Populations of feral pigs (Sus scrofa) and Philippine deer (Cervus mariannus) have sustained populations in the Micronesian island of Guam for centuries and are believed to have severe impacts on native forests. Grazing and uprooting damage have been observed from both animals, but other impacts such as seed dispersal have not been investigated. Pigs and deer may act as dispersers of invasive species, as is suspected for feral pigs in Hawaii. To test whether deer or pigs could potentially act as dispersers, deer and pig scats were collected from forest areas in Guam. They were then planted and monitored in a nursery. Fifteen deer pellet groups and twelve pig scats were mixed with soil and watered daily. Any new sprouts were counted and identified.
Results/Conclusions
A high number of seedlings germinated from all of the pig scats collected, almost 100% of which belonged to two species of abundant, fast-growing fruit trees (Carica papaya, an invasive, and Morinda citrifolia, a pan-tropical but likely native tree). Several pig scats had over 100 individual sprouts of C. papaya and over 30 individuals of M. citrifolia. Deer pellets were less productive, but several species did emerge in low numbers including Leucaena leucocephala, Pilea microphylla, and Triphasia trifolia, all invasive species. These results indicate that endozoochory in both species may be playing a role in the species composition and abundance of plants in Guam's forests, habitats that have lost most of their primary seed dispersers (extirpation of forest birds by invasive brown treesnake). However, the abundance of common invasive species in scats indicated endozoochorous dispersal by deer and pigs could be detrimental to Guam’s forests.
