Black-bellied seedcrackers have either small beaks (better for eating soft seeds) or large beaks (better for hard seeds). there are no seeds of intermediate hardness; therefore, which kind of selection acts on beak size in seedcrackers

The answer is Disruptive Selection.

Explanation:

The Disruptive Selection is defined as "the situation where the selection trait is against the individual in the middle of the trait spectrum.". In the given example, there are no suitable seeds for the seedcrackers with medium sized beaks. So the criteria for the selection which is the beak size in black-bellied seedcrackers is on the different ends of the spectrum. The beaks are either small, or large. Which means that the selection trait affects the seedcrackers in the middle of the trait distribution. Therefore the answer is Disruptive Selection.

disruptive selection

Explanation:

disruptive selection causes both extreme phenotypes to be favored over the intermediate phenotypes.

this is a good question! i'll do some research and come back when i have the answer!