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.
Relationships between aspects of biodiversity, biomass, and productivity in the Luquillo Experimental Forest.
Cox, Stephen1, 2, Willig, Michael2, Scatena, Fred3, 1 2 3
ABSTRACT- Understanding the relationship between biodiversity and productivity is critical from theoretical and applied perspectives. However, few data are available which allow the direct comparison of these parameters in tropical forests. Long-term data on tropical forest dynamics collected by the U.S.D.A. Forest Service in the Luquillo Experimental Forest provide a unique opportunity to explore such relationships. We present results of an analysis of the relationship between biodiversity (i.e., species richness, and species diversity weighted by abundance and species diversity weighted by biomass), biomass (a commonly used surrogate of productivity), and productivity at two sites, Sabana 4 and Rio Grande. Despite major differences in landuse history (Sabana 4 is relatively undisturbed, whereas Rio Grande experienced culling of non-crop species in 1957), these two sites exhibit similar unimodal relationships between productivity (or biomass) and species richness. However, when indices of biodiversity are weighted by the biomass of species rather than their abundance, Sabana 4 exhibits a negative linear relationship, whereas Rio Grande exhibits a unimodal relationship. Because most of the mechanisms proposed to account for the relationship between diversity and productivity deal with the way in which resources are divided up among individuals or species, examining the relationship of productivity to the distribution of individuals, or even biomass, among species offers more insight into the mechanisms that give rise to the patterns we see in nature. In addition to changing the constituent species, anthropogenic effects at Rio Grande resulted in a redistribution of biomass among species. Nevertheless, the distribution of individuals among species remained similar to that in Sabana 4.
KEY WORDS: Biodiversity, Productivity, Biomass, Unimodal