Bite performance and morphology in a population of Darwin’s finches: implications for the evolution of beak shape. Journal of Evolutionary Biology 18:669-675. Evolution of bite force in Darwin’s finches: a key role for head width. Possible human impacts on adaptive radiation: beak size bimodality in Darwin’s finches. Reproductive isolation of sympatric morphs in a population of Darwin’s finches. Journal of Evolutionary Biology 21:263-275. A geometric morphometric appraisal of beak shape in Darwin’s finches. Force-velocity trade-off in Darwin’s finch jaw function: a biomechanical basis for ecological speciation? Functional Ecology 23:119-125. Disruptive selection in a bimodal population of Darwin’s finches. Philosophical Transactions of the Royal Society. Divergence with gene flow as facilitated by ecological differences: within-island variation in Darwin’s finches. Exploring possible human influences on the evolution of Darwin’s finches. Evolutionary Ecology Research 14:365-380. Individual specialization and the seeds of adaptive radiation in Darwin’s finches. Journal of Evolutionary Biology 27:1093-1104. Darwin’s finches and their diet niches: the sympatric co-existence of imperfect generalists. Genomic variation at the tips of the adaptive radiation of Darwin’s finches. Habitat filtering not dispersal limitation shapes oceanic island floras: species assembly of the Galápagos archipelago. Urbanization erodes niche segregation in Darwin’s finches. Temporally varying disruptive selection in the medium ground finch ( Geospiza fortis). The ecology and evolution of seed predation by Darwin’s finches on Tribulus cistoides in the Galápagos Islands. Where did the finch go? Insights from radio telemetry of the medium ground finch ( Geospiza fortis). The terroir of the finch: how spatial and temporal variation shapes phenotypic traits in Darwin’s finches. Phenotypic divergence of traits that mediate antagonistic and mutualistic interactions between island and continental populations of the tropical plant, Tribulus cistoides (Zygophyllaceae). The fitness landscape of a community of Darwin’s finches. The Living Dead: Darwin's finches and Museums.The adaptive radiation of Darwin's finches.Most recently, we are starting intensive effort to understand how finch evolution influences plant communities in Galapagos. This improved fitness of intermediate forms thus breaks one of the barriers keeping different beak sizes as separate gene pools – in essence halting or reversing speciation. We suggest that this change is the result of the introduction of plants and the feeding of finches, both of which may reduce selection against intermediate beak sizes. This suggests that humans alter food resource distributions in ways that reverse the process of speciation and cause incipient species to fuse back together. We have also found that a formerly bimodal population of finches has lost this property in concert with an increase in human population size at Academy Bay on Santa Cruz Island. We are also asking whether this adaptive split has led to assortative mating, reductions in gene flow, and the onset of speciation. Part of our work is focused on determining whether large- and small-beaked morphs do indeed specialize on different foods (i.e., divergent selection). These sympatric beak-size morphs within species are thus a small-scale version of the differences among established species, suggesting that the morphs can be used to understand the early stages of adaptive radiation. These two morphs have probably arisen because two different resources are available: hard seeds, for which large beaks are most appropriate, and soft seeds, for which small beaks are most appropriate. Specifically, some populations of finches within a species have bimodal beak size distributions, with one mode composed of a small-beaked morph (left side of the photo) and the other of a large-beaked morph (right side of the photo). Some of our work in Galapagos focuses on the early stages of adaptive radiation.
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