DISSERTATION RESEARCH: An Experimental Test of the Relationship Between Seed Predator Density and Recruitment Limitation in Tropical Trees

University Of California-Davis, Davis CA

Investigators

Abstract

Abstract- Rejmanek, Marcel (0309408) The processes that are responsible for maintaining the high levels of diversity of trees in tropical forests are not well understood. There is increasing evidence that a particularly important process is recruitment limitation, where the seeds of many species do not reach sites favorable for germination and growth before the seeds of another species do. As a result, less competitive species are able to persist simply by virtue of getting a head start in growth over more competitive species. However, recruitment limitation may not be due entirely to chance. Instead, it more often may be an outcome of the "opportunity" seeds have to be dispersed. Many animals are important consumers and dispersers of seeds, and it can be expected that whether a seed gets eaten or dispersed and cached depends on the type of animal handling the seed, how many animals there are in an area to handle the seed, the relative preference animals have for any particular type of seed, and where the animal caches the seed. It has been hypothesized that more seeds will be dispersed and cached when seed-eating animals have more food, but this has not been experimentally tested. This research would test this hypothesis with an experiment focused on three species of palm with different sized seeds, and the spiny pocket mouse (Heteromys desmarestianus), the dominant mammal seed predator/disperser in the lowland rainforests of Belize. The abundance of H. desmarestianu would be experimentally reduced, and then seed removal and dispersal rates, and where seeds are cached between plots with and without reduced abundance of H. desmarestianus would be compared. This is the first study to experimentally test the relationship between seed predator density and recruitment limitation in tropical forests, and is a collaboration between scientists from UC Davis, the Belize Foundation for Research & Environmental Education, and the University of Belize. Funding has been provided through a Dissertation Improvement Grant from the Directorate of Biological Science, with additional funds from the International Science and Engineering Program.