Research has repeatedly demonstrated that herbivores can, at some times and in some places, control the distribution and abundance of plants. Consequently, explaining variation in herbivore control over plant communities is a central goal in ecology and evolutionary biology. Two major challenges have prevented theoretical progress in this area of research. First, although there are numerous hypotheses that attempt to explain variation in herbivore control over plant communities, theoretical reviews have focused on a single hypothesis. Thus, it has been unclear where these herbivore control hypotheses diverge in their predictions and rationale. Second, herbivore control hypotheses base their explanations on highly correlated vegetation characteristics, namely net primary productivity (NPP), plant vigor, plant apparency, plant tissue nitrogen, plant defenses, plant tolerance, and host plant concentration. Consequently, interpretations of field experiments and meta-analyses have been equivocal. To address the first problem, I simultaneously reviewed herbivore control hypotheses and their predictions and rationale. I demonstrate that these hypotheses can be synthesized into four central hypotheses based on NPP, plant size, resource availability, and host stem density. This provides researchers with few vs. many herbivore control hypotheses. To address the second problem, I simultaneously tested these hypotheses by experimentally manipulating resource availability, total stem density, plant species composition, and herbivore abundance under field conditions. I then monitored the response of herbivore abundance, damage to plants, and the reduction in plant mass due to herbivory. The experiments demonstrated that herbivory caused the strongest reductions in mean stem mass where per stem resource availability was lowest, regardless of where herbivore abundance and damage was greatest. This result supports the plant tolerance based resource availability hypothesis, which assumes that the ability of plants to tolerate herbivory increases as resource availability increases. In addition, herbivore control over both simple plant communities (i.e., monocultures) and complex plant communities (i.e., polycultures) was due to herbivory on the dominant plant species, Solidago canadensis. Together, these results suggest that future herbivore control hypotheses should focus on the effect of per-capita resource availability on the ability of dominant plants to tolerate herbivory.
| Identifer | oai:union.ndltd.org:PITT/oai:PITTETD:etd-09252006-121458 |
| Date | 26 January 2007 |
| Creators | Cronin, James P |
| Contributors | Walter Carson, Rick Relyea, Anthony Bledsoe, Stephen J Tonsor, Evan Siemann |
| Publisher | University of Pittsburgh |
| Source Sets | University of Pittsburgh |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.pitt.edu/ETD/available/etd-09252006-121458/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Pittsburgh or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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