Pollinators in managed ecosystems: Factors influencing diversity

Background/Question/Methods

Pollinators are an important component of ecosystems, with the potential to modify the structure of plant communities because of their influence over plant reproductive success.  More than 90% of flowering plants are animal pollinated, with a majority of those depending on bees for pollination.  The effects of management strategies on bees have been rarely studied, although management strategies can influence the bee community by modifying the distribution, abundance and diversity of nest sites, nesting material and pollen and nectar sources.  Recent efforts to return natural fire-grazing regimes to rangelands have focused on the effects of heterogeneous burning regimes on biodiversity and productivity.  Heterogeneous burning regimes interact with selective foraging by livestock to increase the structure and diversity of plant communities, including the abundance and diversity of forbs.  We evaluated the effect of burn season (spring and summer) and time since burn (year of burn, one year after burn, and two years after burn) on the composition of the bee community at managed rangeland sites in north-central Oklahoma.  We followed a standard protocol for sampling the bee community using pan traps, which have been shown to be an efficient method for sampling bees.

Results/Conclusions

More than forty species of bees were collected during the two year sampling period.  Bee species richness decreased with time since burn and was higher in spring burned plots than summer burned plots.  Bee species richness also varied between years, with more species collected during the dry year (30% less precipitation than normal) when floral resources were scarce than during the wet year (52% more rainfall than normal) when floral resources were abundant.  Similarity in the composition of the bee community increased between spring and summer burned plots with time since burn, and was lowest during the initial year of burn.  The results of this study suggest that heterogeneous burning regimes may support a more diverse bee community than homogeneous burning regimes.  The responses of pollinators to burning regimes have important implications for the conservation of native pollinators and the availability of pollination services at larger spatial scales.  The results of this study provide new insight into how bees respond to management practices and the potential role of managed ecosystems in the conservation of pollinators and maintenance of pollination services.