Competition for Dispersers, and the Timing of Flowering and Fruiting in a Guild of Tropical Trees

Abstract

One conceivable outcome of competition for a limited number of pollinators or seed dispersers is the evolution of minimally overlapping flowering or fruiting seasons. In the lower montane forests of Monteverde, Costa Rica, a study of 23 tree species (Lauraceae) that share avian seed dispersers and insect pollinators found little evidence for such phenological character displacement. The distribution of flowering phenologies appeared random but were indistinguishable from a uniform sequence; fruiting seasons were more aggregated and were significantly non-uniform. Nonetheless, ecological competition for seed dispersers apparently does occur because fruit removal rates decline when many species fruit concurrently. Neither intraspecific variance in phenologies nor duration of flowering or fruiting within species was correlated with interspecific competition for dispersers. Final fruit weight at maturity explained only about a quarter of the variance in developmental times between species. The absence of overdispersed phenologies cannot exclude the possibility that competition exists or that phenological character displacement has occurred. Uniformly distributed phenologies have been reported more frequently for flowering than for fruiting. Because flowering plants face reproductive as well as ecological competition, I hypothesize that selection may be stronger for the divergence of flowering times than for fruiting times, especially within guilds of related species.