A preliminary field study was conducted on moustached tamarin monkeys (Saguinus mystax) inhabiting Padre Isla, a small island in the Amazon Basin of northeastern Peru. Data presented indicate that groups are generally composed of 3-8 individuals including a single breeding female, 1-3 reproductively active males, nonreproductive adult females, and offspring. Migration of adults and subadults into and out of established groups is common, and it is unlikely that S. mystax social units represent nuclear or extended families. It is argued that rather than tending towards monogamy, the reproductive biology and mating activities of moustached tamarins are better understood in terms of a communal breeding system. In the case of this and perhaps other callitrichid species, such a system appears to involve female promiscuity and the participation of reproductively active adult male group members in caring for the young. The hypothesis that there is an important relationship between the number of adult male ‘helpers’ and infant survival is discussed.

In this paper we address a series of questions concerning reproductive opportunities, kinship, dispersal, and mating patterns in free‐ranging moustached tamarin monkeys (Saguinus mystax). Between 1980 and 1990 information on group size, composition, and migration patterns was collected on marked groups of moustached tamarins inhabiting Padre Isla, an island in the Amazon Basin of northeastern Peru. In 1990, 86% of 114 animals residing in 16 social groups were trapped, examined, and released. Mean group size was 7.0, including 2.2 adult males and 2.0 adult females. None of these groups was characterized by a single adult male‐female pair. In groups with more than one adult female, only the oldest female produced offspring. An examination of dispersal patterns indicates that transfers between groups were common and fell into several categories, including immigration of individual males and females, simultaneous transfer of pairs of subadult and/or adult males (sometimes relatives) into the same social groups, and group fissioning in which males and females of the splinter group join another small social group. We have no unambiguous cases of 2 adult/subadult females migrating together into the same social group. All 6 groups for which reproductive data were available were characterized by either a polyandrous or polygynous (polygyandrous) mating pattern. The results of this study indicate that moustached tamarins reside in small multimale multifemale groups that are likely to contain both related and unrelated adult group members. Kinship and social ties among males appear to be stronger and more longlasting than kinship and social ties among females. We contend that the modal mating system of moustached and many other tamarins is not monogamous, and offer the possibility that cooperative infant care and mating system flexibility in callitrichines evolved from a polygynous mating pattern. © 1993 Wiley‐Liss, Inc.

QuestionsSpatial pattern analysis may be used to derive hypotheses on the processes that shape plant communities. Do different mature semidesert communities exhibit the same major spatial patterns, suggesting that similar processes shape them?LocationNine localities in the Bolivian Andes.MethodsWe mapped all woody individuals at each locality. We performed uni‐, bi‐, and multivariate spatial analyses of nine Andean, mature semiarid plant communities to test for similarity in spatial patterns.ResultsWe found that the nine communities exhibited, in most of the main spatial pattern attributes, close similarities (community aggregation, importance of plant interactions, life form differences, etc.). Some peculiarities were likely due to differences in life form or site history.ConclusionsAt least for Andean semiarid communities, the complete analysis of a representative plot conveys reliable information on spatial relationships and, hence, on potential underlying mechanisms. This shows that the use of 1–2 representative plots can be used to extrapolate to similar communities within a given region. Our results can be used as a plausible hypothesis to be tested in other zones of the planet.

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