Diversity, distributions, and evolution of Rocky Mountain and Andean stream insects

Abstract

Concordant with latitudinal increases in seasonality, the "climate variability hypothesis" (CVH) posits that the breadth of species' thermal tolerances should increase with latitude. Across elevations, the "mountain passes are higher in the tropics hypothesis" (MPHT) postulates that the narrow thermal tolerances of tropical species should limit their dispersal across elevations more than the broad thermal tolerances of temperate species. We consequently expect tropical species to have more limited elevational ranges and higher rates of population isolation, divergence, and speciation than temperate species, which could lead to higher tropical than temperate species richness. Moreover, many tropical species might be cryptic, as they have diverged primarily in physiological and dispersal traits, rather than traits with distinct morphological phenotypes. In this dissertation, I investigate how the CVH might provide a mechanistic explanation for global trends in species richness, cryptic diversity, and elevational distributions. In chapter one, I recapitulate the CVH and MPHT hypothesis and summarize related key literature. In chapter two, I characterize the diversity and distributions of stream insects in the Colorado Rocky Mountains. In chapter three, I compare the species richness and elevational ranges of species from the Colorado Rocky Mountains and the Andes of Ecuador. Lastly in chapter four, I integrate data from physiological, landscape genetic, and biogeographic investigations to evaluate the support for the CVH as a key mechanism determining global trends in species diversity, distributions, and vulnerability to climate change.