PARENT SESSION
Oral Session #3: Plant Population Ecology. Presiding: N. Fetcher.
Monday, August 6, 2001. 8:00 AM to 11:30 AM. Hall of Ideas L&M.
Contributions of seed dispersal and demography to recruitment limitation in a Costa Rican cloud forest.
Murray, Greg1, Garcia, Mauricio1, 1
ABSTRACT- We propose that recruitment limitation is especially important in facilitating the coexistence of 30-40 species of pioneer plants in a Costa Rican cloud forest where windthrow and landslide are the predominant disturbances. We monitored seed rain and survivorship, and assessed standing crops of dormant seeds in the soil, along 2.5 km of transects for three years. Despite high overall density (ca. 3000-6500 seeds m-2), the seed bank was exceedingly patchy: most pioneer species occurred in < 25% of the soil samples, and only two were predictably present in all samples. Much of this spatial heterogeneity was present at the time of seed deposition, but spatial patterns were modified by the activities of seed predators and pathogens. Species that accumulate in the soil over long periods (some to more than 100x the density of annual seed rain) tended to become more patchily distributed over time, while those with rapid turnover became more uniform. Post-dispersal mortality thus increases spatial heterogeneity of some species and decreases it in others. Predator and pathogen exclusion experiments demonstrated complex patterns of mortality among Monteverde pioneers that were generally consistent with independent measurements of accumulation in the soil. Recruitment limitation may play an important role in preventing competitive exclusion among pioneers, with the causative spatial heterogeneity being produced at both the seed dispersal and seed survival stages of recruitment.
KEY WORDS: dispersal limitation, seed bank, seed demography, pioneer plants