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UBC Theses and Dissertations

An analysis of ecological traits as reproductive barriers between the MacGillivray’s (Geothlypis tolmiei) and Mourning (G. philadelphia) warblers Porter, Alison Nicole


Speciation in birds is often thought to be influenced by ecological diversification, which may form barriers to reproduction between species. Ecological selection can act as a premating barrier by reducing the chance of interactions between species, or as a postmating barrier if hybrids have ecological traits that are unfavourable. My objective in this study is to understand the role of ecological traits in maintaining isolation between MacGillivray’s (Geothlypis tolmiei) and Mourning warblers (G. philadelphia), which are two songbird species that form a narrow hybrid zone in northeastern British Columbia. I generate ecological niche models for each species to investigate whether the niche might have a role in explaining the location and width of the hybrid zone by comparing niche and range limits, and whether there is evidence for niche divergence. I show that the species have niches that are similar but have diverged in climatic variability and precipitation measures. These differences may partly explain why the niche models predicted that geographic regions within a species’ own range were the most suitable for that species. The contact zone was the only region where both models predicted high suitability, suggesting that hybridization occurs only where conditions are suitable for both species. I also present two analyses of how genotype is related to ecological characteristics in the hybrid zone. I use the niche models to predict the relative suitability of locations where birds occupied breeding territories in the hybrid zone and compared the relative scores among a gradient of hybrid genotypes. At those same hybrid zone territories I measure microhabitat characteristics of territories and conducted a Principal Component Analysis to examine whether there is a relationship between microhabitat of territories with genotype. I found no evidence that genotype was related with ecological traits in the hybrid zone. This suggests that when under the same ecological conditions the two species are ecologically equivalent, and that hybrids likely do not experience a disadvantage in terms of the ecological traits of their breeding territories. Overall, these results suggest that niche divergence likely had only a small role in the diversification between the MacGillivray`s and Mourning warblers.

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