Understanding the spacing patterns of individuals in a population of animals is important for establishing the specific functions of territorial behavior. Here, we couple a comprehensive analysis of home range with demographic information and focal behavioral observations of Sceloporus undulatus (eastern fence lizard) to investigate (1) spacing patterns, (2) the determinants of home range, and (3) the functional significance of territorial behavior and traits related to territorial behavior (body size, color). Male home-range area is an order of magnitude larger in the New Jersey population of S. undulatus described here than in other populations, whereas female home ranges are comparable in area to other populations of this species. Home-range area is positively correlated with body size in adult males, although this relationship is not found within age classes, and males share about 50% of their home range with other males. After removal of the effect of body size, residual home-range area is smaller in two-year olds (first breeding season) than in older males. Home-range area increases as a function of the number of overlapped females, even after the effect of body size is statistically removed, and the sightings of males within their home ranges are tightly clustered in and near the home ranges of females. Males courted females in 60% of focal behavioral observations and contested other males in 14%, always in close proximity to a female. Relative body size, color, and behavior were displayed by contest “winners” and “losers” in the same manner as previously characterized in captive lizards. Of the three status traits examined, only body size explained variation in home-range area, apparently reflecting the ability of males to court increasing numbers of females as they get older and larger. The winners of contests gained access to the nearby female, but contests had no lasting influence on the locations where males subsequently were sighted. Thus, the size and shape of male home ranges are determined largely by the number and locations of females with whom males interact. Females themselves and not specific sites or home-range area are the contested resources. Plasma corticosterone was correlated with the area of a male's home range overlapped by female home ranges. Because this measure of overlap may reflect the frequency of interactions between lizards and assuming that elevated corticosterone reflects a stress response, social interactions including contests between males and courtship of females appear to be stressful in free-living male S. undulatus.

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