Date of Award

Summer 8-2022

Document Type


Degree Name

Master of Science (MS)


Biological Sciences



Committee Director

Eric L. Walters

Committee Member

Matthias Leu

Committee Member

Holly Gaff


Islands are not only great models for understanding the ways in which communities are linked by the dispersal of their members to form metacommunities, but are of particular interest to conservationists. One important aspect of metacommunity structure is the degree of nestedness—whether or not less speciose communities are perfect subsets of more speciose communities. Another important metric of metacommunity structure is modularity—the degree to which communities belong to modules composed of other communities that share the same species but have little species overlap with communities from different modules. Environmental gradients have received insufficient attention as predictors of metacommunity nestedness and modularity. I examined bird metacommunities on small islands within the Chesapeake Bay, USA. These islands serve as natural laboratories, representing a gradient of sizes, degrees of isolation, and variation in habitat type. My objective was to determine which, if any, of these variables best predicted patterns of nestedness and modularity. Presence-absence data were collected from thirteen islands in the southern end of Chesapeake Bay from June to August of 2021. Three matrices were developed (ranked by island size, isolation, and habitat type, respectively) and evaluated for both nestedness and modularity. Island size produced the greatest degree of nestedness, even when accounting for variation in species richness across islands.

None of the island characteristics exhibited patterns of modularity. Weighted matrices were developed based on the naturally uneven distributions of islands across these gradients and produced similar results to the non-weighted matrices. These results suggest that, on a broad scale, avian metacommunities across small ((<10,000 ha), nearshore (<10 km) islands will display a nested structure along a gradient of island size, meaning the largest islands contain representatives from most species in the system, and smaller islands are largely redundant in species composition.