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Grassland plant community assembly: The role of environmental heterogeneity, evolutionary history, competition, and pollination Open Access


Other title
plant ecology
niche conservatism
community phylogenetics
Type of item
Degree grantor
University of Alberta
Author or creator
Bennett, Jonathan A.
Supervisor and department
Cahill, James (Biological Sciences)
Examining committee member and department
Suding, Katherine (Environmental Science, Policy, & Management, UC Berkeley)
Manson, Jessamyn (Biological Sciences)
Proctor, Heather (Biological Sciences)
Hall, Jocelyn (Biological Sciences)
Department of Biological Sciences
Date accepted
Graduation date
Doctor of Philosophy
Degree level
Plant community assembly is not a simple process; any factor that can affect the recruitment or coexistence of individuals can alter the outcome (e.g. nutrients, symbionts). In this thesis, I address a diverse subset of these potential factors, focusing on environmental variation, evolutionary history, competition, and pollination. I begin by testing whether evolutionary history constrains how species respond to 14 environmental factors. From this study, I conclude that evolutionary history has a weak effect on how species respond to changes in their environment, but that it can be important under certain circumstances. Next, I test whether competition is stronger when neighboring species are more related, which is hypothesized to leave a phylogenetic signature on plant communities if competition is important in community assembly. Competition did not increase with relatedness, potentially because competition was diffuse. As such, there was no measurable signature within the community. From these results, I expand existing theory to explore the conditions where competition should leave a phylogenetic signature. The importance of competition in community assembly is expected to increase or remain invariant with productivity, depending on the theory. I tested these ideas using a competition experiment with 22 species, but found competition declined with productivity, which is consistent with theories emphasizing resource supply and demand. Community assembly can also be dictated by recruitment, but few studies address how pollination, an important step in the recruitment process, varies across the community. I used a broad survey to examine whether pollination varied with environmental conditions and a manipulative experiment to test whether pollination can be predicted by abundance changes. Both flowering and flower visitation were highly dependent on environmental conditions and while they were correlated with abundance, they responded independently to environmental manipulations. This suggests that pollination and potentially seed production may become decoupled from abundance under a variety of conditions. Combined, my results suggest that many processes contribute to community assembly and that each of these processes is only important under certain conditions. More generally, my results cast doubt on the presence of general assembly rules that are applicable beyond the very smallest scales.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Bennett J.A. & Cahill J.F., Jr. (2012). Evaluating the relationship between competition and productivity within a native grassland. PLoS ONE, 7, e43703.Bennett J.A., Lamb E.G., Hall J.C., Cardinal-McTeague W.M. & Cahill J.F. (2013). Increased competition does not lead to increased phylogenetic overdispersion in a native grassland. Ecology Letters, 16, 1168-1176.

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