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Thesis Abstract – Dolan (2018)

Title:

An evaluation of sampling methodology for surveying bees in California sage scrub fragments

Author and college:

Ellen Dolan, Scripps College

Date:

April 2018

Degree:

Bachelor of Arts in Environment, Economics, & Politics

Advisors:

Diane Thomson, Keck Science Department of Claremont McKenna, Pitzer, and Scripps Colleges
Wallace Meyer, Biology Department, Pomona College

Abstract:

Pollination is a critical ecosystem service threatened by the decline of bee abundances and diversity, yet the question of how native bees respond to habitat loss and fragmentation is understudied. One key gap is a lack of data on the diversity and abundance of bees that remain in fragments of natural habitat. Estimating bee diversity is particularly challenging because collection methods are not well-standardized across studies, and there are few data to evaluate the relative effectiveness of different sampling approaches. Also, bee abundances can vary substantially, both spatially and across years. This study analyzed specimens from three years of bee monitoring with pan traps in fragmented southern California sage scrub. I used these data to quantify how bee capture rates varied spatially across and within CSS patches, and over time. I also compared how trap placement and use of UV or non-UV pans affected capture rates. The average number of bees collected per trap was highly variable year to year. Further, the distributions of bees collected across large, small, edge, and interior habitat patches was inconsistent over the three years. There were no significant differences in collection across large, small, edge, or interior patches for one common pollinator, the non-native European honeybee, Apis mellifera. More bees were captured using pan traps treated with UV paints and in low pan traps on the ground compared to elevated traps. The high spatial and temporal variation in these samples suggests that in order to estimate bee abundances and diversity, surveys must be conducted over several years. I also observed effects of paint type and trap height treatments, suggesting that small differences in methodology can have important effects on capture rates, and likely diversity estimates. Future studies should make a concerted effort to standardize bee collection methodology so that diversity and abundance may be compared more easily across study sites.

For more information:

Contact Diane Thomson – dthomson@kecksci.claremont.edu