COS 168-1 - Traits and dispersal shape Species Abundance Distributions (SADs): experimental tests of mechanistic theory

Abstract: Understanding what determines Species Abundance Distributions (SADs) in ecological communities should help predict community assembly under different conditions. We developed a mechanistic trait-based theory of community assembly that includes resource competition and immigration and is capable of making testable predictions. These predictions were tested in a controlled laboratory experiment at three temperatures and rates of immigration with phytoplankton communities with known thermal traits. The theory predicted dominance of species with thermal traits that match the temperature of each experimental treatment, while species with poorly matched thermal traits were predicted to have low abundance. Most of the predictions were confirmed, either quantitatively or qualitatively. In particular, immigration propped up species with temperature optima that deviated from the experimental temperature, while species whose traits matched the treatment remained dominant regardless of the immigration rate. At the same time, the discrepancies revealed the importance of other factors and traits not included in the model, such as nutrient utilization traits and maximum growth rates. This work demonstrates the advantages of the dynamic interplay between theory development and its rigorous testing through experiments.