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Seedling Recruitment and Diversity in a Tropical Rainforest

Principal Investigator: C. E. Timothy Paine, PhD candidate, Lousiana State University

I am most interested in the maintenance of biodiversity. I take an experimental approach to understand the relative importance of the ecological forces acting to maintain the diversity of a tropical rainforest. I primarily work with seeds and seedlings, as they are more amenable to manipulation than are canopy trees. I have three projects underway at Cocha Cashu which will form the core of my dissertation.

Do Seedlings Compete?
In most habitats, it is believed that competition is a dominant force structuring plant populations and communities. In the heavily shaded understory of tropical rainforests, this may not be the case. If seedlings do not compete among themselves, their trajectories of growth and survival may be substantially independent of density. Three coupled experiments on the seedlings of Matisia cordata (Bombacaceae) investigate this possibility. Excavations directly illustrate the
overlap of seedling root systems. The uptake of a nutrient tracer indirectly indicates the extent of root systems. And a clipping experiment illustrates the impact of density on growth and survival.

Dispersal vs. Establishment
Both processes of seed dispersal and seedling establishment have been elegantly shown to contribute to the maintenance of diversity. In these seed-addition experiments, I investigate their relative importance, and how their effects vary over time. If interactions among seedlings are
weak, or if seedlings are insensitive to environmental conditions, then seedling recruitment wil be governed primarily by dispersal. Alternatively, if interactions are strong, or seedlings are sensitive, then seed dispersal will be relatively unimportant. Two parallel experiments, single-species seed additions and multiple-species seed additions, examine the effects on the populations and communities, respectively. Single species additions are a geometric series of five seed densities, whereas multiple species are a geometric series of five seed richnesses. Initial results indicate seedling density to be strongly controlled by seed dispersal. These effects are expected to fade, however, as the seedlings age and grow.

Mammalian Seed Predation
Together with Harald Beck, we are investigating the effects of mammals on seedling recruitment. The seed-addition experiments provide no information on the mechanisms of mortality afflicting the sown seeds. Fortunately, Harald and his collaborators constructed 40 exclosures in
1999 of varying degrees of permeability to mammals. We placed seeds of the eight focal species from the seed-addition experiment in the exclosures in April 2004, and observed their survival until January 2005, at which time almost all had germinated or died. Large seeds survived longer than small ones. Surprisingly, small mammals like spiny rats appear to have consumed more seeds than the increasingly-common herds of peccaries.

Tim Paine despues de su visita a la famosa peluquera de EBCC (?)

Contact Information

C. E. Timothy Paine
107 Life Sciences Building
Department of Biological Sciences
Louisiana State University
Baton Rouge, LA 70803