Morphological shifts in island-dwelling birds: The roles of generalist foraging and niche expansion

Scott, S. N., Clegg, S. M., Blomberg, S. P., Kikkawa, J. and Owens, I. P. (2003) Morphological shifts in island-dwelling birds: The roles of generalist foraging and niche expansion. Evolution, 57 9: 2147-2156. doi:10.1554/03-021


Author Scott, S. N.
Clegg, S. M.
Blomberg, S. P.
Kikkawa, J.
Owens, I. P.
Title Morphological shifts in island-dwelling birds: The roles of generalist foraging and niche expansion
Journal name Evolution   Check publisher's open access policy
ISSN 0014-3820
1558-5646
Publication date 2003-09-01
Sub-type Article (original research)
DOI 10.1554/03-021
Volume 57
Issue 9
Start page 2147
End page 2156
Total pages 10
Editor Nicholas Barton
Mark D. Rausher
Place of publication Oxford, United Kingdom
Publisher Wiley-Blackwell Publishing
Collection year 2003
Language eng
Subject C1
270799 Ecology and Evolution not elsewhere classified
779903 Living resources (flora and fauna)
0603 Evolutionary Biology
Abstract Passerine birds living on islands are usually larger than their mainland counterparts, in terms of both body size and bill size. One explanation for this island rule is that shifts in morphology are an adaptation to facilitate ecological niche expansion. In insular passerines, for instance, increased bill size may facilitate generalist foraging because it allows access to a broader range of feeding niches. Here we use morphologically and ecologically divergent races of white-eyes (Zosteropidae) to test three predictions of this explanation: (1) island populations show a wider feeding niche than mainland populations; (2) island-dwelling populations are made up of individual generalists; and (3) within insular populations there is a positive association between size and degree of foraging generalism. Our results provide only partial support for the traditional explanation. In agreement with the core prediction, island populations of white-eye do consistently display a wider feeding niche than comparative mainland populations. However, observations of individually marked birds reveal that island-dwelling individuals are actually more specialized than expected by chance. Additionally, neither large body size nor large bill size are associated with generalist foraging behavior per se. These latter results remained consistent whether we base our tests on natural foraging behavior or on observations at an experimental tree, and whether we use data from single or multiple cohorts. Taken together, our results suggest that generalist foraging and niche expansion are not the full explanation for morphological shifts in island-dwelling white-eyes. Hence, we review briefly five alternative explanations for morphological divergence in insular populations: environmental determination of morphology, reduced predation pressure, physiological optimization, limited dispersal, and intraspecific dominance.
Keyword Niche
Zosterops
Foraging
Generalism
Islands
Morphology
Q-Index Code C1

 
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Created: Wed, 15 Aug 2007, 05:14:16 EST