Date of Award

January 2016

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

First Advisor

Kathryn A. Yurkonis

Abstract

Plants and arthropods are the base of grassland communities, and their interactions with environmental gradients and each other can determine their composition and spatial structure within a site. The composition and spatial structure of these communities can determine how they contribute to grassland function, yet grassland conservation and restoration efforts typically do not consider both plants and arthropods. As a result, our understanding of how plant and arthropod communities assemble in response to environmental gradients, and each other, in the same space is incomplete. Furthermore, most studies of grassland community assembly do not address assembly across multiple taxonomic levels, and those that do tend to focus on limited groups of taxa. My research expands on this by investigating the response of plants to environmental gradients, and the response of three arthropod functional communities to plant and environmental gradients across a northern tallgrass prairie. Soil abiotic variables and elevation were sampled at 229 plots systematically distributed across UND’s Oakville Prairie in 2014 and 2015. Plant species were surveyed at the same plots in late summer of both years and used to describe plant species composition, native and non-native species composition, non-native species cover, functional group composition, and plant community architecture across the site. Arthropods were sampled in mid- and late summer of both years at three locations in the plant community (litter; mid-story; canopy) in a subset of plots (n = 37). Three environmental gradients (elevation, soil moisture, and soil salinity)

most strongly affected plant community composition in both years. The range of zonation across plant community composition metrics was most similar in response to elevation and most variable in response to soil moisture. Plant community architecture, which strongly affects site use by grassland birds, was not directly associated with site environmental gradients. Results show that plant community zonation patterns can vary depending on the ways in which the plant community is described. Litter arthropods responded to salinity in year one and canopy arthropods responded to salinity in year two. Mid-story arthropods responded to plant gradients in both years, and the salinity gradient in year two. Mid-story arthropods were poorly structured along plant cover gradients that responded to environmental variables, but were well-structured along plant architectural gradients that did not respond to environmental variables. Arthropod functional communities were structured over a wider range of salinity than plant communities. These results show that plants and arthropods can co-vary along strong environmental gradients. These results improve our understanding of how grassland plant and arthropod zonation patterns form in the same space, which can help to inform a more holistic approach to grassland restoration.

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