Biology ETDs

Publication Date

Fall 12-7-2017


In the Northern Chihuahuan desert, grassland and shrubland co-occur as separate stable states under similar climatic conditions. In this bottom up (resource driven) system, the magnitude and timing of precipitation events drives primary production which varies from year to year and season to season. Climate change is predicted to alter precipitation regimes, and increase aridity, facilitating shrub encroachment which results in increased landscape heterogeneity and a decrease in plant biodiversity. These changes will likely result in a restructuring of small mammal communities.

We used long-term data on precipitation, primary production, and abundances of small mammals in adjacent grassland and shrubland stable states and across an ecotone between grassland and shrubland to characterize foraging patterns in heteromyids, food-caching granivores, and cricetids, omnivores that do not cache and rely on body fat for short term energy reserves. To accomplish this, we trapped 7,063 mice across a grassland/shrubland ecotone which resulted in 3,560 mouse plasma isotope analyses from 1,533 individually marked mice. By comparing raw isotopic values of d13C and d15N in mouse plasma to plant values, we can track community wide foraging patterns. Using a subset of 1,406 plasma samples from one species (Perognathus flavus) we were able to document the development of individualized foraging strategies to alleviate intra-specific competition during a population explosion.

The grassland supports a lower density subset of rodent species found in shrubland. Using a 25 year small mammal trapping dataset, there was no indication of directional change in species composition in either stable state, just a temporal reordering of species dominance. Consumer diets track nitrogen on the landscape, with cricetids foraging at a higher trophic level than heteromyids during resource abundance, diets converge and broaden as resources decline. A population boom in Perognathus flavus increased intraspecific competition causing some individuals to specialize on either C3 or C4 resources, while 60% of the population remained generalist foragers. Mice in this community exhibit a high degree of dietary plasticity to survive high stochasticity in resource quantity and quality. This study uses a unique suite of tools to examine the interface of precipitation, primary production, and small mammal foraging characteristics.

Project Sponsors

Dr. Scott Collins, Dr. Seth Newsome, Dr. Blair Wolf, Dr. Anthony Joern




Community Dynamics, Small Mammals, Foraging Strategies

Document Type


Degree Name


Level of Degree


Department Name

UNM Biology Department

First Committee Member (Chair)

Scott Collins

Second Committee Member

Seth Newsome

Third Committee Member

Blair Wolf

Fourth Committee Member

Anthony Joern

Included in

Biology Commons