Diet of the Mogollon Vole as Indicated by Stable-Isotope Analysis (δ13C and δ15N)

Abstract

There are no published studies on the diet of Mogollon voles (Microtus mogollonensis) although this species occurs throughout the Southwest in montane forestlands. Mogollon voles are believed to be herbivorous, selecting the vegetative portion of grass as their dominant food source. Herbivores frequently select more easily digested C3 plants over C4 plants; we thus expected Mogollon voles would feed primarily on C3 plants. We collected hair samples from Mogollon voles captured in northern Arizona between 1967 and 2003 and plant samples from some capture sites. Then we compared stable carbon (δ13C) and nitrogen (δ15N) isotope ratios to investigate dietary preferences for C3 or C4 plants. Mean isotope ratios for C3 plants we sampled were −26.84‰ (s = 0.17) for δ13C and −0.02‰ (s = 0.32) for δ15N. For C4 plants, mean isotope ratios for δ13C and δ15N were −15.04 ‰ (s = 0.38) and −0.74‰ (s = 0.55), respectively. Mogollon voles were largely herbivorous based on δ15N (mean and standard error: 3.77 ± 0.17‰) and used C3 plants more than C4 based on δ13C C (−24.21 ± 0.14‰). Activities that lead to changes in plant species composition or reduction in C3 plants in montane grasslands and forests (e.g., excessive ungulate grazing) may reduce habitat quality for Mogollon voles.