Lizard Home Ranges: Methodology and Functions

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An evaluation of the methods for determining home ranges was made, and the factors affecting home range estimates were examined. Inadequate sample size and the use of statistically based models to correct for small sample size were the most common deficiencies in home range studies. The determinant and recapture radii methods unrealistically inflated home range estimates. The assumption of normality was not confirmed by actual data. The convex polygon method is the most attractive home range measurement to field biologists because it accurately describes the area used (if based on an adequate number of sightings), and it is simple, using only the actual sightings of an animal. By examining the relationship between number of sightings and cumulative home range size, the minimum number of sightings that accurately estimates home range can be empirically determined. Additionally, these data can provide information on the use of home ranges and territories. The time interval on which home ranges are based affect size estimates greatly. Many sightings per animal and short time intervals between censuses are necessary for accurate home range estimates. Eighteen was the minimum number of sightings to accurately measure home range size in Sceloporus virgatus. Eighteen is much larger than the minimum number commonly considered adequate. Few generalizations concerning home ranges are possible from the published data on North American iguanid lizards. The data indicate that caution is necessary in interpreting the function of home ranges from correlative data, and that the same data can support alternative hypotheses regarding function. Many researchers studying lizard populations have calculated home range size. A home range is the entire area within which an individual moves. Food, retreats, and mates are found in this area. Home range data can answer many interesting questions in ecology and behavior assuming accurate measurements of home ranges are available. In reviewing the literature on North American iguanid lizards, I found that the methodology varies so greatly between studies that the comparative value of the data is limited. Estimates of home range size for the same data vary four fold depending on the method used. This article critically evaluates the methodology commonly used in home range studies of lizards with the goal of increasing the rigorousness and reliability of home range estimates. Data from my study of Sceloporus virgatus (Rose, 1981) demonstrates the usefulness of the suggested procedures. Results from many researchers are required to make generalizations on the importance of variation in home range size, and standardized procedures are necessary to faciliate comparisons between studies. Variation in home range size is expected between species, habitats, and years. Much research is currently devoted to explain this variation. Specifically, most home range studies deal with the relationship between: 1) a lizard's social organization and its use of space; 2) home range size and function; 3) home range size, productivity of the environment, and population density; and 4) home range size, mating success, and survival.