Biology ETDs

Publication Date



The relatively pristine upper Gila River in New Mexico is a stronghold for endemic native fishes despite the presence of non-native fishes. In other, more severely human-impacted tributaries in the Colorado River basin, non-native fishes are a major factor in native species decline and extirpation. I tested whether presumed negative effects of non-natives on natives are compounded during drought using an approach based on Stable Isotope Analysis (SIA) and comparisons of resource use overlap during different flow conditions. Fish specimens were selected from natural history collections to represent a time series that encompassed wet and dry years, as well as varying non-native abundances. I estimated 'isotopic niche space' by plotting δ13C vs. δ15N for native and non-native fishes and statistically compared breadth and overlap in niches among species. I hypothesized that during low-flow periods, the availability of resources is constrained, causing isotopic niches of non-natives and natives to overlap more, which increases the potential for competition. I hypothesized that during wet periods, resource space is broader, suggesting reduced overlap of resource use. My results indicate that low-flow conditions constrain resources in isotopic space, and wet conditions increase diversity of available resources. During wet conditions, native and non-native groups have more varied resource use. SIA of museum specimens offered the potential to test key hypotheses about the impact of non-native species on a native fauna, and provided understanding of the environmental context that non-native species negatively impact native fishes. Such understanding is important for conservation of the fishes of the Gila River, where climate change and pending water diversion could lead to further imperilment of native fish abundance.

Project Sponsors

Graduate Program Student Association, UNM The Nature Conservancy Biology Graduate Student Association, UNM The Center for Stable Isotopes, UNM




Invasion ecology, Native fish conservation, Arid land rivers

Document Type


Degree Name


Level of Degree


Department Name

UNM Biology Department

First Committee Member (Chair)

Gido, Keith

Second Committee Member

Stone, Mark

Third Committee Member

Propst, David