Organisms compete for biotic and abiotic factors in an ecosystem and each organism has a specific role or niche to fill in the ecosystem. What happens when the available biotic and abiotic factors available in an ecosystem change?

For example, what would happen to the finches you learned about in section two if all the cactus in a certain area died? The cactus finch would not have a food source and it would not survive. The finches that had adaptations for eating other types of food would survive, and they would live to pass on their traits to their offspring. This is known as natural selection or survival of the fittest.

Watch this video to learn more about natural selection.

It is important to remember that organisms cannot change on their own to survive in a changing environment. Organisms are born with the traits that allow them to survive or not in an environment. The organisms that have the adaptation will live and pass on their advantageous traits to their offspring.