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Biogeographic histories and genetic diversity of western North American tree species: implications for climate change Open Access


Other title
North America
genetic diversity
historical biogeography
climate change
species distribution model
Type of item
Degree grantor
University of Alberta
Author or creator
Roberts, David R.
Supervisor and department
Andreas Hamann (Renewable Resources)
Examining committee member and department
Andrew Bush (Earth and Atmospheric Science)
Glen Armstrong (Renewable Resources)
Jack Williams (Geography, University of Wisconsin at Madison)
Erin Bayne (Biological Science)
Scott Nielsen (Renewable Resources)
Department of Renewable Resources
Conservation biology
Date accepted
Graduation date
Doctor of Philosophy
Degree level
Over the last two million years, the evolution of North American tree species, subspecies, and genetic varieties has taken place in a constantly changing landscape often dominated by extensive ice sheets and restricted temperate climate environments. Here, I approximately reconstruct post-glacial vegetation histories and glacial refugia of western North American trees using species distribution models to test biogeographic hypotheses regarding the existence of glacial refugia in Beringia, the evolution of subspecies in widespread conifers, the origin of Pacific Northwest inland rainforests, and levels of modern genetic diversity. The first two chapters have a methodological emphasis, where I select and test a variety of species distribution models for their accuracy and robustness. Validations against 3,571 pollen and fossil records from 835 study sites indicated fair accuracy for most techniques (AUCs around 0.75). Ecosystem-based modelling approaches outperformed in specificity statistics and robustness against extrapolations far beyond training data, suggesting that they are well suited to reconstruct historical biogeographies. Evaluations at the biome level indicated that species distribution models could approximately reconstruct biomes for the mid- to late-Holocene but became unreliable in the Late Pleistocene due to the emergence of no-analogue climates. However, the limitation applied primarily to non-forested biomes. Using a set of three robust species distribution modelling techniques, I investigate how modern genetic diversity and genetic structure was shaped by refugial history, using published estimates of allelic richness and expected heterozygosity for 473 populations of 22 tree species. Species with strong genetic differentiation into subspecies and varieties had widespread and large glacial refugia, while species with restricted refugia showed no differentiation and little genetic diversity. In a regression tree analysis, 66% of allelic richness could be explained by the total size of glacial refugia, while expected heterozygosity was best explained by the number of glacial refugia. A comparison of projected past and future habitats showed that future migration requirements were much faster than, but highly correlated with, past migration requirements a cross 24 tree species. Populations in certain localities may be at risk of maladaptation due to the inability of gene flow to keep pace with the migration of climate habitats.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Roberts, D. R. and A. Hamann (2012). "Predicting potential climate change impacts with bioclimate envelope models: a palaeoecological perspective." Global Ecology and Biogeography 21(2): 121-133.Roberts, D. R. and A. Hamann (2012). "Method selection for species distribution modelling: are temporally or spatially independent evaluations necessary?" Ecography 35: 792-802.

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