Daniel F. Williams

Population Ecology of Blunt-Nosed Leopard Lizards in High Elevation Foothill Habitat

Abstract We captured 1078 Blunt-Nosed Leopard Lizards (Gambelia sila) 2396 times between 1989 and 1994 on the Elkhorn Plain, San Luis Obispo County, California. Based on size at first capture, we caught 119 adult (≥90 mm snout–vent length [SVL]) and 430 hatchling/juvenile (<90 mm SVL) males, and 139 adult and 390 hatchling/juvenile females. Sex ratio of males to females was 1.04 (549 males/529 females). Adult G. sila generally became active in April, and activity remained relatively high into July. Hatchlings were first noted in either July or August and generally could be found until early November, except in 1990 when no hatchlings were found at any time. Mean number of adults and hatchlings found active each day differed significantly across years, but as many as 32 adults and 42 hatchlings were seen on a plot during a census. Estimates of population abundance on a plot also varied yearly from 20–164 adults and 0–273 hatchling/juveniles and seemed to be affected either by too little or too much rain. Differences in daily activity varied and were moderately well explained by environmental factors. We estimated survivorship of lizards and found 29.0% of hatchlings from 1992 survived to 1993, and 14.6% of hatchlings from 1993 survived to 1994. The oldest G. sila found was a female estimated to be 4 years, 10 months when last caught, although most adults were not seen after 2 yr. Growth of individuals varied by year: highest growth rates were for lizards that hatched in 1991 and 1992, and lowest growth occurred in lizards that hatched in 1989. We found adult leopard lizards with eggs in all years but 1990. Females generally were gravid by late April or early May, and some females were found with eggs in early July. Female size at first reproduction was about 90 mm SVL, clutch size ranged from 1–6 eggs, and overall mean clutch size regardless of year or clutch order was 3.4 eggs. Many females produced multiple clutches in a year, and we found up to four clutches by a single female.

Gene flow among San Joaquin kit fox populations in a severely changed ecosystem

AbstractThe San Joaquin kit fox (Vulpes macrotis mutica) was once ubiquitous throughout California’s San Joaquin Valley and its surrounds. However, most of its habitat has been lost to irrigated agriculture, urban development, and oil fields. The remaining foxes are concentrated in six areas, although there are several small pockets of foxes throughout the Valley. To help conserve kit foxes, we sought an ecological understanding of the level of genetic variation remaining in these locations and the extent of gene flow among them. We collected tissue from 317 kit foxes from 8 sites and estimated genetic variability in and gene flow among sites using data from 8 polymorphic, microsatellite markers. We found no differences in both observed and expected heterozygosity between locations using Bonferonni corrected paired t-tests. We found differences in mean number of alleles per locus, even after we used Monte Carlo simulations to adjust for sample size differences. Population subdivision was low among sites (Fst=0.043), yet a matrix of pairwise Fst values was correlated with a matrix of pairwise geographic distances. An assignment test classified only 45% of the individuals to the site where they were captured. Overall, these data suggest that kit fox dispersal between locations may still maintain genetic variation throughout most of the areas we sampled.

Effect of Drought on Blunt-Nosed Leopard Lizards (Gambelia sila)

We studied a population of blunt-nosed leopard lizard (Gambelia sila) on the Elkhorn Plain, California from 1988-1991. Sufficient precipitation fell during the winters of 1987-1988 and 1990-1991 to produce abundant herbaceous ground cover the following springs. Winter rains in 1988-1989 produced low amounts of ground cover, and rains in 1989-1990 did not cause any appreciable number of annual plants to germinate. Counts of grasshoppers differed significantly between 1990 and 1991, with 10-60 times more grasshoppers counted in 1991 than 1990. In 1988, 1989, and 1991, adult leopard lizards, together with yearlings that hatched the preceding year, emerged from winter torpor in the spring and remained active through June. A few adults remained active into August, and in 1991 into September. In these same years, hatchlings appeared aboveground in August, and stayed active into September or October. However, in 1990, only yearling lizards were found active aboveground, and no reproduction occurred. Adult Gambelia sila have the ability to remain belowground > 21 mo during periods of low prey abundance. One of the density-independent factors of the environment that can affect populations of lizards is drought. Periods of below-average rainfall will decrease growth of plants, particularly herbaceous annuals, which in turn can depress populations of arthropods. Blunt-nosed leopard lizards (Gambelia sila) are mainly insectivorous (Montanucci 1965; Tollestrup 1979; Kato et al. 1987). Years with below-average precipitation can directly affect this species by lowering abundance of its prey. Gambelia sila is listed as an endangered species throughout its range in the San Joaquin Valley of California, and approximately 15% of its habitat remains (Germano and Williams 1993a). Understanding the response of populations of G. sila to environmental fluctuations is necessary for planning its recovery. In this paper, we discuss the ecology of a population of G. sila during a period of drought. We monitored changes in activity and reproduction of this species over four years, and correlated these changes with variation in environmental conditions. We discuss our results in light of possible responses that a long-lived lizard could make to a variable environment.

USE OF AGRICULTURAL LANDS BY SAN JOAQUIN KIT FOXES

Abstract Although the current range of the endangered San Joaquin kit fox (Vulpes macrotis mutica) borders large areas of farmland, the ecology of this species rarely has been studied within an agricultural setting. In central California, we examined habitat use, prey availability, and diet of radio-collared kit foxes inhabiting an aqueduct right-of-way (ROW) bordered by farmland. During both years of study (1998–1999), nocturnal locations of foxes occurred more often than expected (based on habitat availability) in the ROW and less often than expected within annual crops. Orchards were used disproportionately more than their availability during 1998 and were used in proportion to availability during 1999. Kit foxes traveled up to 1.1 km into annual crops and up to 1.5 km into orchards. Among diurnal locations (den sites) of foxes, 98% were within the ROW. Live-trapping revealed higher densities and greater diversity of rodents along the ROW than within farmland. Remains of murid rodents were found in 79% of kit fox scats. Our findings indicated that kit foxes ranged into orchards and annual croplands at night, but almost never occupied these areas during the day. The lack of den sites and low prey availability within farmland probably limited the ability of kit foxes to exploit and occupy these areas. Providing artificial den sites within croplands (especially within orchards) and along canals may increase use of farmland by kit foxes and facilitate their movement between isolated patches of natural lands.

ONTOGENETIC AND SEASONAL CHANGES IN COLORATION OF THE BLUNT-NOSED LEOPARD LIZARD (GAMBELIA SILA)

Abstract Among crotaphytids, the blunt-nosed leopard lizard (Gambelia sila) is one of only 2 species known in which adults do not have permanent dichromatic patterns, but both males and females display bright breeding colors. Males in most populations develop a salmon color over most of their head and body, whereas females develop rusty red blotches laterally along the head and trunk. Also unusual is the yellow color exhibited by juveniles. Between 1992 and 1994, we captured adult and juvenile G. sila on the Elkhorn Plain, San Luis Obispo County, California, and scored individuals for their coloration. Juvenile G. sila developed a yellow color on the undersides of their hind limbs and tail that was apparent when they were about 55 mm snout-vent length (SVL) and was prominent until about 85 to 90 mm SVL. Both males and females developed breeding colors between 85 and 95 mm SVL. Breeding colors of adults developed soon after they emerged each year in April or early May, and most adults retained breeding colors until they ended activity in July or August, although coloration fluctuated within a season for some individuals. Individual differences in the amount of coloration occurred with some large adults never developing fully bright breeding colors. Females produced multiple clutches in each year, and their breeding colors were not immediately apparent with their first clutch and sometimes faded, but did not disappear, between clutches.

Home range size and habitat selection of reintroduced Sylvilagus bachmani riparius

Abstract Effective restoration of threatened or endangered species requires understanding of basic ecological requirements such as habitat selection and home range needs. The endangered riparian brush rabbit (Sylvilagus bachmani riparius) occupies areas of dense, brushy cover along streamside communities in the San Joaquin Valley of California, but over 93% of this habitat has been lost to urban and agricultural development. We released over 325 captive-born rabbits at the San Joaquin River National Wildlife Refuge (Refuge) between July 2002 and July 2005, and we monitored 312 of these rabbits via radiotelemetry to assess spatial and habitat selection. Home ranges and core areas were similar among males and females, and were larger in the breeding season than during the nonbreeding season. Perhaps reflecting a growing population, home range estimates decreased in size over the duration of the study. Animals moved in response to a wildfire in July 2004, but home range area was similar in 90-day pre- and postfire periods. Of 1,143 possible dyads, 534 (47%) exhibited a mean of 86% overlap in 95% fixed-kernel home ranges. Overlap did not differ by dyad type (e.g., male–male), but was greater in nonbreeding than in breeding seasons; unlike home ranges, we did not detect any temporal changes in overlap as might be expected in a growing population. Riparian brush rabbits exhibit scale-independent habitat selection, disproportionately favoring thick understory cover such as sandbar willow mixed with dense shrubs (blackberry, roses). Refuge managers have promoted escape cover and flood refugia at strategic locations throughout the Refuge; our results concur that these are important habitat elements in the niche of riparian brush rabbits.

Use of Simulation Modeling to Evaluate Management Strategies for Reintroduced Riparian Brush Rabbits in California

Abstract The riparian brush rabbit Sylvilagus bachmani riparius is restricted to areas of dense cover along rivers and tributaries in the Central Valley of California, USA, and is considered endangered under the U.S. Endangered Species Act. An approved recovery plan for this subspecies recommended establishment of three additional self-sustaining populations within its historical range. Concurrent with habitat restoration efforts that included revegetation of levees and provision of flood refugia, we reintroduced 325 captive-bred individuals to the San Joaquin River National Wildlife Refuge between July 2002 and July 2005, and monitored their survival with radiotelemetry. Using available survival estimates and estimated reproductive parameters, we developed a population viability analysis model to determine the risk of extinction of the reintroduced population under a series of alternate scenarios including different release strategies. All model scenarios resulted in high probabilities of extinction over...