Does the disruption of the keystone interaction by non-native ungulates produce cascading effects on the community?
Non-native ungulates produce cascading effects on pollination networks by disrupting the keystone interaction but produce only marginal impacts on seed dispersal networks. Non-native ungulates caused the ecological extinction of the marsupial and reduced the ecological importance of the mistletoe, preventing its recruitment and leading currently its population to extinction. Pollination networks are much simpler and less stable in invaded sites than in intact forest sites with the keystone interaction, presumably because these sites support fewer direct and indirect interactions and fewer generalist plants and pollinators. The low interaction diversity in invaded sites concentrates the energy flow in few pathways, reducing the persistence and stability of pollination networks (Mougi & Kondoh 2012). Similarly, the simplification of ecological networks has been demonstrated for others human disturbances (Albrecht et al. 2007; Tylianakis et al. 2007; Galianaet al. 2014). Moreover, the low number of plants and pollinators that occupied positions with high number of direct interactions makes the network susceptible to generalist species extinction when non-native ungulates are present.
On the other hand, we found no cascading effects on seed dispersal network despite the high vulnerability of this forest to the loss of mutualistic interactions. The impact of non-native ungulates on seed dispersal networks may be attenuated by the strong presence of the most generalist bird seed disperser of this forest, Elaenia albiceps(Amico & Aizen 2005). This migratory bird is abundant in summer, overlapping with fruit ripening and playing a critical role forest regeneration (Bravo et al. 2015).