Community assembly, functional traits, and phylogeny in Himalayan river birds

The rivers of the Himalaya hold the most diverse community of specialist river birds on Earth. This paper asks how that coexistence is possible: do species sort themselves by habitat, by body size and foraging style, by shared ancestry — or by all three at once?

We surveyed headwaters across more than 3,000 m of elevation in the Indian Himalaya, then combined three kinds of information in a single ordination: which species were present, what those species are like (body mass, bill, tarsus, tail, breeding strategy, foraging mode), and what the river was like where they occurred.

Three patterns emerged. Community composition turned over strongly with elevation and with how natural the river was: species that forage in the river–riparian ecotone gave way, higher up, to small insectivores that depend directly on the channel. Trait composition shifted in step, so that communities became more tightly clustered by function at high elevation — the signature of environmental filtering, where only certain kinds of birds can persist. And ancestry mattered: some traits carried a strong phylogenetic signal (body mass, bill size, tarsus length) while others did not (body size, tail length, breeding strategy).

The conclusion is that Himalayan river bird communities are assembled by a blend of evolutionary constraint and habitat filtering, with some finer niche-based sorting on top. That is also an argument for heterogeneity: the pools, riffles, gravel bars and forested banks of a mountain river are what allow so many similar birds to divide the same corridor between them.

Read it in plain words: what we found on the river birds page.

Recommended citation: Sinha, A., Chatterjee, N., Krishnamurthy, R., & Ormerod, S. J. (2022). "Community assembly, functional traits, and phylogeny in Himalayan river birds." Ecology and Evolution, 12, e9012.
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