Gambelia Sila Research Articles

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

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.

Sexual Dimorphism as It Relates to Natural History of Leopard Lizards (Crotaphytidae: Gambelia)

Sexual dimorphism is a phenomenon that occurs in a variety of animal taxa, and its occurrence can reflect and/or influence crucial aspects of the natural history of organisms. We examined the external morphology of three lizard species, Gambelia sila, G. wislizenii, and G. copei. Gambelia sila shows the prevalent sexually dimorphic condition among iguanian lizards of males attaining a larger head relative to body size (snout-vent length) and larger overall body size than females, whereas in G. wislizenii and G. copei, females attain a larger body size than males. We performed a detailed morphometric examination of these three taxa to (1) characterize interspecific differences in sexual dimorphism among these three closely related lizards, (2) test the hypothesis that sexual dimorphism in cranial shape exists in G. wislizenii and G. copei, and (3) examine intersexual body size and cranial shape variation among G. wislizenii populations inhabiting major North American geophysical regions. Morphometric analyses support the results of previous studies. Cranial shape dimorphism is present in some G. wislizenii populations, particularly those of the Great Basin, and in G. copei. Interregional comparisons reveal that G. wislizenii populations vary both in the degree of intersexual body and head size differences as well as in cranial shape dimorphism. Among regional groups, body and head size and cranial shape dimorphism exhibit an inverse relationship. These patterns of morphological variation are correlated with aspects of the ecology, behavior, and phylogenetic history of these taxa.

Microhabitat Use and Home Range Characteristics of Blunt-Nosed Leopard Lizards

We used radiotelemetry to determine habitat use and home range characteristics of 16 blunt- nosed leopard lizards (Gambelia sila) at two sites on the Naval Petroleum Reserves in California. Space use parameters of eight lizards occupying an area of relatively dense vegetation in 1982 and eight lizards inhabiting a sparsely vegetated site in 1984 were compared. Home range size, core area size, and amount of overlap of ranges did not differ significantly between sites. The difference in average home range size between males (4.24 ha) and females (2.02 ha) was borderline significant (P = 0.054). Female home ranges and core areas were overlapped extensively by male ranges (x = 79.8% and 50.3%, respectively). There was no evidence of intrasexual overlap of core areas. Male home ranges overlapped the ranges of up to four other males but female ranges did not overlap one another. At the more densely vegetated site, leopard lizards used washes significantly more than grassland, floodplain, and road habitats and they used grassland significantly less than other habitats. At the sparsely vegetated site, grassland was used more than wash habitat and hills were used less than all other habitats. Our data indicate that leopard lizard activity is concentrated in washes and other open areas when herbaceous cover is dense, but they are capable of utilizing the more extensive grassland habitat if vegetation is sufficiently sparse. Creating open space within the grassland habitat may have important management implications for this species in some areas.

Food-Item Use by Coyotes at the Naval Petroleum Reserves in California

Coyote (Canis latrans) food habits have been extensively documented (Bekoff, 1977). Use of food items by coyotes varies with location and time in response to spatial and temporal variation in food availability. Thus, siteand time-specific investigations are necessary to accurately describe local coyote foraging patterns. Relatively few investigations of coyote food habits have been conducted in California (e.g., Ferrel et al., 1953), and none were specific to the San Joaquin Valley. Additionally, coyotes in the southern San Joaquin Valley are sympatric with the endangered San Joaquin kit fox (Vulpes macrotis mutica = V. velox macrotis, cf. Dragoo et al., 1990) and potentially compete with foxes for food resources. Also, several other federally listed and candidate species occur in the southern San Joaquin Valley and may be preyed upon by coyotes. These species include the endangered giant kangaroo rat (Dipodomys ingens) and the blunt-nosed leopard lizard (Gambelia silus), and candidate species shortnosed kangaroo rat (Dipodomys nitratoides) and San Joaquin antelope squirrel (Ammospermophilus nelsoni). We investigated food-item use by coyotes at the Naval Petroleum Reserves in California (NPRC) to (1) determine annual and seasonal item use, and in particular to evaluate the dietary importance of leporids which are important prey for kit foxes (O'Farrell et al., 1987; J. H. Scrivner et al., in litt.), (2) assess the effect of annual leporid abundance on coyote food habits, and (3) determine whether coyotes prey on giant kangaroo rats, blunt-nosed leopard lizards, shortnosed kangaroo rats, and San Joaquin antelope squirrels. NPRC is an area of active petroleum production located 42 km SW of Bakersfield in western

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

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