Is the hummingbird-mistletoe-marsupial mutualism a
keystone interaction?
Network complexity - We found different complexity for both
pollination (F 1,7 = 7.021, P = 0.031) and
seed dispersal (F 1,6 = 4.794, P = 0.028)
networks between intact forest sites with and without the keystone
interaction. We found that in sites with the keystone interaction both
pollination and seed dispersal networks were supported by 35% and 47%
more different motifs respectively, and hence by greater direct and
indirect ecological interactions, than networks in sites without this
interaction (Fig. 2a and 2c). In addition, both pollination and seed
dispersal networks had 29% and 12% greater frequency of largest motifs
integrated by six species in sites with the keystone interaction than in
sites without it (Fig. 2b and 2d), which suggests a greater proportion
of complex interactions supporting these networks.
Functional redundancy among generalist species - The number of
pollinator and plant species that occupied generalist positions was over
three times higher in intact forest sites with the keystone interaction
than in forests without it (Fig. 3a; Table S3). Moreover, in sites
without the keystone interaction no pollinator species occupied the most
generalist position and they barely occupied the second one. This
analysis was not possible in seed dispersal networks because of the
reduced number of frugivorous species.
Ecological importance of the keystone interaction members - We
found differences in the ecological importance of the mistletoe
(Z 1,7 = 3.452, P < 0.001) and
the hummingbird (Z 1,7 = 2.579, P =
< 0.001) but not on the ecological importance of the marsupial
(Z 1,7 = 0.941, P = 0.146) between intact
forest sites with and without the keystone interaction (Fig. 3b). In
sites with the keystone interaction, the mistletoe and the hummingbird
occupied 10x and 29x more positions than in sites without this
interaction. These results suggest a greater ecological importance of
these species in pollination network because they exert more direct and
indirect ecological interactions.