Friday, August 6, 2010

PS 107-136: The impact of land management on native bees and plant-pollinator interactions: A case study from Palo Verde, Costa Rica

Zachariah J. Gezon and Rebecca E. Irwin. Dartmouth College


Land-use change is a leading component of global environmental change and can dramatically affect biodiversity and species interactions. While the effects of land-use change on the diversity and abundance of plants is well documented, the effects of land-use change on native insects and plant-insect interactions is less well known. For example, land management changes could alter plant community structure, which may affect diversity of native pollinators and plant-pollinator interactions. The goal of this study was to understand how land-use management affects native pollinator (bee) abundance and subsequent plant-pollinator interactions.

We studied a marsh in Palo Verde National Park, Costa Rica, which is an important wetland for migratory birds. A 300 ha portion of the marsh is managed for cattails, Typha domingensis, using a tractor to crush the cattails thus keeping open habitat for the birds.  The tractor drastically alters the plant community of the marsh by eliminating the wind-pollinated cattail and allowing several species of flowering plants to grow. To determine how the marsh management has affected native bee pollinators and plant-pollinator interactions, we sampled bees using pan traps and netting along 400-m transects, spanning the marsh and adjacent forest, in five managed and five unmanaged areas of the marsh. 


Significantly more bees were caught in the managed marsh than in the unmanaged marsh containing cattail. However, fewer bees were caught in the forest adjacent to the managed marsh than the forest adjacent to the unmanaged marsh. When we compared bee abundance along the transects from the marsh to the forest interior, we caught more bees in the managed marsh than in its adjacent forest, whereas we caught fewer bees in the unmanaged marsh than in its adjacent forest. Finally, we compared the bee abundance across the entire transect area in the managed vs. unmanaged areas and found no difference in total bee abundance. 

These results suggest that management of cattails in the Palo Verde marsh affects bee foraging behavior, likely due to differences in flowering plant abundance or diversity. Flowering plants in the managed marsh likely lure pollinators out of the forest and into the marsh, which could affect the subsequent pollination of forest flowering plants. Taken together, this study shows that management practices that promote growth of flowering plant abundance and diversity may draw native pollinators away from nearby habitats and thus alter the plant-pollinator interactions in managed areas as well as in adjacent areas.