Establishing the social system of a population is key to studying the evolution of behaviors. However, observations of social interactions needed to infer social systems are difficult to obtain for many species. An alternative way of understanding social systems is by studying the space-use pattern of individuals. Along with ecological factors, space use is largely governed by interactions among individuals: typically, competing individuals avoid each other, and individuals benefitting from each other share space. We investigated the social system, specifically the mating system, and the nature of intrasexual interactions between adults, by quantifying space-use patterns of individuals over their adult lifespan in the tropical Psammophilus dorsalis lizard. Males had substantially larger home ranges than females during the mating season, but not during the nonmating season. Female home ranges were small, and showed minimal overlap with other females throughout their lifespan, suggesting consistent intrasexual competition among females. In contrast, males showed minimal overlap with other males in the nonmating season but increased overlap in the mating season, suggesting that males resolve intrasexual competition through other means, like contests, during the mating season. Patterns of overlap between male and female home ranges in the mating season indicated a socially polygynous mating system. Our study provides an initial understanding of home-range patterns and associated inferences of within- and between-sex interactions across the lifespan of a tropical lizard, Psammophilus dorsalis. It highlights the insights into the social structure of a population gained from dispersion patterns of individuals.