Consumption of fruits of the Melastomataceae by birds: how diffuse is coevolution?

Abstract

The family Melastomataceae shows two major modes of dispersal for its small seeds: wind for capsular fruits, and birds for berry-type fruits. Distribution patterns of these two dispersal types differ. We focus on evolutionary diversification of bird-dispersed melastomes in the New World, in relation to that of their avian dispersers. We first examine in detail patterns of melastome fruit availability and consumption by understory birds in a Costa Rican rain forest. Although a relatively small portion of total fruit available in most months, melastomes comprised a major component of the diet of all bird groups studied, most notably manakins and most tanagers, which in turn were the major consumers of melastome fruits. Examination of data from several other neotropical areas confirms the importance of the manakins and tanagers as the avian frugivores most closely associated with the melastomes. These two groups differ in their manner of fruit consumption, being ‘gulpers’ and ‘mashers’, respectively. The patterns of species richness of small mashers in several Neotropical areas conform very closely to the distribution patterns of bird-dispersed melastomes; both are most speciose in wet forests of middle elevations. Gulpers, especially manakins, are most diverse at low elevations. Thus, the small-seeded melastome berry appears to have evolved primarily in association with masher-type frugivores such as tanagers; with the later addition of manakins to their disperser spectrum, the melastomes may have increased greatly in local abundance, but not (yet?) in diversity, in the wet lowland neotropics.