Source dataset and code: Feeding specialization shapes functional diversity of avian assemblages along a tropical rainforest elevational gradient

Avian functional diversity in montane systems has been scrutinized by researchers seeking to uncover deterministic processes driving community assembly. However, many tropical rainforests lack fully surveyed elevational gradients that could reliably inform on functional ecology of avian assemblages. In this study, we expand global coverage of elevational trends in bird functional diversity to the third largest contiguous rainforest in the world.

We conducted point-count surveys of bird communities along a 3500-m uninterrupted elevational gradient in Papua New Guinea, sampling eight distinct elevational sites. Functional diversity indices (functional richness, evenness, and divergence) were examined using Bayesian generalized additive models after standardizing for bird species richness. Additionally, we analysed phylogenetic diversity and structure, and examined community-weighted means of functional traits, including feeding guild, morphology, and dispersal ability.

Standardized functional richness declined sharply from the lowlands to 1700 m a.s.l., followed by a weak decrease towards the treeline. Functional evenness decreased monotonically with elevation, while functional divergence increased at low elevations and again near the treeline. Phylogenetic diversity exhibited a monotonic decline accompanied by increased phylogenetic clustering at higher elevations.

The mid-elevation collapse of functional richness and divergence was likely caused by complex multi-trophic interactions. Reduced availability of large fruits contributed to declines in frugivore body size and beak dimensions, while high abundance of invertebrates led to dominance of functionally uniform insectivores. Near the treeline, bird communities displayed morphological shifts toward terrestrial lifestyles with reduced dispersal ability, suggesting environmental filtering by forest structure.

By examining trends in individual functional traits, this study highlights the role of trophic interactions in shaping avian functional diversity along an ecologically distinct rainforest system. Similar research using robust and standardized trait datasets can deepen our understanding of ecosystem functions and guide conservation strategies for different functional groups of birds across tropical regions.