Differences in species growth rates in different nutrient conditions were used to test the hypothesis that there are tradeoffs in species abilities to use different resources. Multiple species diatom communities were developed on clay tiles in incubation chambers supplied with flowing water to simulate stream conditions. A 3 x 2 factorial experiment was conducted to determine the independent and interactive effects of additions of NH3, NO3, and PO4 on species growth rates. Growth rates of most species were significantly affected by PO4 enrichment. Growth rates of Fragilaria crotonensis and Synedra ulna were independently limited by NH3, NO3, and PO4. In general, the species that had the fastest growthh rates in low nutrient regime also grew fastest in the high nutrient regime. Also, the same species had the fastest growth rates in high NH3, NO3, and PO4 concentrations. There was little evidence of adaptive tradeoffs and that competition was a dominant force in natural selection of diatoms in streams.