A test for community saturation along the Himalayan bird diversity gradient, based on within-species geographical variation.
The idea that ecological communities are unsaturated is central to many explanations for regional gradients in species diversity. We describe a test for differing degrees of saturation across a regional diversity gradient, based on within-species geographical variation in ecological attributes. If communities in species-poor regions are less saturated than communities in species-rich regions, species that straddle both regions should have broader niches in species-poor regions, exploiting resources that are consumed by other species in species-rich regions. We studied 10 species of Old World leaf warblers that range across the Himalayas. Elevational range and feeding method showed niche contractions in the species-poor north-west Himalayas with respect to the species-rich south-east Himalayas, whereas prey size did not vary geographically. Niche contractions are contrary to the expectation of character release in depauperate environments, as has been shown, for example in mainland-island comparisons. We show that arthropod abundances are likely a limiting resource, and that niche contractions are consistent with measurements of a narrowing of resource availability. Results suggest that north-western warbler communities are at least as saturated as the south-east and that lower resource diversity drives reduced species numbers.
Wildlife Institute of India, PO Box 18, Chandrabani, Dehradun, 248001, India.
Mousumi
M
Ghosh-Harihar
Department of Ecology and Evolution, University of Chicago, Chicago, IL, 60637, USA.
Trevor D
TD
Price
D000818:Animals; D058448:Biota; D017753:Ecosystem; D020387:Food Chain; D005843:Geography; D007194:India; D020308:Songbirds / Q000502:physiology*
Phylloscopus; Seicercus; community saturation; elevational range; foraging; generalists; latitudinal gradient; specialists