Relationships Between Population Variation and Ecological Variability
Zangerl, Arthur Rainer
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https://hdl.handle.net/2142/68209
Description
Title
Relationships Between Population Variation and Ecological Variability
Author(s)
Zangerl, Arthur Rainer
Issue Date
1981
Department of Study
Plant Biology
Discipline
Botany
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Botany
Language
eng
Abstract
The recognition that populations generally harbor large quantities of variation has resulted in a wide ranging effort to relate this variation to that of the environment. There have been primarily two approaches to the question. The population genetics approach is to examine the level of population variation that can be maintained by an environment with a given degree of heterogeneity. The ecological approach is to determine the relationship between a population's variation and its ability to occupy a variety of potential environments. Both approaches are pursued in this thesis. The population genetics approach is combined with a proposed stress-variation hypothesis. Stressful environments are predicted to yield populations with reduced levels of variation. Levels of variation were measured in populations of Amaranthus retroflexus and Abutilon theophrasti after four generations of exposure to stress gradients of density, diversity and soil moisture.
The results for the phosphoglucoisomerase (PGI) locus of Amaranthus retroflexus were in substantial agreement with predictions. Populations exposed to density stress, suboptimal and supraoptimal soil moistures all experienced reductions in variation. The exceptions are the moderate moisture conditions which also experienced reductions in variation and the diversity treatments, all of which maintained variation. These apparent exceptions are discussed. Patterns of morphological and physiological variation in both A. retroflexus and Abutilon theophrasti were consistent although not conclusively with the stress model.
A high degree of correlation was discovered between PGI genotype in Amaranthus retroflexus and morphological and physiological characters. This association is argued to be the result of genetic coadaptation. These genotypes were also found to have other physiological differences including differing germination responses along gradients of oxygen and differing reproductive success along moisture gradients. In view of such differences the importance of genetic variation to niche breadth is questioned and instead a theoretical framework is presented which emphasizes the role of various components of genotypic diversity to niche breadth of populations.
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