Understanding the impacts of global change on mutualistic networks is a
major challenge in modern ecology. The gain or loss of particular
species and the disruption of key interactions are both consequences and
drivers of global change that can lead to the disassembly of complete
mutualistic webs. We explored whether the disruption of a
hummingbird-mistletoe-marsupial keystone interaction by the invasion of
non-native species can have cascading effects on both pollination and
seed dispersal networks in the temperate forest of Patagonia. We found
that the disruption of the keystone interaction resulted in diverse
indirect effects that led to less complex pollination and seed dispersal
networks. Similarly, the disruption of the keystone interaction
decreased the functional redundancy among generalist plants and
pollinators. Our results demonstrate how the disruption of a keystone
interaction can have cascading effects through the community, reducing
the complexity and stability of ecological networks.