For 600m years, life has been responding to our changing world. Virtually every conceivable environment in every corner of the planet has been occupied as animals and plants have diversified. Environmental shifts and mass extinctions produce new evolutionary opportunities for organisms to exploit as they compete for survival.
But how do organisms grasp these opportunities? Do they evolve new traits in response to the pressures of new environments, or are they able to move into new habitats because they have already evolved the right adaptations? Much of evolutionary study rests on the the former idea being right. Yet a new study of the development of horses is the latest in a growing body of research that suggests the answer to this chicken-egg situation may be more complicated.
The chances of an organism’s survival in a new habitat are governed by the area’s biological and environmental conditions and whether these are compatible with the organism’s basic requirements (its ecological niche). If they are compatible, the organism may be able to persist, adapt and thrive. The more specialised an organism’s ecological niche, the harder it may be to move into a new environment.
For example, the caterpillars of the monarch butterfly feed almost exclusively on milkweed. It’s hard to imagine the caterpillars successfully colonising a new habitat that doesn’t have this vital food source. Another point to consider is that just because an organism can survive in a new environment doesn’t necessarily mean it will be able to get there. For example, it would be practically impossible for polar bears to naturally spread from the North Pole to Antarctica.
Much of our understanding of how organisms evolve new traits to occupy new environments and ecological niches comes from the study of adaptive radiations. An adaptive radiation is the evolutionary process by which organisms rapidly diverge from a common ancestor into multiple different forms. There are numerous charismatic examples documented, including: Darwin’s finches on the Galapogos Islands, cichlid fish in the lakes of East Africa, and Anolis lizards on the Caribbean islands.