VARIATION IN INDIVIDUAL GROWTH IN THE TREE LIZARD, UROSAURUS-ORNATUS - EFFECTS OF FOOD AND DENSITY

The influence of density and food availability on indivdual growth rates of tree lizards, Urosaurus ornatus, from southwestern New Mexico was investigated using a density manipulation. The density of an experimental population was reduced by one-third relative to its premanipulation density. Before the manipulation both populations had similar mean individual growth rates; however, after the manipulation, the mean individual growth rate of tree lizards in the experimentally reduced population was twice the mean individual growth rates for tree lizards in the control population. Annual variation in food abundance also influenced individual growth rates, with slowest growth in the year of least food availability. Intraspecific density and food abundance both appear to affect individual growth rates in these populations, but their importance may vary annually.