Occurrence and Potential Interspecific Interaction of Two Species of Chipmunks (Tamias) in Rocky Mountain National Park
Sholty, Kathleen E.
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Two species of chipmunks, Tamias minimus and T. umbrinus, are known to occur in the Front Range of the Colorado Rockies, inhabiting a variety of vegetation types and specific elevational ranges. These two species are often difficult to discern and identify difficult due to the similar morphological characteristics they display, as well as their sympatric distributions. Characterizing the interactions between overlapping populations may also be problematic. Our study was part of a larger survey of small mammal diversity in Rocky Mountain National Park (RMNP), Colorado from which we chose to focus on the distribution and interactions between T. minimus and T. umbrinus. We surveyed chipmunks along an elevational gradient within a variety of vegetation classes using both live traps and snap traps and recorded various morphological measurements. We also examined the potential for character displacement as a result of interspecific competition and analyzed body mass of T. umbrinus in the presence and absence of T. minimus. We performed Discriminant Function Analysis (OF A) to determine the accuracy of our identifications in the field. Tamias minimus had an expectedly wider range in both elevation and vegetation than T. umbrinus. Both species frequented the same area in 4 out of 7 sites, at middle to higher elevations, within the Lodgepole Pine and Sub-Alpine forests. Independent samples t-test conflrmed no significant difference between the body mass of T. umbrinus in the presence and absence of T. minimus, suggesting no implication of morphological divergence taking place as a result of competition. The results from our survey provide support for future studies concerning distribution and interactions, including possible exclusion, among chipmunk species in and around RMNP.