Data from: Trophic niche width increases with bill size variation in a generalist passerine: a test of the niche variation hypothesis

  • Chun I. Chang (Contributor)
  • Yu Cheng Hsu (Contributor)
  • Shuh J. Kao (Contributor)
  • Pei-Jen Shaner Lee (Contributor)
  • Linhua Ke (Contributor)



1. The niche variation hypothesis (NVH) predicts that populations with wider niches are phenotypically more variable than populations with narrower niches, which is frequently used to explain diversifying processes such as ecological release. However, not all empirical evidence supports the NVH. Furthermore, a relationship between population phenotypic variation and niche width can be caused by sexual selection or environmental gradients, which should be carefully considered along with competition in explaining niche variation. 2. In this study we used eight populations of a generalist passerine species, Paradoxornis webbianus (vinous-throated parrotbill), to test the NVH. We assessed evidence of ecological sexual dimorphism and environmental gradients in bill morphology of P. webbianus. A total of 170 P. webbianus from eight sites ranging 24-2,668 m in altitude were included in this study. We used two principal components to quantify bill morphology, one describes bill size and the other describe bill slenderness. We used stable carbon and nitrogen isotope values of bird feathers to quantify trophic positions, and we estimated population trophic niche width using Bayesian standardized ellipse area. 3. Paradoxornis webbianus with larger and more slender bills fed at higher trophic levels and population trophic niche width tended to increase with bill size variation, supporting the NVH. The males had larger bills and marginally higher nitrogen isotope values than the females, suggesting ecological sexual dimorphism. Despite a positive correlation between bill size and wing length indicating sexual selection for larger male size, only three of the eight populations showed both male-biased bill size and male-biased wing length. Sexual dimorphism explained 13%-64% of bill size variation across sites, suggesting its role in niche variation could vary greatly among populations. The variation in bill slenderness in P. webbianus increased with elevation. However, neither bill size variation nor trophic niche width changed with elevation. Therefore, environmental gradients that could be reflected in the elevation are not likely to drive the observed morphological and niche variation. 4. This study provides an empirical case for the NVH and highlights the importance to investigate sexual dimorphism and environmental gradients in the studies of niche dynamics.,Morphological and isotope data of the vinous-throated parrotbills in TaiwanThis file contains data on 170 individual adult Paradoxornis webbianus captured between 2009 and 2012 from eight sites in Taiwan. The columns include, from left to right: sampling data (short date format: yyyy/mm/dd), species scientific name, latitude of the site, longitude of the site, site full name in English, site short name used in the associated manuscript, tag showing the band number of the bird (a number without a beginning letter "K" indicates the bird died during handling), sex of the bird, stable carbon isotope values of the bird's feather tissue, stable nitrogen isotope values of the bird's feather tissue, altitude of the site, the bird's bill length in mm, the bird's bill width in mm, the bird's bill depth in mm, the bird's wing length in mm, and the name of the technician who performed the morphological measurements. Sex of the bird was determined by molecular sexing. Stable carbon and nitrogen isotope values were meausured on a ThermoFinnigan Delta Plus Advantage Isotope Ratio Mass Spectrometer (Bremen, Germany).Parrotbill_NVH_Hsu2013.xlsxIsotope data of plant foliar samples in TaiwanThis file contains stable carbon and nitrogen isotope data of foliar samples from 69 plants (50 unique taxa at species or genus level) collected at six sites in Taiwan. These are used to calculate baseline isotope values for the consumer species, Paradoxornis webbianus, in the associated publication. The columns are: plant species scientific name, stable carbon isotope value of the foliar tissue, stable nitrogen isotope value of the foliar tissue, elevation, latitude and longitude of the site, full name of the site and short name of the site.Plants_NVH_Shaner2013.xlsx,
Date made available2014 Mar 1
PublisherUnknown Publisher

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