Electronic Theses and Dissertations

Identifier

217

Date

2011

Date of Award

3-29-2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Biology

Committee Chair

Scott B Franklin

Committee Member

Reza Pezeshki

Committee Member

Matthew J Parris

Committee Member

Duane D McKenna

Abstract

Community ecologists have been plagued for years to accurately determine historical disturbance regimes to gain a better understanding on the processes governing plant community assembly. Mississippi River islands provide a unique system to examine these processes due to the abundance of vast amounts of historical data. Natural studies were used to assess island morphological change following a major flood event and were also used to assess plant community composition along a disturbance gradient. Additionally, a greenhouse study was used to examine the effects of competition and flooding on the overall growth rates of three island ubiquitous plant species. Also, another greenhouse study was used to assess the competitive advantages conferred being the first to colonize following a major flood event.Islands did not appear to grow in elevation following a major flood event, however they did appear to move laterally within the main channel, with 3 of the 5 islands moving closer to the navigable portion of the river. Natural composition of plant communities followed the shifting limitations and intermediate disturbance hypotheses, with higher diversity found in the intermediate elevations. Niche was found to be controlling diversity at the most and least disturbed portions of the gradient, while neutral was found controlling at the intermediately disturbed portions of the gradient. The first greenhouse study, which examined competition and flooding effects on Amaranthus palmeri, Cyperus strigosus, and Xanthium strumarium growth showed that competition affects each species differently. X. strumarium appeared to be more negatively affected by competition when grown with conspecifics. Also, it was apparent that all species were more negatively affected by disturbance than competition in any combination. In a second study, it was apparent that order of arrival significantly affected competitive abilities of short-lived plants on the islands. Established individuals out-performed novel individuals in biomass accumulation. This suggests that early arrival confers competitive advantages even in such a stochastic system. Furthermore, early arrival could lead to greater seed production and ultimately greater propagule pressure on riverine islands. These results suggest that in order to fully understand how communities assemble, it is important to understand the disturbance history in terms of frequency and intensity and the role that species-specific interactions play to give rise to different dominant species in a community. These species-specific interactions are likely a result of a combination of niche and neutral controls and rules governing community assembly are dependent on the type of abiotic conditions and life cycle stage plants are in.

Comments

Data is provided by the student.

Library Comment

dissertation or thesis originally submitted to the local University of Memphis Electronic Theses & dissertation (ETD) Repository.

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