Factors Influencing the Distributions of Two Species of Perognathus

Abstract

Perognathus penicillatus and Perognathus intermedius were studied in two areas in Dona Ana County, New Mexico, from 1970—1972. Perognathus penicillatus was associated with sandy soils and P. intermedius with soils composed of predominantly larger particles. Soils from areas where P. intermedius was found had a lower heat buffereing capacity than soils from areas occupied by P. penicillatus. Artificial burrows when occupied by either species had a higher concentration of CO2 in P. intermedius type soils. Perognathus penicillatus occupied burrows in cooler places, survived a narrower temperature range, and exhibited higher rates of evaporative H2O loss with increased ambient temperature and CO2 concentration than did P. intermedius. Perognathus penicillatus was the more aggressive species, and dominated P. intermedius in laboratory encounters. Perognathus penicillatus can probably exclude P. intermedius from habitat that provides a burrow microclimate that the former can tolerate. Perognathus intermedius is physiologically able to survive in the more extreme habitat not suitable for P. penicillatus. The distribution of soil types and other microgeographical features that affect the burrow microenvironment, together with rainfall and temperature patterns, determine the areas where the two species will persist. The climatic variability of this desert site can result in changes in overall suitability of an area and hence in distribution and range of each species.