Darwin discovered twenty different species of finches in the galapagos islands. he hypothesized that as new islands arose, finches colonized the islands and rapidly changed into new species, depending on what food was available on each new island. the rapid formation of many new species, as in this case, is called

Adaptive radiation

Explanation:

Adaptive radiation is the evolutionary process that results in the emergence of different species from the same common ancestor, as reported in the above question. This process begins with the colonization of a particular group in a new environment, and is therefore subjected to new environmental conditions that will select the most able to survive in that particular environment.

Adaptive radiation is characterized by the formation of species in a short period of time, after the separation of groups within the same population that, over time, occupies different ecological niches and adaptive processes to survive in this new niche.

littering streams           is the answer