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theses

Invasive species have serious ecological and economic impacts worldwide. They are known to decrease biodiversity, disrupt ecosystem functioning, and displace native species. Much of the research focused on invasive species has tried to characterizing traits of invasive species, to characterizing the communities they invade, as well as competition for resources, and lack of natural enemies. Many times, these studies occur after a species is fully entrenched and therefore hard to eradicate or control. When possible, it is critical to identify and study the next potential invasive species before they become a significant invader. My dissertation research investigates dispersal strategies of two newly invasive viburnum plant species. The focus is to understand the primary mechanisms for seed dispersal, explore spatial distribution patterns of the invasion, and to determine the genetic diversity of naturalized populations through a landscape genetics approach. By investigating V. dilatatum and V. sieboldii during the early stages of their invasion, my dissertation will have broad applications for land managers who may find these species in their parks by providing them with the best practices for controlling their spread. My two motivating questions are as follows: are the dispersal “strategies” employed by closely related species comparable and what “strategy” leads to greater success at invading communities?
Chapter one investigated how fruit nutritional content influenced dispersal. We found that V. sieboldii fruit was dispersed during fall migration, primarily by Gray Catbirds (Dumetella carolinensis) and that V. dilatatum fruit was dispersed in the winter, mainly by American Robins (Turdus migratorius). The implications for dispersal were that V. sieboldii has a higher probability for long-distance seed dispersal than V. dilatatum which may explain why V. sieboldii is more widely distributed than V. dilatatum. In chapter two, we used point pattern analysis to detect local patterns of species distribution. The data suggests that V. sieboldii most likely relies on clonal spread at distances under three meters but is likely dispersed by birds at distances from eight to twelve meters. While V. dilatatum likely spreads by fruit both at distances under four meters by seedfall and by bird-enhanced seed dispersal at distances between six and thirteen meters. Chapter three explored how dispersal influences gene flow between locations. We found that all V. sieboldii populations freely experience gene flow and V. dilatatum is structured into two populations likely due to the differences in bird-enhanced dispersal. This suggest that while migratory birds are likely responsible for seed dispersal between populations of V. sieboldii, resident birds may have large enough ranges to disperse seeds between populations of V. dilatatum. This dissertation illustrates the need for a trait-based approach in context of a species natural history for assessing newly invasive species. Studies such as mine provide supporting evidence for this and also provide a baseline to ask more interesting questions about the system.

ETD_9269

Ph.D.

Includes bibliographical references

by Anthony C. Cullen

doi:10.7282/t3-pj1a-ej46

ETD doctoral

The author owns the copyright to this work.