Date of Graduation

12-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Entomology (PhD)

Degree Level

Graduate

Department

Entomology

Advisor/Mentor

Allen Szalanski

Committee Member

Jeffery Barnes

Second Committee Member

Marlis Douglas

Third Committee Member

Donn Johnson

Fourth Committee Member

Kenneth Kvamme

Keywords

Arkansas, Bees, Eastern United States, Ecology, Phylogeography, Pollinator

Abstract

This work addresses multiple knowledge gaps in bee ecology, population health and phylogeography in order to provide insights into the changing distributions of native bees. A comparison of Arkansas bumble bee records mirrors range-wide surveys, with records of stable species (Bombus bimaculatus Cresson, 1863 and B. impatiens Cresson, 1863) increasing three-fold, and records of the declining B. pensylvanicus (DeGeer, 1773) dropping to 60% of historical levels. However, nationally-recommended conservation-genetics tools did not mirror these results on a regional level. Stable and declining species had equivalent genetic diversity in samples from Arkansas and Tennessee (HS range: 0.46-0.63). Diploid males, which indicate inbreeding, were only detected in the species known to be stable, B. bimaculatus and B. impatiens. This could be an indication of broad similarity of these taxa in the region, or it could indicate that recommended microsatellite-based tools are less likely to detect genetic signatures of declines at a localized level.

A three-year survey of floral associations and seasonality in a community of eight bee species across Northwest Arkansas found that local and landscape factors had no effect on the differential abundances of this community, but overall abundance increased with increasing plant richness at each site (F(1,11)=45.62, p<0.001), as did the abundance of each bumble bee species. Bumble bees with long glossae, a group usually thought to be at higher risk of decline, were more specialized in their flower use, and although their food choices overlapped (O12=0.54), they skirted potential competition by maintaining different phenologies.

Subspecies status was maintained for Xylocopa virginica texana Cresson, 1872, but not for X. v. krombeini Hurd, 1961. This morphological east-west differentiation is additionally supported by mitochondrial phylogeographic analyses which suggest that X. virginica expanded from multiple glacial refugia. On the other hand, X. micans haplotypes are consistent with a single origin, likely west of the Mississippi River. In spite of its interpopulation homogeneity, X. micans is quite genetically diverse (Hd=0.91±0.03) compared to X. virginica and (Hd=0.78±0.02), consistent with Hewitt's leading-edge hypothesis for range disparity. Together, these results highlight the importance of an ecological perspective in the quest to understand bee distributions and decline.

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