- Competitive exclusion is a key concept in ecology describing the exclusion of one species by another from access to a limited resource. Competitive interactions between chipmunk species in the Great Basin, documented by James Brown in 1970, are often used as a textbook example of competitive exclusion. Whether competitive interactions and resource partitioning among the Cliff Chipmunk (Tamias dorsalis), the Uinta Chipmunk (T. umbrinus), and the Least Chipmunk (T. minimus) have remained stable across space and time is unknown. We addressed this question by analyzing δ13C and δ15N values in hair for these three chipmunks along elevation gradients within three mountain ranges in the Great Basin, the Ruby Mountains, Toiyabe Range, and Snake Range. These gradients represent historical resurveys, thus we also evaluated isotopic change within and across species over the last century. We found mixed results supporting partitioning among these species that varied across space but not time, despite changes in the resource base and climate. Furthermore, species have shifted in isotopic space towards more negative δ13C values (even after Suess correction) but maintained a fairly consistent range of δ15N values over the last century. We also found negative relationships between δ15N values and elevation for T. minimus in the Ruby Mountains and Snake Range.