Since early in the history of ecology, ecologists have sought to understand the mechanism underlying species abundance distributions (SADs) but there is not yet an obvious tractable path from individual performance to community patterns. We used 22 phytoplankton species from various optimum growth temperature ranges, and performed dynamic models and controlled experiments to evaluate the effect of temperatures and immigration on the shapes of SADs. We found that SADs were shaped by species traits and their associations with environments, and immigration. Abundant species were those with traits matching the environment. Immigration allowed species with unsuitable traits to persist, which makes communities with a few common species and many rare species. Abundances of common species were independent of immigration, but abundances of rare species were proportional to it. Our study suggests that empirical macroecological patterns can be reproduced from microscopic processes such as individual growth and resource use, and their associations with environments, and immigration.