PARENT SESSION
Oral Session #77: Biodiversity and Ecosystem Function II.
Presiding: G. Chong
Thursday, August 8. 9:00 AM to 11:30 AM. Coconino Meeting Room, TCC.
Loss of plant species in productive habitats is not due to seed limitation.
Stevens, Martin Henry*,1, Schnitzer, Stefan2, Bunker, Daniel3, Carson, Walter3, 1 HStevens@muohio.edu, Oxford, OH2 University of Minnesota, St. Paul, MN3 University of Pittsburgh, Pittsburgh, PA
ABSTRACT- At local and regional scales, the number of species that can coexist tends to fall in productive habitats, and ecologists don't know why. In communities where immigration contributes to the number of species present, a decline in the number of species may be due to either increased local extinction, or decreased immigration. We tested the role of immigration along a productivity gradient using an early successional plant assemblage where colonization limitation and immigration could be expected to contribute to community dynamics. In a fully crossed experimental design, we manipulated soil fertility, seed density, and plant litter to test whether a decline in the number of species in productive (fertile) habitats could be ameliorated by adding seeds with or without litter. Seed addition doubled the number of seedlings. By the end of the season, however, the seed addition had no demonstrable effect on plant density, species composition, or the number of species present at any level of fertilizer. These results indicate that immigration via seeds does not vary substantially with soil fertility and productivity, and therefore cannot explain the decline in the number of species in productive habitats. This finding is consistent with the assumption that competition among vegetative individuals plays the primary role in regulating the number of plant species along productivity gradients.
KEY WORDS: species richness, biodiversity, colonization, immigration