Because of prolonged drought, the trees on an island are producing nuts that are much smaller with thicker and harder shells. what will happen to the birds that depend on the nuts for food?

The above example illustrates evolutionary adaptation. 

This is a phenotypic or versatile characteristic, with a practical part in every individual creature, that is kept up and has been advanced by common determination. Living beings confront a progression of ecological difficulties as they develop, and demonstrate versatile pliancy as attributes create because of the forced conditions.

Size and shape of continents