35 Adaptive Radiation

Adaptive Radiation

In some cases, a population of one species disperses throughout an area, and each finds a distinct niche or isolated habitat. Over time, the varied demands of their new lifestyles lead to multiple speciation events originating from a single species. We call this adaptive radiation because many adaptations evolve from a single point of origin; thus, causing the species to radiate into several new ones. Island archipelagos like the Hawaiian Islands provide an ideal context for adaptive radiation events because water surrounds each island which leads to geographical isolation for many organisms. The Hawaiian honeycreeper illustrates one example of adaptive radiation. From a single species, the founder species, numerous species have evolved, including the six in Figure 1.

The illustration shows a wheel with the founder species at the hub. The spokes of the wheel are six modern honeycreeper bird species that evolved from the founder bird species. Five of these birds eat insects and or nectar and have long, thick beaks; these are the Apapane, Liwi, Amakihi, Akiapola'au and Maui Parrotbill. The Nihoa Finch has a short, fat beak and eats insects, seeds, and bird eggs.
Figure 1: The honeycreeper birds illustrate adaptive radiation. From one original species of bird, multiple others evolved, each with its own distinctive characteristics.

Notice the differences in the species’ beaks in Figure 1. Evolution in response to natural selection based on specific food sources in each new habitat led to evolution of a different beak suited to the specific food source. The seed-eating bird has a thicker, stronger beak which is suited to break hard nuts. The nectar-eating birds have long beaks to dip into flowers to reach the nectar. The insect-eating birds have beaks like swords, appropriate for stabbing and impaling insects. Darwin’s finches are another example of adaptive radiation in an archipelago.

LINK TO LEARNING


Watch this video to learn how island birds evolved in evolutionary increments from 5 million years ago to today.

Glossary

adaptive radiation
speciation when one species radiates to form several other species

Access for free at https://openstax.org/books/biology-2e/pages/1-introduction

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Introductory Biology: Evolutionary and Ecological Perspectives by Various Authors - See Each Chapter Attribution is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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