Resource heterogeneity increases biological diversity by providing opportunity for niche partitioning and resource specialization. Organisms which use few of the available resource forms are considered specialists, while those which use many resource forms are considered generalists. The relative proportion of specialists and generalists within a community impacts ecosystem functions, such as total productivity. Being a resource specialist or generalist may come with a fitness cost or favor performance tradeoffs. For example, generalists may suffer a fitness cost for maintaining a broad ecological niche.Heterotrophic microbes and primary producers have the potential to specialize on different chemical forms of essential nutrients such as nitrogen and phosphorus, yet there have been few studies of nutrient specialization, limiting our understanding of associated costs or performance tradeoffs. In the present study, we quantified phosphorus resource specialization by aquatic bacterial isolates and tested for a specialization-performance tradeoff, using bacterial growth rate as the measure of performance. We found evidence for bacterial specialization on phosphorus form and for an environment-specific specialization-growth rate tradeoff. Our results indicate that nutrient-based resource specialization can strongly influence an important performance trait of an organism, but these affects may be environment-specific. Results from this study improve our understanding of how a species' niche breadth may impact its ecological strategies and competitive outcomes
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