Final answer:
The average beak depth in the finch population during the drought increased due to natural selection, where finches with bigger beaks survived due to their ability to eat the more abundant large seeds, leading to a genetic shift towards larger beak sizes in subsequent generations.
Step-by-step explanation:
The increase in the average beak depth of finches during the drought is attributed to the concept of natural selection. Due to the scarcity of small seeds, finches with smaller beaks struggled to survive as they were unable to crack open the large hard seeds that became more common. In contrast, finches with larger and broader beaks could easily access food resources, leading to their survival and reproduction. This resulted in an elevated average beak size within the finch population.
Furthermore, as substantial documentation by Peter and Rosemary Grant has shown, these physical changes happened from one generation to the next and were passed down genetically. The surviving large-beaked birds reproduced, and this selective breeding process favored offspring with similar beak characteristics. Consequently, the population evolved to have larger bills suitable for the available food sources during the drought.
Predictions for the finch population under continuous drought and isolation suggest that the trait for larger beaks will become more prevalent, leading to an overall evolutionary shift in the population towards larger beak sizes. This exemplifies evolution by natural selection in response to environmental pressures.
The increase in average beak depth during the drought was caused by natural selection. The drought resulted in a scarcity of small seeds with thin shells, making it difficult for birds with small beaks to find food. However, birds with larger beaks could still crack and eat the larger seeds available. As a result, the small-beaked birds died off, while the birds with larger beaks survived and reproduced. This led to an increase in the average beak depth in the finch population.