Distribution of four-eyed opossum, Philander opossum (Marsupialia, Didelphidae) on small islands in Panama

The distribution of Philander opossum (gray four-eyed opossum) on islands in Gatun Lake (central Panama) was determined by conducting a live-trapping census of 50 small islands. Presence-absence in relation to island size and isolation was modeled using multiple logistic regression analysis. Probability of occurrence of P. opossum was positively related to both island size and isolation. Thus, larger isolated islands had higher probabilities of occurrence of this opossum. This result is surprising since proximity to mainland sources generally promotes occurrences of mammals on islands. Most of the occupied islands were located within a small isolated cluster of islands. We suggest that 1) P. opossum on the larger islands within this cluster have flourished in the absence of major predators and that they maintain persistent populations, 2) these larger islands serve as sources of immigrants for neighboring islands that are too small to support persistent populations, and 3) populations on the smaller islands are prone to extinction but are subsequently recolonized. This apparently dynamic system of P. opossum populations on islands, particularly within the ''hot-spot'' cluster of isolated islands, fits the Boorman-Levitt metapopulation model.