- Empirical data on behavior, such as space-use patterns, are important to the success of animal re- introductions. We studied space-use patterns in a growing population of Asiatic wild ass ( Equus hemionus ) reintroduced into the Ramon erosion cirque in the Negev desert, Israel. Between 1988 and 1995 we used di- rect observation to determine the location and association of males and females. All adult females and dom- inant males were individually recognized. Home ranges of dominant males overlapped little, suggesting that in this population males are territorial. After the first release of males and females into the wild, only one ter- ritory was established, and it covered most of the 20,000 ha of the cirque. After 6 years the number of male territories increased as the number of males in the population increased, and average territory size de- creased. Male territories were near permanent and ephemeral water sources, but the water sources were at the peripheries of the territories and were not centers of activity. When there was only one territorial male, fe- male home ranges were almost entirely within the territory. As male territory size decreased, so did the spa- tial association of females with a single male. During the breeding season, males spent more time in close as- sociation with female groups, adopting what may temporarily appear to be a harem breeding strategy. Although demographic and environmental factors pose a greater threat to small populations, our data sup- port the hypothesis that in small, reintroduced populations of territorial, polygynous species, effective popula- tion size ( N e ) may be dangerously small. Our data suggest that this situation may last for several years until new males are recruited into the population. Thereafter, rapid male turnover and female use of several male territories may ameliorate this problem. We found no relationship between male turnover rate and female reproductive success. The establishment of more male territories is key to increasing N e and should be the ba- sis for planning reserves for territorial, polygynous species.