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).