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
southeastern Brazil, from 1995 to 1998. Males, but not females, were observed to move between populations. Estimated
sizes of the populations 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 term
only. Small population sizes, synchrony and presumable male-biased migration are all likely to make the set of
populations more vulnerable to extinction than expected for a metapopulation.