Final answer:
Birds with beaks that are not ideal for their diets being out-reproduced by those with ideal-sized beaks is an example of natural selection. The studies on Darwin's finches by the Grants illustrate this, where finch populations evolved beak sizes better suited to the available food sources, showing differential reproduction and evolution in action.
Step-by-step explanation:
The scenario where birds with beaks that are larger or smaller than required by their diet are out-reproduced by birds with ideal-sized beaks is an example of natural selection. This process entails better-adapted organisms surviving and reproducing at higher rates. Darwin's finches are a classic example of this phenomenon, where finches with beak sizes that are more adapted to available food sources are more likely to survive and produce offspring. During the Galápagos finches study conducted by Peter and Rosemary Grant, it was observed that finch beak sizes evolved in response to the types of seeds that were available due to environmental changes, such as droughts and rainy periods.
For instance, during a drought, finches with larger and broader beaks could eat a wider variety of seeds, including those that were harder to crack, giving them a survival advantage. This led to an increase in average beak size in subsequent generations. Such differential reproduction reinforces how natural selection can drive the evolution of species over time.