This is a two.year collaborative project between two American principal investigators .. Andrew T. Smith of Arizona State University and F. Stephen Dobson of Auburn University .. and Wang Xuegao of the Northwest Plateau Institute of Biology, Chinese Academy of Sciences. This institute is located in the city of Xining in the Qinghai.Xizang (Tibetan) Plateau. Direct observation of the number of offspring produced in a lifetime by each member of a known set of individuals, or "Lifetime Reproductive Success (LRS)" is an important measure indicating fitness differences between the sexes or among individuals that live under different social or ecological conditions. Studies of LRS are essential for a broad understanding of adaptation in a social context. Professors Smith and Dobson will measure LRS for a natural population of black.lipped pikas ( Ochotona curzoniae ), small mammals related to rabbits that inhabit alpine meadows on the Qinghai.Tibetan Plateau. Black.lipped pikas present a model system for such an investigati on because: 1) high mortality rates cause a nearly complete annual turnover in the population; 2) high population density ensures a large number of cohesive families (the primary social unit); 3) most environmental factors associated with LRS can be easily measured; 4) among families a variety of mating systems (monogamy, polygyny, polyandry) are simultaneously present; and 5) these mating systems are formed annually during a short episode of male dispersal, and once formed each family mating system remains stable throughout the year. These characteristics allow for contrast of LRS between males and females concurrently occupying different mating systems.