With the introduction of metacommunity theory, the field of community ecology expanded its scope to include patterns and processes beyond the scale of local communities. Dispersal, or the movement of organisms between sites, can play an influential role in generating patterns of community assembly and stability. However, little is known about the role of dispersal in structuring and stabilizing freshwater communities. For my dissertation, I conducted a literature review of dispersal in stream metapopulations and metacommunities. Our current knowledge of the movement of freshwater taxa is limited due to difficulties in accurately monitoring dispersal. We have inferred the role of dispersal based primarily on organismal-based and graph-based proxies, although the body of work in modeling and experimental research is growing. Future research should incorporate innovative methods to directly monitor dispersal at finer spatial and temporal scales. To address this knowledge gap, we experimentally manipulated dispersal mode (aerial and drift) alongside the magnitude of dispersal (network location as a proxy) to investigate the role of these components of dispersal in community assembly and multiple metrics of stability. The results of my experiment suggest both factors may play a role in community assembly and stability patterns in stream metacommunities. Lastly, I conducted a mesocosm experiment with zooplankton mesocosms to investigate if biodiversity can generate asynchronous patterns of community dynamics that contribute to stability. There was a positive biodiversity-asynchrony relationship that, in turn, generated higher levels of stability. This effect was strongest in communities connected via dispersal. Overall, my dissertation demonstrates that dispersal plays a role in the assembly and stability of freshwater communities.
Doctor of Philosophy
Freshwater ecosystems and the abundance and richness of life that they support are threatened under global environmental change. One factor that may help maintain the diversity of stream-dwelling species is dispersal, or the movement of organisms between sites within networks of freshwater communities. The influence of dispersal on the formation and stability of freshwater communities is poorly understood. To determine the state of the science, I conducted a literature review on the study of dispersal in stream networks. We have only recently developed a limited knowledge of the direct movement of freshwater species within networks. The majority of what we know is deduced from patterns of diversity, the traits of organisms, or theoretical modeling. More direct measures of dispersal are needed to understand the dispersal of freshwater organisms. To address this knowledge gap, I conducted an experiment with streamside flumes throughout a stream network where I manipulated how a macroinvertebrate could colonize, or join, a stream community. I found that both position in a network and the use of various methods of colonization affect patterns of diversity and how stable stream communities are. Finally, I conducted an experiment where I manipulated the number of zooplankton and environmental conditions to detect the influence of dispersal on community dynamics and stability. Communities connected via dispersal had the highest level of asynchrony in dynamics and these community dynamics, in turn, produced the greatest amount of community stability. Overall, these findings demonstrate the role of dispersal in the biodiversity and stability of freshwater communities.