Date of Award

Spring 2019

Project Type

Thesis

Program or Major

Biological Sciences

Degree Name

Master of Science

First Advisor

Sandra M Rehan

Second Advisor

Donald S Chandler

Third Advisor

James F Haney

Abstract

Globally, wild bees are facing major declines due to many different factors. Land use is regarded as one of the most damaging of these factors as changes in land use can result in the destruction of critical wild bee habitat and foraging resources. Relative abundance and species richness have been used as standard methods for measuring the health of wild bee communities yet neither abundance nor richness are able to quantify how landscape change affects the traits found in members of the population. Phylogenetic methods are a novel tool that can measure community structure by examining how traits influence population structure. The focus of this thesis is to uncover how differences in land use, from grazing to successional states in forests, influence a number of aspects wild bee diversity and community structure.

Landscape change is one of the main drivers of wild bee declines do to alteration in available nesting and foraging resources. This project analyzed the relative abundance, species richness, and the phylogenetic diversity of six landscapes. We found that grazed areas had significantly lower levels of abundance and richness, but it did not alter the phylogenetic diversity of wild bee communities found at grazed sites. Nesting traits were major drivers of the community composition for wild bees found at grazed sites. Landscapes that exhibited lower management intensities and no grazing supported higher bee abundance and richness due to more available nesting substrates and increased foraging densities. Lastly, we found numerous indicator species that can be used for environmental monitoring.

Forest margins offer valuable resources for wild bees in the form of additional nesting substrates and valuable forage, yet only early successional states and mosaic forested landscapes may support diverse bee communities. Our study found that canopy cover, a sign of later successional states in forested landscapes, reduces wild bee abundance and richness. Disturbances within forests were favored by wild bees, as these sites offered warmer climates and more nesting and foraging resources. Additionally, bees were found to distribute themselves close to or further away from forest margins based on their nesting traits.

This research revealed that alterations in landscape has major impacts on the composition of wild bee communities. Certain land use types influence specific functional traits and thus have more influence over how wild bee communities comprise themselves. Grazing was found to be a major negative driving force for wild bees while landscapes that contained a more heterogeneous structure supported a more diverse bee community. This thesis emphasizes the need for heterogeneous landscapes due to their importance in providing much needed foraging and nesting resources for wild bee communities and for wild bee conservation.

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