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Explaining variation in insect herbivore control over plant communities

Cronin, James P (2007) Explaining variation in insect herbivore control over plant communities. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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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.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Cronin, James
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairCarson, Walterwalt@pitt.eduWALT
Committee MemberBledsoe, Anthonybledsoe@pitt.eduBLEDSOE
Committee MemberSiemann,
Committee MemberRelyea, Rickrelyea@pitt.eduRELYEA
Committee MemberTonsor, Stephen Jtonsor@pitt.eduTONSOR
Date: 26 January 2007
Date Type: Completion
Defense Date: 14 August 2006
Approval Date: 26 January 2007
Submission Date: 25 September 2006
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Biological Sciences
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: bottom-up control; community ecology; exploitation ecosystem hypothesis; green world hypothesis; phytophagous; plant tolerance; top-down control
Other ID:, etd-09252006-121458
Date Deposited: 10 Nov 2011 20:02
Last Modified: 15 Nov 2016 13:50


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