Mutualistic interactions are characterized by weak species interactions (low rates of benefit acquisition) and are predicted to be extinction-prone, but data show long-term persistence. The challenge for theory is to identify mechanisms that promote the persistence of weak mutualistic interactions. Data suggests that competition for the benefits provided by mutualistic partners is common in nature. Yet, theory has not investigated whether competition for benefits alone can promote the persistence of weak mutualistic interactions.                                                                          Photo by Roy Johnson

I develop mathematical models to investigate whether competition for benefits alone is sufficient to allow the persistence of obligate pairwise interactions and the assembly of more complex communities. I find that competition for benefits alone is sufficient to promote the persistence of pairwise mutualistic interactions and the assembly of a three-species community from an initially pairwise interaction. The key finding is that competition for benefits allows the persistence of both weakly- and strongly-interacting mutualistic partners. Thus, competition for benefits provides a biologically-realistic mechanism for the persistence of natural mutualistic communities.

The next step is to investigate whether competition for benefits provides a mechanism for the assembly of complex mutualistic communities observed in nature. I investigate whether a community formed of interactions between specialist, generalist, or specialist and generalist species is more likely to assemble and persist. Theory predicts that interactions between specialists and generalists are the most stable configuration. I elucidate the conditions under which (i) the three-species community persists in the face of species invasion and (ii) species invasion leads to the assembly of more complex communities.