Food resources shape bird assemblages, rendering trophic structure globally convergent

Rubén Bernardo-Madrid, Joaquín Calatayud, Kerry Stewart, Martin Rosvall, José Luis Tella, Chris Venditti, Luca Santini, Martina Carrete, Manuela González-Suárez

Species persist only when energy resources are available and organisms have traits to exploit them. Because resources such as fruit or carrion differ in abundance and diversity, general principles of energy flow and niche theory should shape differences in species richness among trophic guilds within assemblages. Yet, this hypothesis remains empirically untested. Here, we analyze 31,251 local bird surveys across North America and 10,753 large-scale assemblages worldwide. Within assemblages, more speciose guilds have more energy transformed into biomass, lower per-species energy demand, and greater morphological diversity associated with foraging strategies. These results help explain why, despite distinct ecological and evolutionary histories, the trophic structure of bird assemblages converges globally, suggesting that fundamental constraints related to food acquisition provide a blueprint for species assembly.