The Influence of Fruit Size and Structure on Composition of Frugivore Assemblages in New Guinea

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Abstract
In a mid-elevational rainforest in New Guinea, size and structure of fruits influenced feeding visits by various species of frugivorous birds: large (diam. > 12 mm) structurally unprotected fruits were taken mostly by fruit-pigeons and bowerbirds, structurally-protected fruits were taken mostly by birds of paradise, and small, structurally-unprotected fruits were taken by nearly all species. Fruit-pigeons as compared with birds of paradise have short, thin bills; small feet; and fewer behaviors for reaching and handling fruits. Birds of paradise use complex food-handling techniques for removing fruits in capsules and other protective structures that are similar to techniques used to capture insects hidden in bark and dried foliage. Absence of large structurally-unprotected fruits in the diets of birds of paradise is not explained entirely as an effect of fruit size. Specialization for frugivory in the entirely frugivorous fruit-pigeons has resulted in exploitation of specific fruit types (large and small structurally-unprotected fruits) rather than all fruit types. Most fruiting plants were visited by a subset of frugivores, as influenced by fruit size and structure. Attracting specific feeding assemblages might be regarded as an adaptation of the plant for enhancing particular patterns of seed dispersal. However, other selective pressures also operate on the evolution of fruit size and structure.