Endangered Species Recovery Program

Influence of the endangered giant kangaroo rat
on the dispersion and fitness of two
endangered plant species

Presented To

Western Section of the Wildlife Society
Maui, HI
Feb. 1994

and

Elk Hills Endangered Species Program Review
Bakersfield, CA
1994

by

Ellen A. Cypher
and
Daniel F. Williams

Abstract

The effects of endangered giant kangaroo rat (Dipodomys ingens) activity on the distribution and fitness of the endangered, annual plants Caulanthus californicus and Lembertia congdonii were evaluated on the Carrizo and Elkhorn Plains, San Luis Obispo County, California. During Spring 1993, frequency of occurrence on D. ingens burrow systems (precincts) was determined for the endangered plants and for random points. Survival, size, and reproduction also were compared for plants growing on precincts and between precincts (in interspaces) in two populations of each species. Caulanthus californicus occurred more frequently on precincts than did random points, but L. congdonii occurred randomly with respect to precincts. In general, precincts were beneficial or neutral for growth of both plant species, but responses varied by population. At one site, survival was higher for Caulanthus californicus individuals on precincts, but growth and reproduction did not differ significantly between plants on precincts and those in interspaces at either site. Survival did not differ between L. congdonii individuals on precincts and those in interspaces. Size and reproduction did not differ between L. congdonii plants on precincts or in interspaces in the Carrizo Plain population but did differ significantly at the Elkhorn Plain site. Giant kangaroo rats may be important seed dispersal agents for C. californicus but not for L. congdonii. Furthermore, giant kangaroo rat precincts may promote fitness of these plant species in areas where resources are limiting.