Wednesday, June 6, 2007 - 1:30 PM
260

Species Cell Size And Distribution Jointly And Differentially Determine Diatom Population Densities In US Running Waters

Sophia I. Passy, University of Texas at Arlington, Arlington, TX 76019

Among the most studied relationships in ecology are those of population density with 1) body size and 2) species distribution. Traditionally, these two relationships have been examined separately. Here, I explored how diatom density was controlled by cell size (biovolume) and species distribution in benthic and planktonic stream habitats all the way from individual localities and watersheds to the entire US. At all scales, density was predominantly a negative function of biovolume and a positive function of distribution. Partial regressions revealed that biovolume, by itself, explained substantially higher percentage of the variance in density at local than at regional and continental scales. Conversely, species distribution was a much more important descriptor of density at larger scales and a slightly better predictor than biovolume at local scales. At large scales density was governed primarily by distribution, to a lesser extent and only in the benthos by the covariance of distribution and biovolume, whereas biovolume was a marginal predictor in all habitats. This discovery suggests that the strong relationships between density and body size, reported for populations ranging from unicellular algae to mammals, may be less direct than previously thought but mediated by large scale species distributions.

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