Date of Award

Spring 5-5-2017

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Ecology and Environmental Sciences

Advisor

Brian J. Olsen

Second Committee Member

Thomas Hodgman

Third Committee Member

Hamish S. Greig

Additional Committee Members

Adrienne I. Kovach

Abstract

Tidal marshes represent one of the most productive natural systems on the globe, but because they are so physiologically stressful, they have low species richness. Consequently, tidal marshes are relatively homogenous across large spatial scales. Within saltmarshes, scale-dependent processes and patterns can be identified with the reduction of variation in community dynamics due to low species turnover. I conducted two studies in tidal marshes along the northeastern U.S. coast to explore the abiotic and biotic factors that influence food-web dynamics and community structure. I explored the effect of temporal and spatial variables on community composition of tidal-marsh invertebrates. I found evidence that invertebrate communities are structured primarily by local- and marsh-level variables whereas regional effects were weak. In addition, my results indicated that invertebrate communities may shift in response to accelerated sea-level rise (SLR), potentially affecting biotic feedbacks that normally allow marshes to keep pace with SLR. Secondly, I tested whether saltmarsh birds exert top-down control on local food-webs. I further explored whether the strength or direction of top-down forces changed across spatial or temporal scales. I conducted avian exclosure experiments in eight tidal marshes along a latitudinal gradient and used a multi-trophic level approach to explore lower-trophic responses to avian exclusion. My results suggest that total invertebrate abundance was most affected by local bird abundance, whereas examining Order-specific responses showed little evidence of spatial variation. Invertebrate response to avian exclusion did not vary across the growing season, but varied year to year. Importantly, plant response was the most consistent across space and time, providing evidence that plant-level measurements may be the best method to reveal the strength and direction of top-down control at large spatial scales. Together, the two studies provide valuable insight into the processes influencing tidal-marsh communities and the scale at which these processes are the most important.

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