Abstract
Darwin’s finches are a classic example of adaptive radiation involving differential use of dietary resources among sympatric species. Here, we apply stable isotope (δ13C, δ15N, and δ2H) analyses of feathers to examine ecological segregation among eight Darwin’s finch species in Santa Cruz Island, Galápagos collected from live birds and museum specimens (1962–2019). We found that δ13C values were higher for the granivorous and herbivorous foraging guilds, and lower for the insectivorous finches. Values of δ15N were similar among foraging guilds but values of δ2H were higher for insectivores, followed by granivores, and lowest for herbivores. The herbivorous guild generally occupied the largest isotopic standard ellipse areas for all isotopic combinations and the insectivorous guild the smallest. Values of δ2H provided better trophic discrimination than those of δ15N possibly due to confounding influences of agricultural inputs of nitrogen. Segregation among guilds was enhanced by portraying guilds in three-dimensional isotope (δ13C, δ15N, and δ2H) space. Values of δ13C and δ15N were higher for feathers of museum specimens than for live birds. We provide evidence that Darwin’s finches on Santa Cruz Island tend to be generalists with overlapping isotopic niches and suggest that dietary overlap may also be more considerable than previously thought.
Highlights
Introduction published maps and institutional affilDarwin’s finches of the Galápagos Islands are a classic example of adaptive radiation and ecological segregation [1,2]
Values of δ13 C were lowest for Green Warbler Finch (GWF), highest for Cactus Finch (CF) and Small Ground Finch (SGF), and intermediate for Medium Ground Finch (MGF), Large Ground Finch (LGF), Small Tree Finch (STF) and Woodpecker Finch (WF)
Foraging guilds differed for all isotopes, whereby the insectivorous guild had the lowest δ13 C values and highest δ15 N and δ2 H values (Table 1)
Summary
Darwin’s finches of the Galápagos Islands are a classic example of adaptive radiation and ecological segregation [1,2]. Ground finches (Geospiza spp.) feed primarily on seeds, while tree finches (Camarhynchus spp.) feed on fruits and arthropods in trees, the single vegetarian finch (Platyspiza crassirostris) on leaves and fruits, and warbler finches (Certhidea spp.) on arthropods [1,6]. These differences in diet are famously associated with differences in beak size and shape. Ground finches represent an adaptive radiation, where they may be characterized as being ‘imperfect iations
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