The term "interaction" in evolutionary biology and ecology
describes the relationships among variables in two classes of causal
models. In the first, "interaction" refers to the influence of a
single putatively causal variable on a variable of interest. In the
second class of models, the term applies when a third variable
mediates the relationship between two variables in the first class of
models. The development of multi-factor causal models in evolutionary
biology and ecology represents a stage in the construction of theory
that usually follows from complexities discovered in single-factor
analyses. In this thesis, I present three cases that illustrate how
results of simple single-factor models in the population genetics and
community ecology of seaweeds may be affected by incorporation of a
second causal factor.
In Chapter II, we consider how the effect of natural selection
on genetic variability in seaweeds and other plants may be mediated by
life history variation. Many seaweeds have haplodiplontic life
histories in which haploid and diploid stages alternate. Our
theoretical analysis and review of the electrophoretic literature show
that the level of genetic polymorphism in haplodiplonts is not
necessarily reduced relative to that in diploids. In Chapter III, I
take an experimental approach to understanding how herbivory may
mediate the effect of desiccation on the upper intertidal limit of a
red alga, Iridaea cornucopiae. Iridaea appears to be grazer-limited
in dry, but grazer-dependent in moist environments, suggesting that a
third factor may mediate the interaction of desiccation and herbivory.
Finally, in Chapter IV, we consider research strategies for studying
how the outcome of competitive interactions is affected by seaweed
traits. Some of the problems that arise in applying simple models of
competition to plants suggest the need for theory that explicitly
incorporates plant traits in two- (or more) factor models of
interspecific competition. In particular, we note that unique traits
of seaweeds require development of new approaches to understanding
competition.
Single-factor causal models represent an indispensable stage in
the development of evolutionary and ecological theory. Properly
conceived theoretical and empirical studies focus attention on the
assumptions under which such models will hold and suggest lines of
inquiry that ultimately lead to the integration of additional causal
factors in conceptual models of natural processes. Identifying the
circumstances under which simple models will suffice remains one of
the most important challenges of evolutionary and ecological
scholarship. / Graduation date: 1993
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/36861 |
| Date | 18 June 1992 |
| Creators | Olson, Annette M. |
| Contributors | Lubchenco, Jane |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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