Niche filling slows the diversification of Himalayan songbirds

• Published in: Nature Vol. 509; no. 7499; pp. 222 - 225
• Main Authors: Price, Trevor D., Hooper, Daniel M., Buchanan, Caitlyn D., Johansson, Ulf S., Tietze, D. Thomas, Alström, Per, Olsson, Urban, Ghosh-Harihar, Mousumi, Ishtiaq, Farah, Gupta, Sandeep K., Martens, Jochen, Harr, Bettina, Singh, Pratap, Mohan, Dhananjai
• Format: Journal Article Publication
• Language: English
• Published: London Nature Publishing Group UK 08.05.2014; Nature Publishing Group
• Subjects: 631/181/759/2467; ADAPTIVE; Altitude; Animal behavior; Animals; Bioinformatics and Systems Biology; Bioinformatik och systembiologi; Birds; Body Size; China; Competition; DIVERSITY; Earth and Related Environmental Sciences; ECOLOGICAL OPPORTUNITY; Ecology; Ecosystem; Ecosystems and species history; Ekologi; Ekosystem och arthistoria; ELEVATIONAL GRADIENT; Evolution; Evolutionary Biology; Evolutionsbiologi; Genetic diversity; Genetic Speciation; Genetics; Genetik; Geovetenskap och miljövetenskap; Humanities and Social Sciences; India; LATITUDINAL GRADIENT; letter; MOLECULAR CLOCK; multidisciplinary; Niches; Origin of species; PASSERINE BIRDS; Phylogeny; PLANT-SPECIES RICHNESS; RADIATIONS; RANGE LIMITS; Reproduction; Resource availability; Science; Songbirds; Songbirds - anatomy & histology; Songbirds - classification; Songbirds - physiology; Speciation; Tibet; WORLD LEAF WARBLERS; Zoologi; Zoological research; Zoology; Tibet; China; India
• ISSN: 0028-0836; 1476-4687; 1476-4687
• DOI: 10.1038/nature13272

In Himalayan songbirds, the speciation rate is ultimately set by ecological competition, rather than by the rate of acquisition of reproductive isolation. New species need new niches The beginnings of adaptive radiation and speciation have been widely studied — in Darwin's finches, sticklebacks and cichlid fish, for example — but relatively little is known about what happens next. Specifically, what is the rate-limiting step for the establishment of new species? This seven-year study of the 358 songbird species found on the Himalayan slopes suggests that it is the rates at which new niches are created and occupied that limits diversification, not the rate at which new species form through reproductive isolation. Speciation generally involves a three-step process—range expansion, range fragmentation and the development of reproductive isolation between spatially separated populations 1 , 2 . Speciation relies on cycling through these three steps and each may limit the rate at which new species form 1 , 3 . We estimate phylogenetic relationships among all Himalayan songbirds to ask whether the development of reproductive isolation and ecological competition, both factors that limit range expansions 4 , set an ultimate limit on speciation. Based on a phylogeny for all 358 species distributed along the eastern elevational gradient, here we show that body size and shape differences evolved early in the radiation, with the elevational band occupied by a species evolving later. These results are consistent with competition for niche space limiting species accumulation 5 . Even the elevation dimension seems to be approaching ecological saturation, because the closest relatives both inside the assemblage and elsewhere in the Himalayas are on average separated by more than five million years, which is longer than it generally takes for reproductive isolation to be completed 2 , 3 , 6 ; also, elevational distributions are well explained by resource availability, notably the abundance of arthropods, and not by differences in diversification rates in different elevational zones. Our results imply that speciation rate is ultimately set by niche filling (that is, ecological competition for resources), rather than by the rate of acquisition of reproductive isolation.