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Evolutionary EcologyConcepts and Case Studies$
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Charles W. Fox, Derek A. Roff, and Daphne J. Fairbairn

Print publication date: 2001

Print ISBN-13: 9780195131543

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780195131543.001.0001

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Nature and Causes of Variation

Nature and Causes of Variation

(p.3) 1 Nature and Causes of Variation
Title Pages

Susan J. Mazer

John Damuth

Oxford University Press

The field of evolutionary ecology is at its core the study of variation within individuals, among individuals, among populations, and among species. For several reasons, evolutionary ecologists need to know the causes and the effects of variation in traits that influence the performance, behavior, longevity, and fertility of individuals in their natural habitats. First, to determine whether the conditions for evolution by natural selection of traits of interest are fulfilled, we need to know the degree to which the phenotype of a trait is determined by the genetic constitution (or genotype) of an individual and by the environment in which an individual is raised. Second, to predict whether and how natural selection will cause the mean phenotype of a trait in a population to change from one generation to the next, we must understand the ways in which an individual’s phenotype (for this trait) influences its genetic contribution to future generations (i.e., its fitness). Third, to understand why the phenotype of a given trait influences an individual’s fitness, we need to know how the trait affects an individual’s ability to garner resources for growth or reproduction, to avoid predation, to find mates, and to reproduce successfully. Finally, to evaluate whether the phenotypic differences we observe among populations and species may represent the long-term outcome of evolution by natural selection, we must understand how different phenotypes perform under different environmental conditions. In sum, with an understanding of the causes and consequences of phenotypic variation within and among populations, we can detect evolutionary processes operating at a variety of ecological levels: within random-mating populations; within and among subpopulations distributed over a species’ geographic range; and even among multispecies associations. These goals, however, require a clear understanding of the nature of phenotypic variation. The aim of this chapter and the next is to illustrate that the richness of evolutionary ecology has increased in direct proportion to our understanding of the multiple causes of intraspecific phenotypic variation.

Keywords:   Allozymes, Cephalic weaponry, Dimorphism, Epistasis, Heritability, Inducible defense, Liability, Modular organs, Norm of reaction

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