Endangered Species Recovery Program

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

Presented To Joint Meeting of

Society for Conservation Biology and the Ecological Society of America
Providence, RI
August 1996

by

Ellen A. Cypher
and
Daniel F. Williams

Abstract

Many species in California's San Joaquin Valley are in danger of extinction from habitat loss, including giant kangaroo rats (Dipodomys ingens) and the annual plants California jewelflower (Caulanthus californicus) and San Joaquin woolly-threads (Lembertia congdonii). All 3 species are federally listed as endangered and occur on the Carrizo Plain Natural Area in San Luis Obispo County, California. During the growing seasons of 1993-1995, we compared attributes of plants growing on giant kangaroo rat precincts (burrow systems) to those in interspaces (between precincts) to determine if activities of the animals benefit California jewelflower and San Joaquin woolly-threads. California jewelflower occurred on precincts with greater frequency than expected, but San Joaquin woolly-threads did not follow a predictable distribution pattern with respect to precincts. Plants of both species typically matured earlier on precincts than in interspaces. The proportion of seedlings surviving to reproduction did not differ between precincts and interspaces for either species. Reproductive output of both plant species on precincts equaled or exceeded that in interspaces. Giant kangaroo rat activities modify soil characteristics on precincts and provide favorable sites for the growth of California jewelflower and San Joaquin woolly-threads.