Intraspecific trait variation shapes macro-scale patterns of niche breadth and range size

Morphological variation within species may promote adaptation across ecological and geographic space, perhaps reflecting evolutionary plasticity and adaptability. Based on this concept, species with greater intraspecific variation in morphological traits may be expected to occupy broader ecological niches and larger geographic ranges. However, even in the age of global trait datasets, intraspecific morphological variation remains poorly quantified at broad taxonomic and geographic scales, limiting our understanding of how trait flexibility shapes ecological and biogeographic patterns. Focusing on 161 species of bulbuls, a widespread avian family containing some of the most abundant bird species in the world, along with some of the rarest and most restricted in range, we conducted global-scale sampling of morphological traits. These included beak shape, tarsus length and wing length, associated with dietary niche, foraging strategy and dispersal, respectively. Using phylogenetic models, we tested whether ecological niche breadth and geographical range size are predicted by intraspecific morphological variation quantified from 8,251 museum specimens and 5,627 live captures. Our results demonstrate that morphological trait variation predicts both ecological niche breadth and geographic range size. Furthermore, widespread species exhibit greater morphological variation than restricted-range species even when comparisons are constrained to equivalent geographic extents, consistent with the hypothesis that intraspecific trait variation facilitates range expansion rather than simply accumulating as a consequence of occupying a larger range. These results identify intraspecific morphological variation as a potentially important, yet largely overlooked, predictor of ecological traits and biogeographic distributions in birds.

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Publication Details

Journal
bioRxiv (Cold Spring Harbor Laboratory)
Published
2026-11-03
DOI
https://doi.org/10.64898/2026.10.31.763334
Primary Topic
Avian ecology and behavior
Type
preprint
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preprint

Intraspecific trait variation shapes macro-scale patterns of niche breadth and range size

Olivier S. G. Pauwels, Nihan Dilşad Dağtaş, Billi A. Krochuk, Camila G. Meneses et al.
bioRxiv (Cold Spring Harbor Laboratory)
Avian ecology and behavior
preprint

Intraspecific trait variation shapes macro-scale patterns of niche breadth and range size

Olivier S. G. Pauwels, Nihan Dilşad Dağtaş, Billi A. Krochuk, Camila G. Meneses, Klara E. Widrig, Peter A. Hosner, Florante Cruz, Sontaya Manawattana, Charlotte M. Probst, WORAPHOT BUNKHWAMDI, Amancio Motove Etingüe, Kier Mitchel E. Pitogo, Daphawan Khamcha, Juan Carlos T. Gonzalez, René‐Marie Lafontaine, Malcolm C. K. Soh, Kyle D. Kittelberger, David Vander Pluym, Alfredo Sánchez‐Tójar, Carla J. du Toit, Luke L. Powell, Kwanye Zira Bitrus, Jarome R. Ali, Martin Hromada, Stephanie Chia, Vanya G. Rohwer, Hari Basnet, Martin Bulla, Lukas J. Musher, Kristof Zyskowski, Frane Babarović, Elizabeth M. Steell, Michaël P. J. Nicolaï, Kelvin S.‐H. Peh, Brian C. Weeks, Peter Mikula, Mohammad Irham, Wangworn Sankamethawee, Chima J. Nwaogu, V. V. Robin, Joseph A. Tobias, Andrew J. Pierce, Philip D. Round, Yue Wu, Ekadh Ranganathan, Susana Lin Mufumu, Caroline Dingle, James Andro Villamin, Maarten J K Hoepel, Sandupama Madhuhansi, Silvestre N.E. Malanza, Rina R.B. Perez, Graciela D. Lorenzana, Isabella C. Enriquez, Marianne L.K.Z. Fabella, Charlene R. Bajamunde, Jestonie H. Namion, Panagiotis Nikolaou, Anna M.B. Halili, Vedant Gattani, Rolly C. Urizza
preprint en

Abstract

Morphological variation within species may promote adaptation across ecological and geographic space, perhaps reflecting evolutionary plasticity and adaptability. Based on this concept, species with greater intraspecific variation in morphological traits may be expected to occupy broader ecological niches and larger geographic ranges. However, even in the age of global trait datasets, intraspecific morphological variation remains poorly quantified at broad taxonomic and geographic scales, limiting our understanding of how trait flexibility shapes ecological and biogeographic patterns. Focusing on 161 species of bulbuls, a widespread avian family containing some of the most abundant bird species in the world, along with some of the rarest and most restricted in range, we conducted global-scale sampling of morphological traits. These included beak shape, tarsus length and wing length, associated with dietary niche, foraging strategy and dispersal, respectively. Using phylogenetic models, we tested whether ecological niche breadth and geographical range size are predicted by intraspecific morphological variation quantified from 8,251 museum specimens and 5,627 live captures. Our results demonstrate that morphological trait variation predicts both ecological niche breadth and geographic range size. Furthermore, widespread species exhibit greater morphological variation than restricted-range species even when comparisons are constrained to equivalent geographic extents, consistent with the hypothesis that intraspecific trait variation facilitates range expansion rather than simply accumulating as a consequence of occupying a larger range. These results identify intraspecific morphological variation as a potentially important, yet largely overlooked, predictor of ecological traits and biogeographic distributions in birds.

bioRxiv (Cold Spring Harbor Laboratory)
University of the Philippines Los Baños (PH), University of Copenhagen (DK), HOGENT University of Applied Sciences and Arts (BE), Naturalis Biodiversity Center (NL), National Museum of the Philippines (PH), National Parks Board (SG), Houston Museum of Natural Science (US), American Museum of Natural History (US), National Museum of Natural History (US), University of Kansas (US), African Institute for Mathematical Sciences (ZA), Sun Yat-sen University (CN), Tel Aviv University (IL), University of Prešov (SK), Khon Kaen University (TH), Universidade do Porto (PT), University of Toronto (CA), Capilano University (CA), Cornell University (US), Czech University of Life Sciences Prague (CZ), University of Cambridge (GB), Mahidol University (TH), University of Michigan (US), Institute of Natural Sciences (BE), Ghent University Hospital (BE), Ghent University (BE), Bridge University (SS), Robert S. Peabody Museum of Archaeology (US), Indian Institute of Science Education and Research, Tirupati (IN), University of Southampton (GB), Natural History Museum of Denmark (DK), Imperial College London (GB), Chiang Mai University (TH), New York University (US), King Mongkut's University of Technology Thonburi (TH), University of Maryland, College Park (US), Drexel University (US), University of Coimbra (PT), University of Glasgow (GB), University of Colombo (LK)
Avian ecology and behavior
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