Adaptive radiation
Many species evolving from one ancestor in one area, each suited to a different habitat, is adaptive radiation. Examples: Darwin's finches and Australian marsupials.
Darwin's finches
On the Galapagos Islands, Darwin saw many varieties of small black birds, later called Darwin's finches. He thought they all evolved on the islands themselves. The original finches were seed-eaters. From them arose many forms with altered beaks, so some became insect-eaters and others vegetarian (plant-eaters). This process of many species evolving in one area, starting from one point and spreading into different habitats, is adaptive radiation.
Australian marsupials
- Marsupials are pouched mammals; the young finish growing in the mother's pouch.
- In Australia, a single ancestral marsupial stock gave rise to many very different marsupials.
- Examples: kangaroo, koala, wombat, bandicoot, Tasmanian wolf, marsupial mole, banded anteater (numbat), sugar glider, marsupial rat, spotted cuscus and Tasmanian tiger cat.
- Each became suited to a different way of life: grazing, burrowing, gliding, hunting, eating ants.
Placental mammals and their marsupial look-alikes
| Placental mammal | Australian marsupial | Shared way of life |
|---|---|---|
| Wolf | Tasmanian wolf | Hunting other animals |
| Mole | Marsupial mole | Burrowing |
| Anteater | Numbat (banded anteater) | Eating ants |
| Mouse | Marsupial mouse | Small, quick animal of the ground |
| Flying squirrel | Flying phalanger | Gliding between trees |
| Lemur | Spotted cuscus | Living in trees |
| Bobcat | Tasmanian tiger cat | Hunting smaller animals |
Adaptive radiation vs convergent evolution
When more than one adaptive radiation occurs in an isolated area, the look-alikes they produce show convergent evolution.
India's Western Ghats show the same pattern on a small scale. From a few ancestral frogs, many species have evolved to live in streams, on leaves, on the forest floor and in tree holes. Protecting varied habitats protects this living record of evolution.
2 marks: “What is adaptive radiation? Give one example.” Evolution of different species in a given geographical area from one ancestor, radiating into different habitats. Example: Darwin's finches of the Galapagos, or Australian marsupials.
3 marks: “Explain how Australian marsupials and placental mammals show both adaptive radiation and convergent evolution.” Each group radiated from its own ancestor into many forms. Placental forms came to resemble marsupials with the same way of life (wolf and Tasmanian wolf; flying squirrel and flying phalanger): convergent evolution.
Radiation = Radiating from one root; Convergence = Coming together in look.