On the Evolution of Masting Behavior in Trees: Predation or Weather?

We address the problem of parasite-mediated selection for the evolution of masting (episodic, synchronized seed production) in trees. As a strategy, masting works very well in swamping seed predators when it is common in the population. It is not clear, however, how such a behavior can invade a nonmasting ancestral population when parasites and predators are kept at high densities by an annual abundance of fruits. We demonstrate that rare masting behavior enjoys higher fitness than nonmasting, as long as seed parasites are aggregated and all masters are perfectly synchronized. We develop a dynamic optimization model that demonstrates that synchronized fluctuations in seed production can develop as long as there is some year-to-year variation in weather-mediated resource availability. We suggest that synchronized fluctuations in seed production must exist before any predator or parasite can select for masting.