Date of Award

Spring 1-1-2015

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Museum and Field Studies

First Advisor

Dena M. Smith

Second Advisor

Cesar R. Nufio

Third Advisor

Herbert W. Meyer

Abstract

The fossil record provides an excellent study system for understanding how organisms respond to climate change free from human interference. In this study I test the hypothesis that global cooling altered the diversity of Coleoptera (beetles) in the Western Interior of North America during the middle Eocene. This hypothesis was addressed by comparing two fossil beetle assemblages from the Green River Formation of Colorado. These assemblages bracket a ~2.5 million year (m.y.) cooling interval that followed a period of maximum warming (~52-50 Ma) in the Cenozoic. Based on modern biogeographic patterns of insect diversity, I predicted overall community richness decreased and evenness increased over time, and that taxon-specific feeding strategies drove differential responses to cooling, with non-herbivores showing a greater decrease in richness and abundance than herbivores. Compositional turnover was also anticipated with time and cooling.

In total, 580 specimens were sorted into morphospecies within the Carabidae, Staphylinidae, or Curculionoidea (weevils). By using individual-based rarefaction and rank abundance distributions, I found that total community richness and evenness did not significantly change with time/cooling. This pattern also held when beetle data were parsed by feeding guild and taxon. Non-herbivores became more abundant, and there is growing evidence that compositional turnover also occurred with time. One factor complicating comparisons of raw abundances and compositional change was undersampling, which was estimated to be more than double the observed richness for both beetle collections.

This study shows that the response of beetle communities to climate change is complex, and that resultant diversity patterns are sensitive to both ecologic and taxonomic resolution. Moreover, if the beetles assessed here are taken as a representative subset of the entire Green River insect fauna, the environment surrounding ancient Lake Uinta likely accommodated an exceptionally speciose insect community during the middle Eocene. By comparing the diversity and composition of this fossil beetle community to others known from the Western Interior, a more holistic interpretation of how insects respond to the different rates and magnitudes of global climate change should crystallize.

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