December 25, 2012
Pavement And Low Floral Diversity Drives Away Wild Bumblebees
April Flowers for redOrbit.com - Your Universe Online
Lower numbers of ground-nesting bumblebees, which are important native pollinators, are found in landscapes with larger amounts of paved roads and impervious construction, reveals a new study from The University of Texas at Austin and the University of California, Berkeley.
The researchers also suggest that increasing the number of species-rich flowering patches in suburban and urban gardens, farms, and restored habitats could provide pathways for bees to forage and improve pollination services over larger areas.
Published in a recent issue of Proceedings of the National Academy of Sciences, the findings of this study have major implications for global pollinator conservation on a rapidly urbanizing planet.
"We are potentially in a pollinator crisis," said Shalene Jha, assistant professor of biology at The University of Texas at Austin. "Honey bees are declining precipitously, and wild bees have also been exhibiting population declines across the globe. Native bees provide critical pollination services for fruit, nut, fiber and forage crops. Understanding how bees move around the landscape can help us both preserve biodiversity and improve crop yields."
Jha and his colleague Claire Kremen, professor at UC Berkeley's Department of Environmental Science, Policy and Management, state that animal pollination is estimated to be worth over $200 billion in global crop yields. In habitats across exurban areas, farms and nature reserves, the team studied a native California bumblebee, Bombus vosnesenskii.
The study found that bees will move longer distances to find patches of flowers that are rich in species. Floral diversity, not floral density, is more important in determining how far a bumblebee will fly. The results also revealed that bees will forage further away from their home nest if the surrounding landscape is less heterogeneous.
"In some ways, it's a bet-hedging strategy," said Jha. "If the landscape is composed of consistently dense flowering patches, bees take a risk and forage farther afield to find species-rich patches."
"In combination with earlier work showing that bumblebees have become rare in agricultural landscapes, our study suggests that farmers could promote these valuable pollinators by diversifying crop types and by planting cover crops and flowering hedgerows to enhance floral diversity," said Kremen.
The authors say that our understanding of the effects of pavement and urban growth on native bees has been largely anecdotal, even though it seems obvious that pavement and ground nesting don't mix.
"Using genetic tools, we can now estimate the number of colonies in an area," said Jha, who began this work as a postdoctoral researcher at UC Berkeley. "This is helping us better understand how wild pollinators live and move across large, diverse landscapes."
Each colony of bumblebees nesting in the ground contains a queen and a force of workers. Like honeybees, all worker bumblebees are sisters who spend some of their time flying around searching for flowers from which to collect pollen and nectar to feed the larvae back in the hive. In contrast to honeybees, which are not native, bumblebees do not make harvestable honey. They provide important pollination services for plants, instead.
"Bumblebees are among the most effective native pollinators," said Jha. "They are large and can carry a lot of pollen. They also vibrate or 'buzz' flowers with their bodies and thus are excellent at extracting pollen and moving it from plant to plant."
Instead of scouring the landscape for ground nests, which in the past has proven very difficult over large areas, Jha analyzed the genetic relatedness of bees foraging in the landscape.
Bees collected in the same area that were identified as sisters were from the same colony, while unrelated bees came from a different colony. This information, combined with the bees' locations, was used to estimate the number of bee colonies in an area, as well as determine how far afield the individual bees were foraging.