Evolution and history of tropical forests in relation to food availability - Background

Because plant-frugivore interactions are not species-specific, there is potential competition, not only among frugivores, but also among plant species for the services shared by dispersal agents. This competition has driven evolutionary increase in the reward offered to seed dispersers, up to limits presumably set by a balance between cost and benefits of dispersal. How concentrated the nutritional reward for frugivores is, may depend on the intensity of competition for the services of frugivores. Competition may select for increased reward; alternatively, it may select for an altered phenology that minimizes competition. Variation in concentration of the reward may also reflect the "packaging" problem inherent in fleshy fruits. Larger seeds have more reserves and a better chance of survival; but larger seeds mean larger diaspores. The larger the diaspore, the smaller the number of animals large enough to exploit the fruit: Thus when seed size is near the upper limit. This may explain why many species evolved a fruit with a thin - but very fatty- aril surrounding a large seed, and why the fruit of several Palmae also have this "optimum packaging system" with a pulp relati vely thin but rich in fat and/or starch