Colonization-extinction dynamics of opossums on small islands in Panama

We studied the distributions and colonization-extinction dynamics of five species of opossums (Didelphis marsupialis, Marmosa robinsoni, Philander opossum, Caluromys derbianus, and Metachirus nudicaudatus) on 12 small islands in Gatun Lake in central Panama. Opossums were censused by monthly livetrapping from 1991 (eight islands) or 1993 (four islands) through 1995. We recorded 75 colonizations over the course of the study. Didelphis marsupialis was the most frequent colonizer and accounted for 56% of all colonizations recorded. However, only four D. marsupialis populations that reproduced successfully resulted from these colonizations, and most populations went extinct. Marmosa robinsoni and P. opossum also frequently colonized these islands but rarely established successful populations. Multiple linear regression was used to relate the mean numbers of colonizations and population establishments per year and mean and standardized persistence times of all five species of opossums to island size and isolation. These four dependent variables were not related to island area or isolation distance. This system, characterized by frequent colonizations and extinctions, fit the mainland-island metapopulation model, and nearby mainland areas that maintained persistent populations of all five species provided colonists to the small islands.