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Title The Evolutionary Stability of Partial Migration
Publication Date
Date Available
Date Accessioned
Degree PhD
Degree Level doctoral
University/Publisher Oregon State University
Abstract Natural selection, in its most basic form, is described as a process in which traits increase or decrease in frequency depending on their fitness, and only the trait with the highest fitness will remain in the population. Yet, populations rarely have a single `optimal' trait. The way natural selection maintains this observed variation within populations has been a keen focus of evolutionary biologists. In the following chapters, I focus on how natural selection maintains a form of phenotypic variation referred to as `partial migration'. Partial migration is the coexistence of migratory and non-migratory phenotypes, and is found in a wide variety of taxa. I found that some, but not all forms of density-dependent competition can lead to the evolution and maintenance of partial migration (i.e., partial migration as an evolutionarily stable strategy (ESS) and convergent stable strategy (CSS)). Whether density-dependent competition allows for partial migration as an ESS and a CSS depends on how it influences the relative fitnesses of the phenotypes. If competition changes the relative fitnesses in opposing directions, then it will allow for partial migration. If it affects the relative fitnesses in the same direction, it will not. I then apply these results to a fish species of conservation and commercial concern: Oncorhynchus mykiss, or steelhead and rainbow trout. I demonstrate how female steelhead and rainbow trout competing separately for spawning habitat can still be subject to frequency-dependent selection and how this allows for partial migration. The frequency-dependent selection also results in strong feedbacks between survival and reproduction, which produces a non-linear response in the migration propensity ESS and CSS. In practical terms, this means that conservation or management actions may not affect the population as expected, and measuring the propensity for migration in wild populations is notoriously difficult. To address this difficulty, I develop a method to measure the propensity for migration in wild populations that can be used to test the predicts I generated in the two previous chapters. The method is called sex-ratio balancing and it relies on a fundamental relationship between sex ratios and the propensity for migration. Sex ratios are much easier to measure than the propensity for migration and the ease of measurement makes this method valuable for studying many different partially migratory taxa.
Subjects/Keywords partial migration
Contributors Lytle, David (advisor); Jordan, Chris (committee member)
Language en
Country of Publication us
Record ID handle:1957/61591
Repository oregonstate
Date Retrieved
Date Indexed 2017-06-30
Grantor Oregon State University
Issued Date 2017-06-26 00:00:00
Note [] Graduation date: 2017; [peerreview] no;

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