PARENT SESSION
Oral Session #69: Conservation: Biodiversity assessment and reserve design.
Presiding: T. Norton
Wednesday, August 7. 1:00 PM to 4:45 PM. Grand Ballroom Central, Radisson.
Species time relationships in a Kansas grassland: diversity despite dominance.
Adler, Peter*,1, Lauenroth, William1, 1 Graduate Degree Program in Ecology and, Fort Collins, CO, 80523
ABSTRACT- In 1960, Preston proposed that the relationship between time and species number should be equivalent to the relationship between area and species number, but the lack of appropriate data sets has allowed this important hypothesis to remain virtually untested. We constructed species time relationships using plant composition data from 18 permanent quadrats in western Kansas censused annually over 35 years. For each of the 18 1-m2 plots, the log of species number increased linearly with the log of time, and the slopes of these log-linear regressions ranged from 0.32 to 0.45 with a mean of 0.4. The similarity between these curves and species area relationships supports Preston's hypothesis. We used a neutral community model (NCM), a tool for understanding macroecological patterns, to help us further interpret the species time relationships in the Kansas data. The NCM generated species time curves with slopes 0.4 or greater when the potential number of species in the community was greater than the number of individuals. However, when these parameters were used in a grid of interacting neutral communities, reproducing the observed species time relationship, the accompanying species area curve was unreasonably steep (slopes approached 1). The distribution of species' frequencies through time and space revealed far more pronounced dominance in the Kansas community than in the simulated one. In this grassland, species accumulated rapidly through time despite extreme dominance by a few species. We discuss the implications of this paradox from both theoretical and management perspectives.
KEY WORDS: diversity, species-area, species-time, neutral community model