Opossums are effective seed dispersers of fruits not consumed by birds and bats.

Juvenile of white-eared opossum - Photo Omar Saguir
In his bachelor's thesis, Nicolás Duprez studies the effectiveness of opossums as seed dispersers
The tamarillo is not only consumed by humans, it is also one of the fruits preferred by opossums in the Andean forests.

Seed dispersal by frugivorous animals is an ecological process that influences the dynamics of plant species, the functioning of ecosystems and the restoration of degraded landscapes. The main animals involved in this interaction are species of birds, bats and various groups of non-flying mammals. In the mountain forests of northwest Argentina (known as "southern Yungas"), we know a lot about seed dispersal by birds and bats, but there is a large knowledge gap about the role of non-flying mammals (terrestrial and arboreal species).

To strengthen our knowledge about the role of these mammals in plant-animal interaction networks of the southern Yungas, we began to study an abundant and widely distributed species in these forests: the white-eared opossum (Didelphis albiventris). In his bachelor's thesis project, Nicolás Duprez is using cafeteria trials to determine the preferences of opossums for different species of fruits, and controlled germination trials to determine the effectiveness of opossums as seed dispersers. To achieve his objectives, he works with three juvenile individuals of the white-eared opossum. All three animals suffered events that separated them from their mother, and were brought to the Horco Molle Experimental Reserve (belonging to the National University of Tucumán) for recovery and their eventual reintegration into nature.

The preliminary results are very interesting. As expected, based on what we know of the species' diet in other areas of South America, the opossums consumed most of the fruits that were offered to them. What is novel is that the three individuals showed similar patterns of preferences for the various fruit species offered. Furthermore, the two most preferred species (wild papaya, Vasconcellea quercifolia, and tamarillo, Solanum betaceum) are not consumed by birds or bats, illustrating the complementary role of opossums as seed dispersers in the complex network of plant-frugivore interactions of the southern Yungas.

In addition, the germination experiments indicated that, for most of the fruit species evaluated, seeds recovered from faeces have high germination rates similar to control seeds. This shows that the consumption of fruits by the white-eared opossum results in the dispersal of viable seeds, indicating that they are able to act as effective seed dispersers in the region. Overall, this is an important step to understanding how non-flying mammals are integrated, and what role they play, in the seed dispersal networks of subtropical Andean forests of northwest Argentina.