Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)




Michael E. Pfrender


Genotypic diversity within populations can have important evolutionary consequences, but the ecological effects of intraspecific genetic variation on community and ecosystem function have only been studied in a few systems. I present the results of a three-year study designed to address the ecological impacts of genotypic diversity in quaking aspen (Populus tremuloides Michx.), using aspen genotypes planted across genotypic diversity levels (monoculture and mixture) and watering treatment levels (well-watered and water-limited). First, I demonstrated that significant variation exists among genotypes for a wide range of growth, morphological and physiological traits, and quantified high heritability and coefficient of genetic variation values for those traits. This demonstrates that heritable phenotypic variation exists within an aspen population, which could potentially have community and ecosystem implications. Secondly, I collected ground-dwelling arthropods across experimental treatment levels to determine if there are any community-level implications of genotypic diversity and watering treatment. Ground-dwelling arthropods were significantly affected by the genotypic diversity × watering treatment interaction, such that arthropod taxonomic diversity was lowest in water-limited genotypic mixtures. This result runs counter to the bulk of the plant diversity-arthropod diversity literature, which predicts that plant and arthropod diversity should be positively correlated, and highlights the importance of environmental conditions in mediating the plant-arthropod diversity relationship. Lastly, I show that there are no overall effects of genotypic diversity or watering treatment on tree growth patterns. Instead, there are high levels of variation among genotypes in their responses to treatments (significant genotype × diversity × watering treatment interactions), which are often opposing in direction. I also show that there are significant collection site × diversity × watering treatment interactions, demonstrating that genotypes vary in their response to experimental treatments based in part on their original collection site conditions in the field. This study demonstrates that aspen populations contain high levels of genotypic diversity, but that the ecological effects of genotypic diversity are mediated by the environment (in this case, watering treatment) and can be considerably more complicated than found in most previous studies.