UBC Theses and Dissertations

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UBC Theses and Dissertations

Conservation genetics of small populations Marr, Amy Beth


Many species of plants and animals exist in small populations because human activities have fragmented and reduced natural habitats. Individuals in small, relatively isolated populations tend to have lower survival and reproductive success due to inbreeding and loss of genetic variation. To reverse these genetic problems, some biologists have advocated managing rare species by building dispersal corridors among populations or by translocating individuals. However, conservation strategies that manipulate gene flow are risky. This thesis uses long-term data on a population of song sparrows to study the various genetic phenomena that can be vital to the biology and management of small populations. The data on the song sparrows (Melospiza melodia) of Mandarte Island are somewhat extraordinary because, since 1975, virtually all individuals have been colour-banded and there exists an extensive pedigree of the population. Chapter one introduces the study population, provides background on inbreeding depression and genetic drift, and discusses the objectives of this thesis. Chapter two describes the survival and reproductive success of immigrants and their descendants in the Mandarte Island song sparrow population. The performance differences between immigrant and native females and between F[sub i]s (birds with an immigrant and a native parent) and the average of immigrants and natives suggest that immigrants were disadvantaged by a lack of site experience, and that F[sub i]s benefited from heterosis. However, none ofthe gains experienced by F[sub i]s were seen in the subsequent generation, probably due to outbreeding depression. Chapter three uses a simulation model to demonstrate that errors in the pedigree cause errors in inbreeding coefficients and bias in inbreeding depression estimates. Chapter four tests for the interactive effects of inbreeding and environmental stress on four reproductive traits. It is shown that the eggs laid by inbred female song sparrows had particularly low hatching success during rainy periods. Pedigree error and interactions between inbreeding and environmental stress are two factors that may contribute to variation in inbreeding depression estimates across studies. Chapter five explains why the findings for this study population and other academic research on inbreeding and outbreeding are relevant to the management of small populations of conservation concern.

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