Foraging behavior, not prey identity, facilitates niche packing in a tropical montane avifauna

Understanding the mechanisms of key ecological and evolutionary patterns and the restructuring of biodiversity in the Anthropocene is contingent on filling knowledge gaps about resource consumption across trophic levels and how resource use is limited by factors intrinsic to organisms and extrinsic aspects of the environment across deep and shallow timespans. We quantified diet composition and foraging behavior across a community of invertivorous birds in the Ecuadorian Andes to explore how resource use facilitates the packing and expansion of niche space across an elevational gradient, contributing the tropical Andes status as the most species-rich region on earth. We found evidence that niche packing of morphologically similar species may be offset by greater behavioral plasticity in foraging behavior at species-rich lower elevations where competition is likely more intense and invertebrate prey more diverse. We also tested the extent to which the breadth and similarity of birds foraging and dietary niches are shaped by the environmental and competitive gradient across elevation versus species identity and phylogenetic similarity. The specific behaviors and substrates that birds used were far more strongly associated with species identity than elevation, particularly for behaviors requiring specialized morphology that is phylogenetically conserved. In contrast, species identity had little effect on prey selection, which was more strongly associated with elevation. Our findings suggest that elevational range dynamics and niche packing of tropical montane birds are more strongly shaped by phylogenetic constraints on foraging behavior than by specializing on specific prey taxa, highlighting the importance of maintaining structural integrity in tropical forests for preserving functional diversity.