Colors of Fruit Displays of Bird-Dispersed Plants in Two Tropical Forests

Abstract

Color is a key characteristic of fruits because it affects the probability that they will be noticed or selected and, consequently, that their seeds will be dispersed. This paper examines the colors of fruit displays of 383 bird-dispersed plant species in two diverse tropical forests in Costa Rica and Peru. We detail the frequency of ripe-fruit color displays and try to explain these patterns by considering a general model of selection on fruit colors. The generalization that "bird fruits tend to be red" is shown not to apply to the Neotropics-most ripe bird fruits in our sample are black, with red being the second most common color. The proportion of plant species bearing either black or red fruits is remarkably similar in Costa Rica, Peru, Europe, and Florida (62%-66%). Certain color combinations in fruit displays, formed by ripe fruits plus contrasting unripe fruits or accessory structures (bracts, peduncles, persistent calyces), are especially common. The colors black and red, for example, co-occur in about 18% of all fruit displays in both Peru and Costa Rica, including species from 26 plant families. Some ripe-fruit colors (black, brown, blue, green) tend to be associated with unripe fruits or accessory structures of contrasting color; other colors (red, orange, white, yellow) tend to occur alone. We propose a model of fruit color suggesting that there is a cost of bearing conspicuous color patterns, either in attracting inappropriate consumers to the fruit or in manufacturing pigments or associated structures. Plants should be selected for increased conspicuousness of fruit display if the benefits of attracting more dispersers outweigh the costs of incidentally attracting lower-quality dispersers or of being limited in the number of fruits that can be produced. Plant species especially likely to benefit by attracting many dispersers include colonists of patchy habitats, plants with generalized seed and seedling requirements, and plants whose fruits are unlikely to be discovered or eaten because they are nutritionally poor, they occur in small crop sizes, or they grow under poor visibility conditions or at times when dispersers are scarce.