title: Mechanisms for the keystone status of kangaroo rats: graminivory rather than granivory?
abstract: Graminivory by kangaroo rats (Dipodomys spp.) was investigated as a potential mechanism for the keystone role of these rodents in the dynamics of desert grasslands. Experiments confirmed that Ord's kangaroo rats (Dipodomys ordii) cut and consumed a large proportion of the tillers of three Chihuahuan Desert tussock-forming grass species. Field observations indicated that the characteristically cut grass tillers were absent from all-rodent and medium-sized kangaroo rat exclosures, but were frequent in large-sized kangaroo rat and rabbit exclosures, indicating that the medium-sized kangaroo rats (D. ordii, D. merriami) were responsible for grass cutting. Tiller waste as a percentage of peak standing crop ranged from 7% in grassland habitats to 0.7% in Flourensia cernua shrubland. Of the 13 species of perennial, tussock-forming grasses measured, only one, Muhlenbergia porteri, had no tillers cut by kangaroo rats. This study demonstrates that the keystone role of kangaroo rats in Chihuahuan Desert grassland ecosystems is probably the result of their graminivory.
authors.affiliation: Terrestrial Ecology Research Unit, Department of Zoology, University of Port Elizabeth, PO Box 1600, Port Elizabeth 6000, South Africa e-mail: zlagik@zoo.upe.ac.za; Fax: +27-41-504 2317, , , , , , ZA.
authors.forename: Graham I H
authors.initials: GI
authors.lastname: Kerley
authors.affiliation: U.S. Environmental Protection Agency, National Exposure Research Laboratory, Characterization Research Division, P O Box 93478, Las Vegas, NV 89196, USA, , , , , , US.
authors.forename: Walter G
authors.initials: WG
authors.lastname: Whitford
authors.affiliation: USDA/ARS Jornada Experimental Range, Dept. 3JER, New Mexico State University, Las Cruces, NM 88003, USA , , , , , , MX.
authors.forename: Fenton R
authors.initials: FR
authors.lastname: Kay
keywords: Chihuahuan Desert; Dipodomys; Grass populations; Key words Graminivory; Keystone species