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 shifts rather than simple species extinction in response to multiple stressors in peri-urban and urban settings. We have investigated the 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, as they had the highest values in bee-site network parameters. Functional diversity increased with urbanization and decreased with pesticide toxicity. Functional redundancy decreased with urbanization. Individual stressors 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.