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.