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

• Author / Creator

  Roberts, David R.

• 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.

• Subjects / Keywords

  • North America
  • Climate change
  • Historical biogeography
  • Genetic diversity
  • Trees
  • Migration
  • Species distribution models

• Graduation date

  Fall 2013

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3Q974

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.