Patterns of population fluctuation, reproductive activity and age structure were studied in populations of the marsupial, Micoureus demerarae occupying two small (7.0 and 8.8 ha) fragments of Atlantic Coastal Forest in southteastern Brazil, from 1995 to 1998. Males, but not females, were observed to move between populations. Estimated sizes of the populatious in each fragment were very small, usually below 20 individuals. Breeding usually occurred from September to April. Population peaks came mostly by the end of this season, the delay reflecting the time required for the young to become trappable. In August 1997, the area was hit by a fire severely affecting the smaller fragment. Populations were synchronous before the fire, although they became asynchronous after it, possibly in the short tcr m only. Small population sizes, synchrony and presumable male-biased mig ration are all likely to make the set of populations more vulnerable to extinction than expected for a metapopulation.o TEXTO COMPLETO DESTE ARTIGO, ESTARÁ DISPONÍVEL À PARTIR DE AGOSTO DE 2015.173339352