Practise AP Biology 7.2.A questions by interpreting phenotypic variation and predicting how environmental pressures change fitness and trait frequencies.
In 1981 a single immature male Geospiza conirostris finch flew more than 100 kilometers from the Galápagos island of Española to the Galápagos island of Daphne Major, where no G. conirostris finches were living. The immigrant finch bred with a female G. fortis, a species of finch common on Daphne Major. The finches and later generations interbred only within their lineage. By 2012 scientists counted 23 individuals, including eight breeding pairs, within this hybrid lineage on Daphne Major. The hybrid lineage became known as Big Bird.
Birds with different beak shapes and sizes eat different types of food. The dimensions of the Big Bird beaks relative to the beaks of the major competitor finch species on Daphne Major are shown in Figure 1.
Figure 1. The dimensions of the beaks of the Big Bird lineage and of its major competitor species in 2012 on Daphne Major. Each symbol represents the beak dimensions of a single bird.
Based on the data in Figure 1, explain why the Big Bird population has been able to survive and reproduce on Daphne Major.
A virus infects and kills all G. magnirostris on Daphne Major but does not affect the other finch species. Assuming food type and availability stay the same, predict the most likely change in the beak phenotype of the Big Bird population after six more generations.