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theses

Human land use has variable effects on ecological communities at local and landscape scales, but these effects cumulate in clear trends of species loss and decline at larger continental scales. Linking changes in biodiversity across scales is therefore a major research challenge for global change ecologists. In a worst-case scenario known as biotic homogenization, anthropogenic changes such as land use drive the replacement of sensitive endemic species by widespread, disturbance-adapted species, leading to potentially little change in species diversity at small scales, but driving loss of diversity at larger scales as historically distinct communities become compositionally similar. This dissertation explores the role of land use in driving biotic homogenization and other forms of biodiversity change across spatial scales, using bee pollinators collected from a large-scale study design including forest, agriculture, and urban landscapes replicated across four distinct vegetation zones of the northeastern U.S. I used this dataset to ask (1) Do anthropogenic landscapes alter alpha diversity and composition of bee communities, and (2) Are anthropogenic landscapes homogenizing bee communities across regional spatial scales? I used a literature review focused specifically on the role of urban land use, to ask (3) how do urban drivers affect the interactions between plants and pollinators, including bees? Relative to natural forest habitat, bee communities in agriculture and urban landscapes were less diverse, had fewer rare species, and were dominated by species with long flight seasons and social behavior. These changes in species composition did not result in detectable homogenization of species composition across anthropogenic versus natural landscapes. However, bee communities in anthropogenic landscapes were more closely related to one another, both within and across sites, indicating that land use is associated with a loss of phylogenetic diversity at small and large spatial scales. The literature review identified habitat fragmentation, invasive species, urban warming, and pollution as key drivers of change in bee communities and plant-pollinator interactions in urban landscapes. Overall, negative effects of land use on bee biodiversity were subtle and often masked by more dramatic changes bee community composition. This indicates both current resiliency and a potential for large-scale biodiversity loss and decline in the context of continued land use change.

ETD_7605

Ph.D.

Includes bibliographical references

by Tina Harrison

doi:10.7282/T3BV7JX6

ETD doctoral

The author owns the copyright to this work.