Adaptive radiation refers to the process where a single ancestor species rapidly diversifies into a variety of forms that are each adapted to specific environments or ecological niches. This phenomenon typically occurs when a group of organisms encounters new and varied environments, allowing them to exploit different resources.
The reason species evolve during adaptive radiation is primarily due to the availability of ecological opportunities. For instance, when new habitats become available—after events like volcanic eruptions, glacial retreats, or the colonization of uninhabited islands—organisms can spread out and adapt to the different conditions found in these habitats.
Another factor is the absence of competition for resources. In new environments, there may be few or no predators, competitors, or diseases, allowing the species to thrive and diversify. This leads to natural selection favoring traits that are advantageous in different environments, which results in the formation of new species over time.
For example, the finches of the Galápagos Islands evolved different beak shapes and sizes to utilize various food sources available on the islands. Each beak adaptation allowed the finches to exploit different niches, leading to the emergence of several distinct species from a common ancestor.
In summary, species evolve during adaptive radiation as a response to new ecological opportunities and the need to adapt to varied environments, driven by natural selection and the absence of competition.