Timing matters: phenological constraints and predation shape Arctic community structure

Ecological theory predicts that abiotic constraints and biotic interactions jointly shape species assembly, yet empirical evidence for their combined effects on community structure remains limited. In Arctic ecosystems, spring snowmelt sets the timing and duration of the snow-free period, thereby controlling food availability, and predation often imposes strong additional pressure on prey species. Using a 10-year dataset on the occurrence of 11 bird species across a 600 km 2 study area, we evaluated how spring snowmelt timing and predator density influence species occurrence and community structure in the High Arctic tundra. We found that species occurrence declined with later snowmelt dates, with larger-bodied species being particularly constrained by short snow-free periods. Predation further modulated species occurrence, with responses varying according to body mass. Our findings highlight the combined influence of the phenology of food availability and predation as fundamental ecological filters shaping community structure. Building on species contrasted responses, we propose a conceptual framework for how phenological constraints and predation shape community assembly in highly seasonal environments.