Conclusion
One or a few species and their direct and indirect interactions can be
critical to maintain the structure of communities and ecosystem
processes. Thus, identifying which species or interaction to conserve is
critical to prevent cascading effects in the community. Here, we have
demonstrated the role of a hummingbird-mistletoe-marsupial mutualism as
a keystone interaction in Patagonian temperate forest and the cascading
impacts of the disruption of this interaction by non-native ungulates.
We analyzed interaction motifs as the building blocks of pollination and
seed dispersal networks, and found that the
hummingbird-mistletoe-marsupial mutualism increases complexity on
pollination and seed dispersal networks, supporting a high diversity and
frequency of complex motifs and improving the persistence of the
community. In addition, the keystone interaction can increase the
robustness of pollination networks to generalist species extinction due
the high number of plant and pollinator species at generalist motif
positions. Moreover, we found that non-native ungulates disrupt this
keystone interaction, affecting the ecological importance of the
mistletoe and marsupial and reducing the complexity and stability of
pollination networks and, marginally, of seed dispersal networks.
Recognizing the keystone interactions is essential to achieve the
conservation of communities due its role to maintain the structure and
functionality of them, especially in the current scenario of global
biodiversity loss and spread of invasive species. Moreover, incorporate
indirect effects in ecological studies is necessary to increase the
realism of global changes impacts on communities, widely underestimated
when direct effects are only considered.