Degree

Doctor of Philosophy (PhD)

Department

Biological Sciences

Document Type

Dissertation

Abstract

Non-random spatial patterns within species are commonly observed in nature. Identifying spatial patterns of individuals within populations can give insight into processes regulating those populations and may indicate processes operating at community and ecosystem levels. Non-random spatial patterns of sessile organisms and dominant species are especially important for determining ecological processes structuring those populations. C4 tussock-forming grasses (bunchgrasses) are dominant competitors and foundation species in pine savanna groundcover plant communities. Characterizing the spatial patterning of dominant bunchgrasses informs our understanding of processes regulating bunchgrass populations and indicates how bunchgrass populations may influence community assembly and ecosystem function in pine savannas. In this dissertation I characterize the spatial patterning of dominant bunchgrasses in pine savanna groundcover plant communities and explore mechanisms responsible for generating non-random bunchgrass spatial patterns.

I used a combination of observational field studies and experiments to examine spatial patterning of dominant bunchgrasses. First, I characterized the spatial patterns of dominant bunchgrass species in natural populations in pine savannas throughout the gulf coastal plain. Second, I observed changes in bunchgrass spatial patterning over time using a restored pine savanna chronosequence. Last, I examined the effect of distance from a large bunchgrass tussock on the performance of small bunchgrass tussocks and on the availability of above and belowground resources.

My results show that dominant bunchgrasses are universally overdispersed at the plant-neighborhood scale in natural populations. Furthermore, the scale of overdispersion of bunchgrass tussocks increases over time. Finally, there was a significant distance-dependent negative effect of large bunchgrass tussocks on neighboring bunchgrass performance and on availability of belowground resources. This indicates that a scale-dependent negative feedback is regulating bunchgrass populations and is generating overdispersed spatial patterning of bunchgrasses observed in nature.

We conclude that density-dependent population regulation generates overdispersed spatial patterns of dominant bunchgrasses in pine savanna groundcover plant communities. The overdispersed pattern of dominant bunchgrasses may play a role in the maintenance of high biodiversity of pine savanna groundcover vegetation by reducing the frequency of interactions among subordinate species. Furthermore, the overdispersed pattern of dominant bunchgrasses likely affects ecosystem function by promoting fire disturbance via continuous distribution of fine fuels.

Date

11-15-2019

Committee Chair

Harms, Kyle

Available for download on Wednesday, October 28, 2026

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