Abstract
The partitioning of biomass among genera within phytoplankton communities was compared for 165 lakes in Florida. The lakes, which differed widely in trophic status, were sampled twice between the spring and summer of 1980. The phytoplankton communities examined ranged widely in biomass and biomass partitioning, from communities with biomass distributed evenly among taxa to communities where one or a few species comprised >90% of the biomass. The number of taxa present in each of the communities increased significantly as biomass increased from <10 genera in sparse communities to >30 genera in dense (>10 mg/L) communities. There was, however, a tendency toward decreasing taxonomic richness in very dense communities. Strong positive relationships between both the coefficient of variation and the skewness of the percentage biomass distribution across taxa and total community biomass were found. The distribution of biomass within the communities changed from a relatively balanced biomass distribution across taxa at low biomass, to highly hierarchical communities, where the bulk of taxa have very small (<0.1%) biomasses and one or a few species predominate, at high biomass. This pattern of biomass partitioning suggests that interference among co-existing phytoplankton taxa increases as community biomass increases, and provides additional evidence for the biomass-dependence of phytoplankton community structure. (MacKeen-PTT)