Date of Award
Doctor of Philosophy (PhD)
Ecology & Evolutionary Biology
Christy M. McCain
M. Deane Bowers
Understanding the distribution of species is a central question in biology and a critical challenge for effective conservation. Broad patterns of biodiversity have been of interest for many decades, driving the development of a large body of theory. We now have the data and tools to more robustly evaluate many of the proposed patterns and mechanisms. In this dissertation, I assess the assumed patterns of diversity and elevational range size across latitudes and elevations with ants as a focal taxon. In Chapter II, I use well-sampled published datasets from across the globe to establish the main patterns of ant richness across elevations and to evaluate several diversity hypotheses. In Chapter III, I develop a multi-scale hierarchical Bayesian community occupancy model to rigorously test additional hypothesized diversity drivers in Colorado ants along four elevational gradients. In Chapter IV, I combine global datasets with data from Colorado to determine whether mean ant elevational range size increases with latitude and with elevation, whether any patterns are driven by temperature variation, and whether the assumed spatial patterns of temperature variation are well-founded. With the four Colorado gradients, Chapter V uses patterns of beta diversity at different taxonomic resolutions to address the hypothesis that competition controls diversity at low elevations, while an increasingly harsh climate limits diversity at higher elevations. Lastly, in Chapter VI, I ask whether ant species in Colorado’s Front Range have shifted their elevational distribution in response to climatic warming over the past 50 years, and whether any shifts are exacerbated by additional anthropogenic impacts. I find that ant richness is most often highest at intermediate elevations, driven by multiple factors including primary productivity and phylogenetically conserved temperature preferences. Despite notoriously fierce interactions among ants, there is little evidence that interspecific competition plays a role in broader elevational patterns. Seasonal temperature variation does drive an increase in mean elevational range size across latitudes. However, there is no consistent elevational pattern in temperature variation, and thus no consistent elevational pattern in mean range size. Though climate change-induced elevational shifts vary among species, an average uphill shift was detected, broadly consistent with the observed pattern of warming along the elevational gradient.
Szewczyk, Timothy Michael, "Diversity & Elevational Ranges: Evaluating Theory Across Spatial Scales in Montane Ants" (2017). Ecology & Evolutionary Biology Graduate Theses & Dissertations. 94.
Available for download on Saturday, October 10, 2020