Persistent Link:
http://hdl.handle.net/10150/186630
Title:
Effects of competitive symmetry on populations of annual plants.
Author:
Schwinning, Susanne.
Issue Date:
1994
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:
I examine the effects of competitive symmetry on annual plant populations through growth rate analysis, simulation modeling and experiments. I distinguish symmetric from asymmetric competition at several spatial and temporal scales. Local symmetry is defined by the way competitors divide resources in spaces where they overlap. Whole-plant symmetry is defined by the comparison of the total resource interception of competitors. Through plant growth analysis I show that local symmetry of competition is not identical to whole-plant symmetry of competition. Whole plant symmetry of competition also depends on the allometry of space occupancy and, under some circumstances, on the spatial distribution of the limiting resource. If plants capture space more slowly than they accumulate biomass, competition is symmetric at low density and asymmetric at high density. The local symmetry of competition determines the magnitude of the density response. These results extend to the population-wide, seasonally-integrated level, where the symmetry of competition is expressed in the slope of empirical distribution-modifying functions (DMFs: regression functions of the log-transformed relative biomass increments of individuals between the seedling stage and maturity on the log-transformed seedling biomass). A neighborhood-based simulation model shows that the slopes of empirical DMFs depend mostly on density and local competitive symmetry. Random variation of height, site quality and plant spacing affect DMFs only slightly, but affect population size structure greatly. I confirm these simulation results in field experiments with populations of millet (Pennisetum americanum) and cowpea (Vigna unguiculata). Millet plants were grown isolated, at low density (10,000 plants ha⁻¹, and at high density (20,000 plants ha⁻¹. Cowpea plants were grown isolated, or as single cowpea plants within stands of low and high density millet. In both species and in two experimental years the DMF slopes of high density populations were greater than the DMF slopes of isolated plant populations. However, the DMF slopes of high density plants were not always positive. These results suggest that the population-wide, seasonally-integrated symmetry of competition may vary between years, but that the increase of the DMF slope with density may be quite general.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Dissertations, Academic.; Ecology.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Ecology and Evolutionary Biology; Graduate College
Degree Grantor:
University of Arizona
Committee Chair:
Robichaux, Robert H.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleEffects of competitive symmetry on populations of annual plants.en_US
dc.creatorSchwinning, Susanne.en_US
dc.contributor.authorSchwinning, Susanne.en_US
dc.date.issued1994en_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.abstractI examine the effects of competitive symmetry on annual plant populations through growth rate analysis, simulation modeling and experiments. I distinguish symmetric from asymmetric competition at several spatial and temporal scales. Local symmetry is defined by the way competitors divide resources in spaces where they overlap. Whole-plant symmetry is defined by the comparison of the total resource interception of competitors. Through plant growth analysis I show that local symmetry of competition is not identical to whole-plant symmetry of competition. Whole plant symmetry of competition also depends on the allometry of space occupancy and, under some circumstances, on the spatial distribution of the limiting resource. If plants capture space more slowly than they accumulate biomass, competition is symmetric at low density and asymmetric at high density. The local symmetry of competition determines the magnitude of the density response. These results extend to the population-wide, seasonally-integrated level, where the symmetry of competition is expressed in the slope of empirical distribution-modifying functions (DMFs: regression functions of the log-transformed relative biomass increments of individuals between the seedling stage and maturity on the log-transformed seedling biomass). A neighborhood-based simulation model shows that the slopes of empirical DMFs depend mostly on density and local competitive symmetry. Random variation of height, site quality and plant spacing affect DMFs only slightly, but affect population size structure greatly. I confirm these simulation results in field experiments with populations of millet (Pennisetum americanum) and cowpea (Vigna unguiculata). Millet plants were grown isolated, at low density (10,000 plants ha⁻¹, and at high density (20,000 plants ha⁻¹. Cowpea plants were grown isolated, or as single cowpea plants within stands of low and high density millet. In both species and in two experimental years the DMF slopes of high density populations were greater than the DMF slopes of isolated plant populations. However, the DMF slopes of high density plants were not always positive. These results suggest that the population-wide, seasonally-integrated symmetry of competition may vary between years, but that the increase of the DMF slope with density may be quite general.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectDissertations, Academic.en_US
dc.subjectEcology.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineEcology and Evolutionary Biologyen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.chairRobichaux, Robert H.en_US
dc.contributor.committeememberWalsh, J. Bruceen_US
dc.contributor.committeememberSchaffer, William M.en_US
dc.contributor.committeememberVleck, David J.en_US
dc.contributor.committeememberChesson, Peteren_US
dc.identifier.proquest9424963en_US
dc.identifier.oclc722474628en_US
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