Seed Dispersal by Animals: Contrasts with Pollen Dispersal, Problems of Terminology, and Constraints on Coevolution

Abstract

Theoretical and empirical research on frugivory and seed dispersal has been influenced by concepts derived from the study of pollination. In particular, explicit and implicit analogies between seed dispersal and pollen dispersal have led to the expectation, under certain conditions, of the evolution of obligate, species-specific relationships between fruiting plants and the animals that disperse their seeds. The two systems differ in important respects, however. Plants benefit by directing pollen dispersers to a definite, recognizable "target," a conspecific flower, and they can provide incentives at flowers which serve to attract potential pollinators. In effect, there is "payment upon delivery" of the pollen. In contrast, for seeds the target (an appropriate site for germination and establishment) is seldom readily discernible, and dispersal beneath a conspecific plant may actually be undesirable. Another important difference is that frugivores are "paid in advance." Because of these differences and others, the outcomes of coevolution of fruiting plants and frugivores are expected to be different than those of flowering plants and flower visitors. There are therefore problems with drawing analogies between the two systems and using terminology derived from studies of pollination to design and interpret studies of seed dispersal