Testing the dispersal syndrome hypothesis on Ficus (Moraceae): The effect of color, odor, and size on fig preference by birds and mammals

Studies of fruit evolution try to explain the tendency of brightly colored fruits to be odorless and small based on the Dispersal Syndrome hypothesis (DSH). This hypothesis predicts that, because birds have acute color vision, a poor sense of smell, and commonly swallow fruits whole, they should select for brightly colored, odorless, small fruits. Because mammals rely more heavily on odor than on visual cues for finding fruits, and often eat fruits piecemeal, they should select for dull-colored, odorous, large fruits. But, do mammals and birds really prefer fruits with the combination of fruit traits predicted by the DSH? I explore this question on fig trees (Ficus, Moraceae) of a lowland forest in Papua New Guinea by videotaping fruiting trees during the day and night (using an infrared light source) to record tree visits by frugivores. This non-intrusive method permits unbiased, uninterrupted observations under natural conditions unlike previous studies, which have used captive animals in non-natural situations, or have largely ignored nocturnal mammals due to the difficulty of their observation. Results indicate that frugivores prefer fruits with the combination predicted by the DSH, and they emphasize the importance of odor for mammals. Mammals most commonly feed on large, dull-colored, odorous figs, but they may also feed on small, red fruits if they have a strong odor. Birds consume only small, red figs, whether they are odorous or not. Understanding frugivore choice is essential to elucidate the importance of seed dispersers in the evolution of fruit traits.