PARENT SESSION
Oral Session #40: Biodiversity and Ecosystem Function: Do species and species richness matter?. Presiding: R. Dirzo.
Wednesday, August 8, 2001. 8:00 AM to 12:00 PM. Madison Ballroom D.

Limitations on species richness along a grassland productivity gradient: the importance of species availability.

Foster, Bryan¹, ¹

ABSTRACT- A major goal in ecology is to discern under what habitat conditions species diversity is limited by local ecological interactions and under what conditions diversity is limited by the richness of the species pool. I will present results from the first year of a propagule addition experiment designed to assess the relative importance of local processes and seed availability in governing colonization and small-scale plant species richness across a natural gradient of productivity. Forty clusters of four, 1x1 m plots were established along a topographic-productivity gradient in successional grassland at the Nelson Environmental Studies Area (Univ. of Kansas). To each cluster, a 2x2 factorial arrangement of treatments was applied: two levels of seed addition of 34 grassland species selected from the regional pool (no seed added; seed added); and two levels of disturbance designed to disrupt the canopy and alter micro-site availability (not disturbed; disturbed). Species richness declined monotonically with increasing productivity in all treatments. In the undisturbed treatments, the addition of seeds strongly increased seedling recruitment and richness in low productivity sites, an effect that declined in magnitude with increasing productivity. However, in disturbed treatments, the addition of seeds increased recruitment and richness at all levels of productivity. The results support the hypothesis that the relative importance of local processes and species availability in limiting colonization and small-scale species richness varies with productivity.

KEY WORDS: colonization, productivity, species availability, species richness