A three year study on Daphne Major island, Galapagos, describes the ecology and morphology of a simple Geospiza community. The four part thesis discusses the breeding and feeding ecology of two Daphne finches; G. fortis is a generalist adapted to a variable environment, and G. scandens is an ecological specialist experiencing a more stable environment. The measurement, growth, allometry, and multivariate properties of seven external morphological characters are described. The repeatabilities and heritabilities of the seven characters and principal component scores are large. Relations between the unusual intermediate-sized Daphne G. fortis phenotype and the Daphne environment are examined. Four hypotheses for the intermediacy, including genetic drift, hybridization, local adaptation, and competition are suggested, with evidence found to support parts of each except genetic drift. An episode of intense directional natural selection is documented, and Lack's character release explanation of the Daphne G. fortis phenotype is revised.

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