Does the role that frugivorous bird species play in seed dispersal networks influence the speed of evolutionary divergence?

Extensive work on plant-animal mutualistic networks has shown that species in such networks vary in their number of connections with other species, from highly connected species ('super-generalists') to those connected only to a few other species ('specialists'). How these species with different degrees of network specialization differ in their speciation rate remains largely unexplored. Here we hypothesize that having many interaction partners lowers the amount of leverage of any one partner, and slows coevolution. We then explored the speciation rate in frugivorous birds in a dataset of published seed dispersal networks, using a recent phylogeny that has a date for the divergence time of all bird species from their most closely related sister taxa. We found that generalist species' divergence time was longer than specialist species'. While there may be other correlated traits to specialization that could contribute to this result, specialists and generalists did not vary in the size of their global distributions, and thus specialists are not simply rarer, if the size of the distribution reflects the species' abundance. We discuss whether similar tests can be applied to other kinds of plant-animal interactions, and what level of taxonomy is appropriate to investigate to answer these sorts of questions.