Consequences of intraspecific competition for floral resources in heterogeneous landscapes for eusocial bees

Abstract

Agricultural intensification is widely recognised as a primary driver of pollinator loss, but the success of land-management actions designed to remediate its impact is often mixed. Payments to farmers to increase habitat connectivity or the availability of floral and nesting resources may only result in short-term gains or even unintended consequences. The reasons may lie in changes to interaction networks or competition intensity that remain poorly understood. Models of pollination service typically implicitly assume pollinator population dynamics are regulated by nest-site availability, even though empirical evidence suggests nest-site occupancy is likely at least in part dependent on floral resource availability. To investigate the consequences of competition for floral resources in coarse-grained agricultural landscapes we extended an established model for bees combining optimal foraging and population dynamics, to include new functions for floral resource depletion and realistic colony dynamics. We find that intra-specific competition occurs late in the season forcing bees to forage underutilised sites situated further towards their foraging range limits. A lower rate of energy acquisition ultimately limits the size of the colony peak and delays its timing. Consequently, competition for floral resources can limit population size and distribution while at the same time contributing to a more stable and efficacious pollination service. Although competition was not found to be important in nest-site establishment success, the effect of a hunger gap early in the season on nest-site occupancy indirectly influences competition later in the season leading to complex outcomes.