The ecology of a population of Xantusia vigilis, the desert night lizard. American Museum novitates ; no. 2247

Supplemental Materials
Journal Title
Journal ISSN
Volume Title
New York, N.Y. : American Museum of Natural History
"Over a period of seven years we studied a population of desert night lizards, Xantusia vigilis, in the Antelope Valley part of the Mohave Desert in southern California. These secretive lizards inhabit decaying stumps and fallen trunks and limbs of Joshua trees (Yucca brevifolia), nests of wood rats (Neotoma), and similar surface litter. On visits to the study area during the winter, seven times in December and once in March, when the lizards aggregate and are relatively easy to collect in large numbers, we captured 656 lizards and marked them by clipping toes before releasing them. We recaptured 152 marked lizards a total of 216 times. General observations made during the field surveys, together with data on growth, longevity, and movements derived from the recaptured individuals, form the basis for this report. Xantusia vigilis is viviparous and produces only one to three young, usually two, in a litter... Little growth takes place before the winter period of relative inactivity... At the end of slightly more than three years of life the average length is 38.4 mm., range 36-41 mm. Growth rate has decreased considerably, and there is considerable overlap in sizes of individuals comprising samples of two-year-old and three-year-old lizards. The growth rates of male and female lizards evidently diverge in or before the fourth year of life... The amount of growth, particularly in the early years of life, appears to be correlated directly with rainfall which presumably determines the abundance of food. The majority of Xantusia that survive to adulthood lose the tail at least once... Suitable habitat is discontinuously distributed; lizards seldom leave the shelter of their logs or rat nests and take up residence elsewhere... We estimate that an average of 518 lizards (range, 302 to 680) inhabited the 27-acre study area during the period of our winter surveys- about 19 per acre or 12,000 per square mile. These figures are crude approximations and undoubtedly err on the low side. A large percentage of the population, about 50 per cent on the average, is composed of adult lizards- males two years or more in age, females three years or more. In unusually dry years many and perhaps most of the female lizards produce no young, presumably because of inadequate nutrition stemming from a scarcity of the invertebrates upon which the lizards feed... As might be anticipated for a species in which the females do not mature until three years of age and produce only two young per year, Xantusia vigilis has a long average life span. The average life expectancy at birth may be as high as four years, and individuals live for at least nine years, probably longer. Predation is thought not to be significant in population control. Social antagonism causes territorial deployments within the populations during the spring and hot summer months. If shelter is inadequate, heat and antagonism may act together in density-dependent fashion as limiting factors. Unusually cold weather in the winter may find some lizards insufficiently sheltered, though at this season most individuals aggregate in favorable sites. In comparison with other lizards, Xantusia vigilis shows a high life expectancy at birth, slow growth, late maturity, and low reproductive potential- perhaps the lowest known among lizards"--P. 51-53.
57 p. : ill., map ; 24 cm.
Includes bibliographical references (p. 53-57).