Which of the following could be a reason for the variation in beak shapes among Galapagos Finches?

Variation in beak shapes among Galapagos Finches is primarily attributed to the geographical separation of populations. When populations are geographically isolated from one another, they experience different environmental pressures and resources. This isolation can lead to divergence, as the finches adapt to the specific food sources available in their respective environments.

For instance, finches that live in areas where seeds are hard and tough may develop stronger, thicker beaks to help them crack these seeds, whereas those in regions with softer fruits may evolve longer, narrower beaks for extracting food. Over time, these adaptations can accumulate, resulting in significant differences in beak shape among the finch populations on different islands.

The other options do not provide a compelling explanation for the diversity of beak shapes. Identical diets among different species would not drive morphological change, as they would face the same selection pressures and thus remain similar. Environmental pollution may impact populations but is less of a driving factor in the long-term evolutionary adaptations seen in these finches than natural selection based on geographic variance. Universal mating calls are related to reproductive behaviors, not directly to the physical adaptations like beak shape that occur in response to ecological niches.