A general framework for species‐abundance distributions: Linking traits and dispersal to explain commonness and rarity

Species‐abundance distributions (SADs) describe the spectrum of commonness and rarity in a community. Beyond the universal observation that most species are rare and only a few common, more‐precise description of SAD shape is controversial. Furthermore, the mechanisms behind SADs and how they vary along environmental gradients remain unresolved. We lack a general, non‐neutral theory of SADs. Here, we develop a trait‐based framework, focusing on a local community coupled to the region by dispersal. The balance of immigration and exclusion determines abundances, which vary over orders‐of‐magnitude. The local trait‐abundance distribution (TAD) reflects a transformation of the regional TAD. The left‐tail of the SAD depends on scaling exponents of the exclusion function and the regional species pool. More‐complex local dynamics can lead to multimodal TADs and SADs. Connecting SADs with trait‐based ecological theory provides a way to generate more‐testable hypotheses on the controls over commonness and rarity in communities.