ON THE BIOLOGY OF MOUSE OPOSSUM THYLAMYS ELEGANS (DIDELPHIDAE, MARSUPIALIA) IN THE PROVINCE OF TARIJA (BOLIVIA)

The karyotype of Th. elegans was studied. The animals are insectivorou s. Tile opossums consume different invertebrates (in al eas with reduc ed species diversity they can feed mainly on ants). The peculiarities of the species are fat deposits in the tail and the ability to fall in to tol por under food deficiency or low temperatures. Female does not rear off spring in its pouch. After the pelage in youngs, when their e yes are still closed, a female carries offspring on its back, the youn gs are clinging to its fur. Three age groups of animals (adults, subad ults and youngs) were distinguished during the breeding season. At the end of the breeding season, only subadults and youngs were observed. The animals occured in different habitats. They had wide dispersion an d low total number. The social interactions are characterized by low d iversity and mainly agonistic type of interactions. Th. elegans is con sidered to be a species, that uses its area always moving into the hab itats, where food is seasonally abundant. The negative reaction to con specific animals prevents high local abundances. The fat storage in th e tail enables the animals to move into tile territories without suffi cient food resources and exploit extensively the dispel sed temporaril y favorable habitats. The wide range of local migrations of animals en ables them to reoccupy the habitats periodically destroyed by human ac tivity and favours tile survival of their populations in localities ch anged by human activity. The low numbers are the natural characteristi c of populations, not the result of anthropogenic influence.