SEED DISPERSAL OF BURSERA FAGAROIDES (BURSERACEAE): THE EFFECT OF LINKING ENVIRONMENTAL FACTORS

We studied the seed dispersal process of a population of Bursera fagaroides (Burseraceae) on the coast of the Gulf of Mexico by considering 1) all phases of the dispersal process (i.e., fruit removal, effect of seed passage through digestive tract, seed deposition, removal of seeds from the ground, germination, growth and survival of seedlings and adults, and seed set); 2) plant and animal components and their interaction; and 3) spatial variation in these components using different subpopulations. Hill aspect and surrounding microenvironment or habitat affected individuals of B. fagaroides, and this effect depended on life stage (seed, seedling, or adult). Seed germination was greater in moderately-shaded areas (below the perennial plant species Coccoloba barbadensis) than in relatively open sites (below B. fagaroides or on bare sand); seedlings grew less on sites in bright sunlight; adult individuals were not detected in highly-shaded places; and females inhabiting open sites (grassland) had more removed seeds than those of shaded areas (shrubland and dry forest). Vireo griseus and Dumetella carolinensis, the only species consuming fruits of B. fagaroides during our study, differed in their effect on seeds: seeds ingested by V. griseus did not germinate, whereas 17% of seeds ingested by D. carolinensis germinated. Additionally, even though both bird species preferred the tropical dry forest, their foraging behavior differed. Vireo griseus was mostly found at mid-canopy height in tree-dominated sites, and D. carolinensis used the understory of shrubby areas; B. fagaroides does not inhabit tree-dominated sites. Our results indicated that there was no best place for a seed to land. What is suitable for a seed might not be optimal for a fruiting plant. Thus, patterns of seed dispersal are almost certainly altered by processes that happen long after seed deposition.