Final answer:
Adaptive radiation occurs when an introduced species diversifies into multiple species to utilize different ecological niches, as seen in the Hawaiian honeycreepers and the Galápagos finches.
Step-by-step explanation:
When a few introduced plants establish adaptive radiation on an oceanic island, a population of a single species disperses across the island and adapts to distinct niches, leading to speciation events. This is seen in archipelagos like the Hawaiian Islands, where geographical isolation caused by the surrounding water encourages this process. A classic example of this phenomenon is the Hawaiian honeycreepers, which evolved from a single founder species into numerous species. Similarly, the finches observed by Darwin on the Galápagos Islands and the cichlids of Lake Victoria represent adaptive radiations, showcasing the rapid diversification into multiple species to fill available ecological niches.