Population dynamics of four marsupials and its relation to resource production in the Atlantic forest in southeastern Brazil

Variations in mammal population sizes can be related to the availability and abundance of their resources. This study reports the population dynamics of four didelphid marsupials (Didelphis aurita, Philander frenatus, Marmosops incanus and Metachirus nudicaudatus) and its relation to litter fall, used as a measure of resource production. A capture-mark-recapture study (CMR) was carried out in a disturbed area of the Atlantic forest in Rio de Janeiro State, Brazil, in three grids in the locality of Garrafao from April 1997 to February 1999, every other month. Litter was collected every month using 15 squared litter traps of 0.25 m(2) in the grids (5 in each grid). Leaves, twigs, reproductive structures and total litter fall rates were calculated as tons ha(-1) month(-1). Population densities, survivorship and recruitment rates were estimated. For D. aurita and P. frenata, population densities were correlated positively only with litter production. For M. incanus, population density was correlated positively with survivorship, litter production and negatively with rainfall. M. nudicaudatus population density was correlated only with recruitment and twigs abundance. The availability of fruits and arthropods had a large influence in the proximal causes on the variation of small mammal populations. In forests where there is an adequate rate of decomposition of the litter, we may understand how resources influence population variation, and litter becomes the base of resources for such marsupials in the Atlantic forest.