Each organism is adapted to their environment meaning that the way they look and behave makes it suited to survive and reproduce in their habitats (has high fitness). If organism changes its environment (due to natural disaster or human influence) it must respond to this change by a process called adaptation. Adaptations can be either structural or behavioral, both in order to make organism better suited to new environment (better fitness). But, the fitness of a given organism (its trait) can also be different in different selective environments, some trait is well-adapted to one environment, but it is not in another.