Study of Biotic Homogenization in Bee Communities

Ecology and Evolution graduate student Tina Harrison used a departmental research award in summer of 2011 to explore biotic homogenization in North American wild bee communities. This topic is important because pollinators are critical to ecosystem function and crop production. Biotic homogenization is the process of distinct ecological communities becoming more similar to each other over time due to disturbances such as land use change (i.e. agricultural use and urban/suburban development) and species' invasions. Ecologists are concerned that this process may cause endemic communities to be replaced by assemblages of cosmopolitan, human-associated species.

Tina investigated whether bee communities in disturbed sites were more similar to one another than communities in natural sites. Additionally, she wanted to find out whether this held true across local and regional scales. She used two data sets previously collected by her PhD advisor, Rachael Winfree, from the Pine Barrens in Southern New Jersey and deciduous forests in Northern New Jersey. Using NMDS ordination (a sophisticated statistical approach) she found opposite results at local and regional scales. Within each ecosystem, disturbed sites were actually less similar to one another than were natural sites, indicating that land use change leads to the local biotic differentiation of communities. Across ecosystems, disturbed sites were more similar to one another than were natural sites, indicating that land use change leads to biotic homogenization at regional scales.

One possible explanation for local biotic diversification is that, from the bees' perspective, "disturbed" sites may be comprised of several distinct habitat types. Tina's surprising results illustrate the importance of identifying appropriate biological scales. Tina will continue research on this topic in her first year as a PhD student in the Graduate Program in Ecology & Evolution, and will use these preliminary findings to write proposals for NSF and EPA graduate fellowships.