Ecology of the Iguanid Lizard Callisaurus draconoides

Abstract

Various aspects of the life history of Callisaurus are described and discussed, including: movements, microhabitat, foraging behavior, diet, size, growth, age, population structure, reproduction, sexual dimorphism, sex ratio, abundance, thermoregulation, time of activity, tail loss and predation, and leg length. Callisaurus hatchlings emerge from mid-July through November and grow rapidly, with most individuals attaining minimum adult size at ages of less than a year. Mean distance between captures was 20.3 m in seven immatures and 31.9 m in six adults. Mean growth rate of nine first-year lizards was 6.5 mm per month. One or more clutches of two to eight eggs are laid annually (mean of 73 clutches: 4.42). Oviducal eggs, and presumably egg deposition as well, occur from early June through at least late August. Males have enlarged testes from April through mid-August on southern areas, whereas on northern areas testes are reduced in size during late July and August, suggesting a shorter breeding season in the north. Clutch size is not correlated with female snout-vent length or with any of several measures of precipitation. Estimates of abundance vary from about .02 to 1.75 lizards per hectare, but are not correlated with the percentage of open ground, or with any of several precipitation statistics. There are latitudinal shifts in diet and percentage of females with broken and regenerated tails, and it is likely that the available prey and the level of predation differ within the geographic range. The frequency of broken tails increases with size, perhaps reflecting increased numbers of contacts with predators as the lizards age. Both the forelegs and the hindlegs of Callisaurus, expressed as percentages of snout-vent length, are significantly longer than the same measurements on eight other species of North American desert iguanids. Hindleg length is correlated with the frequency of use of open spaces in North American flatland desert lizards. Various aspects of the ecology of Callisaurus are briefly compared with those of some related and/or ecologically similar species of lizards.