resilient.