Banner-tailed Kangaroo Rats and Shrub Invasion in Desert Grasslands

Proposal Abstract

This project contributed significantly toward our long-term research goal of understanding the role of kangaroo rats (Dipodomys spp.) in general, and banner-tailed kangaroo rats in particular (Dipodomys spectabilis) in the functioning of desert grassland ecosystems. Banner-tailed kangaroo rats (Dipodomys spectabilis) are mound-building heteromyid rodents of desert grasslands in the southwestern United States and northern Mexico. Each mound contains a complex burrow system, including caches of vegetative material, and is occupied by a single individual. Mounds differ from their surroundings in their vegetation, soil nutrient content, hydrologic properties, and soil fungi. Although both active and abandoned mounds may have shrubs (e.g., mesquite, Prosopis glandulosa; ephedra, Ephedra trifurca; creosote bush; Larrea tridentata) growing on them, active mounds tend to be kept free of vegetation by the activities of the kangaroo rat.

Previous research, including our own work, has shown that kangaroo rat mounds can profoundly influence local vegetation. We propose a conceptual model of the role of banner-tailed kangaroo rat mounds in shrub invasion of desert grasslands, in which kangaroo rat mounds play a role analogous to that of tree-fall gaps in "patch-dynamics" models of forest ecosystems. In this project, we have found the following:

1. Just as banner-tailed kangaroo rats can profoundly influence local vegetation, local vegetation itself has a profound influence on banner-tailed kangaroo rat foraging behavior, and presumably foraging success as well, leading to local variation in habitat quality. The presence of mesquite contributes significantly to reduced habitat quality for D. spectabilis.
2. Our initial study design involved a test of the hypothesis that feeding preferences of D. spectabilis imply possible mechanisms for their profound effects on local vegetation, retarding the process of shrub encroachment. The test of this hypothesis is underway, pending the completion of Jennifer Graves' masters' thesis. We expect to find that mesquite seedlings are a highly valued food item for D. spectabilis.
3. Our initial study design involved a test of hypotheses concerning the relation between mesquite establishment and active vs. abandoned D. spectabilis mounds. The test of this hypothesis is under way; its completion depends on the collection of additional data by Jennifer Graves for her masters' thesis. However, these data will be available only if summer precipitation on the study area permits collection of adequate vegetation data.

These findings have helped clarify the role of D. spectabilis in desert grassland ecosystems, and have helped us refine our conceptual model. They have also suggested numerous additional hypotheses to be tested and pursued in further studies. In addition, these findings have contributed to overall knowledge of the process of conversion of desert grasslands to shrublands, thereby contributing to sustainable management of desert grassland ecosystems.

Outcome

Article in Journal

Chalcraft, C.E., M.C. Andersen, F.R. Kay and B.P. Kotler. "Giving up densities as indicators of habitat quality for heteromyids in a Chihuahuan desert grassland/shrubland transition." Journal of Mammalogy (submitted).

M.S. Theses

Graves, J. 2002. Kangaroo rat (Dipodomys spectabilis): Effects on mesquite (Prosopis glandulosa) invasion and establishment." M.S. Thesis. New Mexico State University. Las Cruces NM.

Hernandez, C. 2000. Foraging ecology of banner-tailed kangaroo rats and desert grassland ecosystems. M.S. Thesis. New Mexico State University. Las Cruces NM.

Presentations

Graves, J.A., M.C. Andersen and F.R. Kay. 2001. "Effects of banner-tailed kangaroo rats on the invasion and establishment of honey mesquite in the Chihuahuan Desert." Poster, 8th annual meeting of the wildlife society. Reno NV.

Andersen, M.C. 1999. "Banner-tailed kangaroo rats and shrub invasion in desert grasslands." Presented, International Arid Lands Consortium's land management workshop: A tenth anniversary celebration of USFS, CSREES, Israeli and IALC Partnerships, November. Reno NV.

Funding