Demographic modeling of Hawaiian silverswords, and its implications for conservation

Persistent Link:
http://hdl.handle.net/10150/280173
Title:
Demographic modeling of Hawaiian silverswords, and its implications for conservation
Author:
Forsyth, Stacey Ann
Issue Date:
2002
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
Population viability analyses based on matrix population models provide important information for species management. These analyses enable biologists to predict future population size and structure, assess extinction risk, and identify the stages and transitions in a species' life history that have the largest effects on population growth rate (lambda). It is also possible, using these analyses, to weigh the relative effectiveness of different management strategies. In this study, I constructed a matrix population model for a threatened Hawaiian plant species, the Haleakala silversword (Argyroxiphium sandwicense ssp. macrocephalum), in order to assess the viability of this population under different disturbance and management regimes. Over five years, I assessed annual variation in seed set and quantified reproductive vital rates for use in a matrix model. These data were combined with long-term demographic data in order to construct a stage-based matrix model for the Haleakala silversword. Using this model, I examined temporal and spatial variation in silversword demography. I also used the model to evaluate management strategies for the Haleakala silversword and the related subspecies, the endangered Mauna Kea silversword (Argyroxiphium sandwicense ssp. sandwicense). Using deterministic and stochastic models, I compared the relative impacts of different threats on silversword persistence, and weighed the relative effectiveness of different management options. The Haleakala silversword was self-incompatible, and percent seed set was positively correlated with annual flowering plant abundance. Individuals were pollen-limited only in low flowering years, suggesting a pollinator-mediated Allee effect in this species. Seeds remained viable in the field for multiple years, suggesting that a seed stage should be incorporated into the matrix model. Reproductive output (e.g., number of capitula and capitulum size) was strongly correlated with rosette diameter, allowing for size-based estimates of reproduction. Vital rates and population growth rates varied over time and space. In all years and plots, adult survival had the greatest impact on lambda. Thus, factors influencing adult survival, such as browsing and outplanting, had larger effects on lambda than did factors influencing seed set. Management strategies aimed at increasing germination rates or adult survival rates will be most effective in ensuring the persistence of silversword populations.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Biology, Botany.; Biology, Ecology.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Ecology and Evolutionary Biology
Degree Grantor:
University of Arizona
Advisor:
Robichaux, Robert H.

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleDemographic modeling of Hawaiian silverswords, and its implications for conservationen_US
dc.creatorForsyth, Stacey Annen_US
dc.contributor.authorForsyth, Stacey Annen_US
dc.date.issued2002en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractPopulation viability analyses based on matrix population models provide important information for species management. These analyses enable biologists to predict future population size and structure, assess extinction risk, and identify the stages and transitions in a species' life history that have the largest effects on population growth rate (lambda). It is also possible, using these analyses, to weigh the relative effectiveness of different management strategies. In this study, I constructed a matrix population model for a threatened Hawaiian plant species, the Haleakala silversword (Argyroxiphium sandwicense ssp. macrocephalum), in order to assess the viability of this population under different disturbance and management regimes. Over five years, I assessed annual variation in seed set and quantified reproductive vital rates for use in a matrix model. These data were combined with long-term demographic data in order to construct a stage-based matrix model for the Haleakala silversword. Using this model, I examined temporal and spatial variation in silversword demography. I also used the model to evaluate management strategies for the Haleakala silversword and the related subspecies, the endangered Mauna Kea silversword (Argyroxiphium sandwicense ssp. sandwicense). Using deterministic and stochastic models, I compared the relative impacts of different threats on silversword persistence, and weighed the relative effectiveness of different management options. The Haleakala silversword was self-incompatible, and percent seed set was positively correlated with annual flowering plant abundance. Individuals were pollen-limited only in low flowering years, suggesting a pollinator-mediated Allee effect in this species. Seeds remained viable in the field for multiple years, suggesting that a seed stage should be incorporated into the matrix model. Reproductive output (e.g., number of capitula and capitulum size) was strongly correlated with rosette diameter, allowing for size-based estimates of reproduction. Vital rates and population growth rates varied over time and space. In all years and plots, adult survival had the greatest impact on lambda. Thus, factors influencing adult survival, such as browsing and outplanting, had larger effects on lambda than did factors influencing seed set. Management strategies aimed at increasing germination rates or adult survival rates will be most effective in ensuring the persistence of silversword populations.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectBiology, Botany.en_US
dc.subjectBiology, Ecology.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineEcology and Evolutionary Biologyen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorRobichaux, Robert H.en_US
dc.identifier.proquest3073218en_US
dc.identifier.bibrecord.b43468123en_US
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