It is tempting to think that plants produce fruit for our pleasure and that of other creatures. They do want us to eat them, but they have an ulterior motive of getting their seeds carried away from the parent plant so the baby plants have a better chance of survival.
If all fruits that a parent plant produces were to simply all to the ground, it is unlikely that many would survive. The adult plant already has a claim on the available sunshine, soil, water and nutrients needed for plant growth. Since plants are not mobile, they must use other means to get their seeds dispersed and thus continue the species. Many do it by bribery, providing a tasty food source that a mobile beast eats and then moves on. The hard seeds inside of fruit pass through the animal’s gut undigested, and eventually get deposited somewhere with fertilizer to boot.
To assure that they are seen for consumption, many plants display what is called “pre-ripening fruit flags”, going through a series of color changes as they ripen. Fruits like blueberries, cherries, mulberries, blackberries, and raspberries all start out a green color. As they mature they turn a pink to red, then purple, black, or blue when fully ripe. This color change may serve as a signal to animals that fruit is about to ripen, encouraging them to stay in the area and feed. This ups the chances of getting the seeds dispersed.
Another trick some fruiting plants use is to go through a very early leaf color change in the fall. The bright red or yellow leaves are very distinct against a predominantly green background, and are thus attractive to animals (especially flying birds) from a distance. This early flush of color is called “foliar fruit flags”, and is used by Poison Ivy, Virginia Creeper, Sassafras, Blackgum, Wild Grapes, Dogwood, and Spice Bush to announce ripe or near ripe fruit.
The next time you enjoy wild fruit of some kind, keep in mind you are being conned, but in this case both sides win.