Bumble bee forager abundance on lowland heaths is predicated by specific floral availability rather than the presence of honey bee foragers: evidence for forage resource partitioning

Abstract

Honey bees are being scrutinized for their potential impact upon wild bees. In lowland heath mosaics, a simple but resource rich habitat for pollinators, there is a higher probability of niche overlap for bumble bees and honey bees due to the requirement of similar resources and limited floral diversity. This study assesses i) if there is any evidence of forage competition between bumble bees and honey bees and ii) asks to what extent the number of bumble bee foragers in a lowland heath mosaic over the summer months is affected by floral resource availability in different heath types (wet/dry). Bumble bee and honey bee counts were conducted at 30 wet heath and 30 dry heath 20 m × 20 m sites, in the Poole Basin, UK. The relationships between bumble bee and honey bee forager observations and ericaceous forage availability throughout the summer were evaluated using GLMMs considering presence and abundance of honey bees and specific floral availability as factors. Only weak correlations of honey bee forager abundance on bumble bee forager abundance were detected. Instead, the most important factors relating to bumble bee numbers were the abundance of specific floral resources within the heath type (wet/dry). Bumble bees and honey bees showed resource use consistent with resource partitioning with bumble bees predominantly using wet heaths and honey bees using dry heaths. These findings provide evidence of the importance of maintaining complex habitat mosaics within broader habitats to promote coexistence between bumble bees and honey bees.