Amazonian hyperdominance exceeds expectations of neutral theory

Hyperdominant species are those that account for 50% of individuals at a given scale, and this community characteristic has been highlighted for tree species in the Amazon basin because a particularly small proportion of highly abundant species make up a majority of individuals. It has not been well‐established, however, if Amazon‐wide hyperdominance is more substantial than expected under demographic stochasticity among equal competitors because carrying out a test of neutral predictions at such a large‐scale is challenging in part due to the complex and uncertain task of effectively considering dispersal limitation. Here, we circumvent this challenge by first comparing Amazon‐wide data to the simpler global dispersal neutral model, then demonstrating that this constitutes a conservative test of hyperdominance in that a dispersal‐limited model only decreases neutral‐predicted hyperdominance, even combined with aggregated sampling. Importantly, we also demonstrate that the data falls outside of neutral‐predicted variation in proportion of hyperdominant species and species abundances, rather than relying on standard statistical tests whose assumptions are not satisfied. This enables us to demarcate tree species more dominant than neutral expectations. We additionally demonstrate that alternative modes of speciation to the standard point mutation model of neutral theory do not enable it to both better predict hyperdominance and provide a good fit to the species abundance distribution as a whole. Finally, we show higher than predicted abundances of dominant species to be robust to reductions in observed abundance representing taxonomic uncertainty. Synthesis : Our work robustly demonstrates hyperdominance necessitating deterministic explanation at the Amazon‐wide scale and lays out a tractable approach to test for such hyperdominance at large scales that can be used in other systems.