Influence of Landscape Heterogeneity on Local and Regional Biodiversity and Species Composition in Natural and Experimental Metacommunities
Mausbach, William Eugene
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Environmental heterogeneity is often studied using differences in resource availability; however, heterogeneity can be represented in a variety of patterns across many types of gradients, which can have diverse effects on local and regional biodiversity. The objective of this dissertation was to identify how environmental heterogeneity gradients influence local and regional biodiversity and species composition in natural and experimental communities. For Chapter 1, I conducted a baseline study in which I surveyed crustacean communities from freshwater and saline wetlands from three study areas, which I refer to as metacommunities, across the Nebraska Sandhills to identify trends in species biodiversity and occurrences in association with local and regional environmental conditions. I found that the alpha richness of freshwater wetlands and metacommunity gamma richness decreased in metacommunities with lower abundances of freshwater wetlands and higher abundances of saline wetlands. For Chapter 2, I surveyed wetland crustacean egg banks from the same systems in Chapter 1, and I found that the egg banks exhibited similar patterns in biodiversity as the emergent crustacean communities surveyed in Chapter 1, and the emergent and egg bank metacommunity structures were strongly associated with the salinity gradient. I hypothesized that the decline in freshwater wetland and metacommunity biodiversity was caused by the decrease in the relative abundance of freshwater habitat patches across the landscape and the increase in the environmental contrast between the freshwater and saline wetlands. I tested this hypothesis in Chapter 3 by using mesocosms to develop experimental metacommunities that were structured along gradients of freshwater habitat abundance and environmental contrast between freshwater and saline patches. I found that my hypothesis was partially supported in that the species richness was significantly lower in freshwater communities and metacommunities from saline-dominated metacommunities. For Chapter 4, I tested a different type of heterogeneity by introducing invasive zebra mussels to experimental metacommunities to generate a disturbance-intensity gradient. I found that dispersal from undisturbed communities in heterogeneous metacommunities were able to mitigate species loss in the disturbed communities. Different sources and levels of environmental heterogeneity will generate different patterns in local and regional biodiversity.
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