Effects of Seed Shadows on Population and Community Patterns of Seedling RecruitmentEPA Grant Number: FP916433
Title: Effects of Seed Shadows on Population and Community Patterns of Seedling Recruitment
Investigators: Poulsen, John R.
Institution: University of Florida
EPA Project Officer: Michaud, Jayne
Project Period: January 1, 2004 through December 31, 2007
Project Amount: $104,762
RFA: STAR Graduate Fellowships (2004) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Fellowship - Terrestrial Ecology and Ecosystems , Ecological Indicators/Assessment/Restoration
Seed dispersal is the main process linking the spatial pattern of adult plants with that of their offspring. The spatial pattern of dispersed seeds frequently has been described as the template from which community patterns develop, implying a causal relationship in which adult spatial patterns reflect seed dispersal patterns; however, several ecological processes operate on the various life history stages between dispersal and recruitment of adults and have been shown to uncouple seed deposition patterns from the spatial patterns of adults. This project has two objectives. The first objective is to test how important the specific spatial distribution of seeds is for explaining the abundance and distributions of seedlings for a suite of species in a tropical forest community. The second objective is to examine how different patterns of seed dispersal for one species influence community abundance and composition within the local neighborhood of tropical trees.
This project has three complementary stages. First, I will quantify seed shadows of six animal-dispersed tree species. These data will serve as baseline data for subsequent manipulations of seed shadows. Second, I will compare seed and seedlings shadows across the six focal species to investigate potential spatial concordance between seed and seedling distributions. Finally, for three species, I will experimentally manipulate seed shadows around conspecifics to determine if the spatial distribution of seeds influences the seed-to-seedling-transition probabilities of the focal species. Three experimental distributions will be tested: (1) natural distribution mirroring real seed dispersal patterns; (2) uniform pattern representing a high rate of seed dispersal where seeds are dispersed at the same density throughout the local neighborhood of the tree; and (3) an aggregated pattern representing the absence of active dispersal. By monitoring seedling emergence and survival of heterospecifics in each of the experimental seed distributions, I also will determine whether the dispersal kernel influences the community abundance, diversity, and distribution of seedlings.
Tropical forests and their biodiversity are increasingly threatened by anthropogenic modification of habitats, as evidenced by the fact that the amount of forest remaining in central Africa is estimated at 55 percent of its original area. In particular, hunting has been suggested to significantly decrease abundances of tropical seed-dispersers and is unsustainable over the entire Congo Basin for 60 percent of African mammals. By experimentally comparing seedling recruitment when there is no dispersal (aggregated distribution) to natural and high levels (uniform distribution) of dispersal, I test whether the loss of seed dispersers should be expected to affect forest regeneration, altering seedling abundance and diversity.