A wide variety of plants, ranging in size from forest floor herbs to
giant canopy trees, rely on animals to disperse their seeds. Typical
values of the proportion of tropical vascular plants that produce fleshy
fruits and have animal-dispersed seeds range from 50-90%, depending on
habitat. In this section, the authors discuss this mutualism from the
plant's perspective. Herrera begins by challenging the notion that plant
traits traditionally interpreted as being the product of fruit-frugivore
coevolution really are the outcome of a response-counter-response kind
of evolutionary process. He uses examples of congeneric plants living in
very different biotic and abiotic environments and whose fossilizable
characteristics have not changed over long periods of time to argue that
there exists little or no basis for assuming that gradualistic change
and environmental tracking characterizes the interactions between plants
and their vertebrate seed dispersers. A common theme that runs through
the papers by Herrera, Denslow et at., and Stiles and White is the
importance of the 'fruiting environment' (i. e. the spatial
relationships of conspecific and non-conspecific fruiting plants) on
rates of fruit removal and patterns of seed rain. Herrera and Denslow et
at. point out that this environment is largely outside the control of
individual plant species and, as a result, closely coevolved
interactions between vertebrates and plants are unlikely to evolve.