Seed Prcdaíion by Mammals and Forest Dominance by Quercus olcoides, a Tropical Lowland Oak

Abstract

Quercus olcoides Cham. and Schlccht is an unusual íree in several respects: ¡t is an oak found in neotropical lowland forests. its distribution is not continuous but rather dividcd into many patches of various sizes, and it is a dominant in all the forests in which it occurs, attaining densities far higher than most species of tropical trees. This dcnsity pattern is related to the vulnerability of Q. olcoides acorns to predatiort by mammals. Observations of agoutis, deer, peccarics, squirrels, pocket mice and otber seed consumers in Santa Rosa National Park, Costa Rica, showed that thcse mammals act only as predators, not dispersers, of Q. olcoides acorns. Experiments which involved placing acorns in deciduous forest where Q. olcoides does not occur. demonstrated that, due to high predation rates, the rvurr^M^ of acorns produced by an isolated tree is far too low for adiílfs to replace themselves. Ip'óak forest, on the other hand, where the combined acom • crops of many oaks satiate the seed predators, acorn survivorship • until g^rmination is high enough to maintain the population. Furtliermore. acom survivorship in oak forest areas is inversely profjortional to the apparent mammal dcnsity in those areas. Thu| tÁe pattern of forest dominance and patchy distribution is related to positively density-dependent acorn survivorship: w heife Q. olcoides is the forest dominant. it will survive, but if its- dcnsity falls to the level typical of tropical trees, it will eo ldcallv extinct.