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Pendergast IV, Thomas H (2013) EXPLAINING PATTERNS OF DOMINANCE IN OLD-FIELD COMMUNITIES: TRADE-OFFS, FEEDBACKS, MUTUALISMS AND ENEMIES. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Although one of the oldest observations within ecology is that within communities there are few common species with many uncommon and rare species, the mechanisms that shape this relationship remain elusive. The primary explanations for repeated dominance in plant communities lie in competition theory, which predicts specific allocation to resource acquisition, low resource tolerance, colonization, and herbivore tolerance and resistance. Alternatively, soil
community feedback theory predicts positive plant-soil feedbacks to alter competitive dynamics and lead to dominance. Finally, specific mutualistic clades of the soil community, such as mycorrhizal fungi, may increase resource acquisition or herbivore tolerance, thus promoting positive feedback. To address these mechanisms that contribute to relative abundance and dominance, I used a light limited, old-field model system. Although these systems are relatively diverse, there is a striking pattern of repeated dominance by Solidago canadensis. By using a series of greenhouse and manipulative, long-term in situ experiments, I found no “smoking gun” mechanism to explain the dominance of So. canadensis, but rather an entire suite of processes
that likely contribute to relative abundance and the maintenance of diversity. I found no evidence of life history trade-offs across old-field species, with S. canadensis consistently violating long-standing theory by being the best light competitor, most shade tolerant, most
herbivore resistant, most herbivore tolerant, and among the fastest growing species. Looking belowground, I found that old-field plant species, even coexisting congeneric species, culture significantly different soil microbial communities, which altered plant performance, changed the
intensity of interspecific competition and reversed whether plant species were limited by conspecifics or heterospecifics. Although this mosaic of shifting competitive abilities due to soil feedbacks is predicted to maintain diversity, the ability of S. canadensis to grow well in its own and competitor soil communities may foster S. canadensis invasion and subsequent defense of territory. Finally, mycorrhizal fungi increased herbivore tolerance across old-field species, while having little or negative effects on plants in the absence of herbivory. This process may promote diversity within old-fields, but offers insight into how So. canadensis maintain dominance in the face of dozens of specialist herbivores.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Pendergast IV, Thomas Hthp5@pitt.eduTHP5
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairCarson, Walter Pwalt@pitt.eduWALT
Committee MemberRelyea, Rick Arelyea@pitt.eduRELYEA
Committee MemberTonsor, Stephen Jtonsor@pitt.eduTONSOR
Committee MemberTraw, Milton Bmbtraw@pitt.eduMBTRAW
Committee MemberRoyo De Sedas,
Date: 24 July 2013
Date Type: Publication
Defense Date: 28 February 2013
Approval Date: 24 July 2013
Submission Date: 19 April 2013
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 132
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: Dominance Trade-offs Competition Feedbacks Mycorrhiza Herbivory old-field
Date Deposited: 24 Jul 2013 19:18
Last Modified: 15 Nov 2016 14:12


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