Exhibits

The Stephens' kangaroo rat (Dipodomys stephensi, Family Heteromyidac) is an endangered desert rodent of southern California. The historic range of D. stephensi has been severely reduced by urban and agricultural development, and remaining habitat is considerably fragmented. We estimated the minimum viable population size of D. stephensi from a demographic model that incorporated information about survivorship and fecundity in relation to stochastic variation in rainfall. According to the model, a population of 13,210 individuals has a 95% probability of persisting for 100 years. At a density of 10 individuals/ha, this value corresponds to a reserve size of 1321 ha. Based on this estimate and maps of current distribution, land use, and soil type, we suggested nine potential reserve sites and recommended that at least three reserves be established to secure persistence.

An ecosystem approach focuses on landscapelevel processes (natural and human) that support or affect the area, such as this wetland, as a means of conserving the species within i t (Wetland in Lower Iron River, a tributary to Lake Superior. Photo by Joan Elias.)-1 Endangered Species UPDATE Vol. I 0 Nos. 3 & 4 1993 Thinking "Ecosystems" is Learned Several of the authors remind us of the extraordinary expense in speciesby-species approaches, and offer this as Judy Tasseis the Editor of the EhgeredSpccies UPDATE. She is a Ph.D. student in the School of Natural Resources and Environment at the University of Michigan, studying mechanisms for wildlife reintroductions and movements of individuals in small release populations.

The Stephens' kangaroo rat (Dipodomys stephensi, Family Heteromyidae) is an endangered desert rodent of southern California. The historic range of D. stephensi has been severely reduced by urban and agricultural development, and remaining habitat is considerably fragmented. We estimated the minimum viable population size of D. stephensi from a demographic model that incorporated information about survivorship and fecundity in relation to stochastic variation in rainfall. According to the model, a population of 13,210 individuals has a 95% probability of persisting for 100 years. At a density of 10 individuals/ha, this value corresponds to a reserve size of 1321 ha. Based on this estimate and maps of current distribution, land use, and soil type, we suggested nine potential reserve sites and recommended that at least three reserves be established to secure persistence. Common name California orcutt grass Munz's onion Payson's jewelflower Many-stemmed dudleya Palmer's grapplinghook Thread-leaf brodiaea San Diego button celery Engelmann oak Little mouse-tail bat San Diego horned lizard Orange-throated whiptail lizard Cooper's hawk Golden eagle Bald eagle Long-eared owl California gnatcatcher Coastal cactus wren Yellow-breasted chat Orcnttia californica Allium fimbriatum, var. munzii Caulanthus simulans Dudleya multicaulis Harpagonella palmer, var. palmer Brodiaea filifolia Erynigium aristulatum, var. parishii Quercus engelmannii Myosurus minimus Phrynosoma coronatum blainvillei Cnemidophorus hyperythrus Accipiter cooperii Aquila chrysaetos Haliaeetus leucocephalus Asia otus Polioptila californica Campylorhynchus brunneicapillus sandiegense Icteria virens

The maternal and paternal behavior of Kerodon rupestris was examined. Quantitative differences between fathers and mothers and between mothers raising young with fathers present and with fathers absent were assessed. Growth rates of young raised by paired females and by lone females were compared. The male provides direct paternal care to the young by engaging in allogrooming, sniffing, and huddling. There is no significant difference between the sexes in the amount of contact promoting behavior given to the offspring, nor are the sexes significantly different in the amount of exploratory sniffing of the offspring. When the male is absent, the female spends a greater amount of time in contact with the young. Young raised by lone females gained significantly more weight than young raised by paired females. The suggestion that indirect paternal care acts to reduce female aggression to the young and relieve the energy expenditure burden of the female is discussed. The results indicate that social experience is gained at the expense of physical nurturing when the male is present.