Geospiza fortis, medium ground finch, and Geospiza fulginosa, small ground finch, have similar beak sizes when they do not live together. However, when they live together the beaks sizes are different. This is an example of

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Quizplus · Accepted Answer

Character displacement refers to the evolutionary divergence in morphology or behavior between sympatric (geographically overlapping) species due to competition for resources. In this case, the similar beak sizes of Geospiza fortis and Geospiza fulginosa change when they live together, indicating they are competing for resources, which has led to the divergence in beak sizes. Mutualism, commensalism, and intraspecific competition do not explain this pattern of evolutionary divergence.

Geospiza Fortis, Medium Ground Finch, and Geospiza Fulginosa, Small Ground