Population dynamics of Didelphis marsupialis in northern Colombia

A population of the common opossum, Didelphis marsupialis, inhabiting a highly degraded agricultural area in northern Colombia was studied by live-trapping for over two years. Three transects were established in strips of riparian vegetation within a matrix of agricultural crops. Sampling was performed once in October 1993 and then monthly from August 1994 through December 1995. Four population-level characteristics were estimated: abundance, sex ratio, age structure, and breeding activity. Abundance was very high at the beginning of the study but declined dramatically and then fluctuated at low numbers. The sex ratio did not vary among high-abundance, decline, and low-abundance population phases, but there was a deficiency of females with young at high abundance and of adults during the decline. The impact of these characteristics on the population dynamics of D. marsupialis is discussed with special emphasis on reproductive traits. These characteristics may also contribute to the potential of D. marsupialis as a reservoir for a wide variety of infectious agents.