Population Dynamics Across the Range of the Southern Appalachian Endemic Plant, Prenanthes Roanensis

A species‟ range is composed of the set of locations in which populations persist. As such, birth and death rates, which influence population persistence, are important determinants of a species‟ range. However, little is known about how demographic rates vary between populations across a range, though such studies can be useful for understanding the processes that structure a species‟ range. The research in this dissertation examines spatial and temporal variation in demographic rates and population dynamics across the range of the Southern Appalachian endemic plant, Prenanthes roanensis (Asteraceae). A four year field study was conducted to parameterize integral projection models using demographic data from six populations: two at the northern periphery of the range, two in the center of the range, and two at the southern periphery of the range. The results show that population growth rates at the edge of the range are generally comparable to population growth rates in the center of the range. In addition, I demonstrate that vital rates differ substantially between populations in the same region of the range. Shifting from a latitudinal comparison to a population comparison, I show that annual variation is important to the persistence of some populations, as population growth rates can shift from decreasing to increasing between years. Survival of nonreproductive individuals can be consistently linked to variation in population growth rates, and therefore, population persistence. However, population persistence may also depend on suitable microsites within the populations, as reproductive vital rates vary between patches within a population. Lastly, I examine the effects of herbivores on population persistence throughout the range. I demonstrate that herbivores can reduce ii population growth rates considerably through seed loss, but that enhanced seed quality may ameliorate these negative effects in some populations. The results presented in this dissertation demonstrate a tremendous amount of variation at a local, rather than a latitudinal, scale due to differences among populations in their response to annual variation and to differences in herbivory. Overall, the results presented in this dissertation demonstrate that local site factors have a large influence on population persistence and, therefore, the range of this species.

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