A study on neotropical Didelphis (Mammalia, Polyprotodontia, Didelphidae)
The Haffer-Vanzolini model proposes that geographical variation and speciation of terrestrial organisms in South America can be explained in terms of the influence of pleistocenic climatic changes on vegetational distribution. During dry periods forests were restricted to small areas, which acted as "refuges" for sylvatic organisms. Geographical differentiation and sometimes speciation were a consequence of this isolation. In a preliminary survey of numerous mammalian taxa, it was found that distribution patterns concorded well with, the model, which also suggested explanations for the origin and extinction of species and higher taxa. The ecology of any taxon must however be taken into account when considering how paleolandscapes might have influenced its present distribution. The genus Didelphis was studied in detail. The major climatic, orographic and vegetational factors relating to 289 locality records, were analysed. It is shown that one ensemble of the D. albiventris group inhabits dry deciduous forests, meadows, Thornbush (Caatinga and Chaco), the Monte and the Cerrados. Another ensemble is associated with the Oreal domains of the Andes, but avoids higher altitudes with extremes of dry and cold. These two ensembles appear to be linked through the Monte domain. The D. marsupialis group is restricted to rainforests and cloud forests. Those inhabiting northern South America are separated by at least 800 kilometers from an ensemble of populations living in the Atlantic and Araucaria forests. Geographical variation of the D. marsupialis group along transects linking sampling localities was assessed statistically and it is shown that the patterns of variation are well in agreement with the Haffer-Vanzolini model. Correlation pleiades show differences between the ensemble of populations in northern South America and those in eastern Brazil, and it is suggested that these two ensembles are distinct at the species level. The observed differences in correlation pleiades between females and males is discussed. Some data on reproduction of D. Albiventris is presented.