Evolution Speeds Up Adaptations On Islands
Where Animal Extinction Provides Lessons

Islands of Evolution: Animal Adaptations and Animal Extinction

By Rick Gregory

The intelligence gathering for natural selection occurred mainly on tropic island habitats.

Starting with Charles Darwin and Alfred Russel Wallace and followed up by a multitude of biologists, ecologists, zoologists and other curious researchers, life forms found on islands were visibly different from those found on continental mainlands.

• For example, what could explain the larger size of the komodo dragon of Indonesia?
• How did the famous, but now extinct, dodo bird of Mauritius end up flightless?
• What factors made it possible for giant tortoises and sea-diving iguanas to evolve on the Galapagos Islands?
• Why are some island species unafraid of humans or other potential enemies?

Both evolutionary and ecological forces are in play in the process of change. Most changes occur at the species level, where evolution leads to differences in size, mobility, colour, and location. In contrast, ecological changes affect community dynamics with both positive and negative results.

For various biological reasons, island mammals tend towards dwarfism, while island reptiles lean towards gigantism. Other species, such as birds and beetles, have arrived by flight to island habitats, only to evolve wings of little use down the evolutionary road. Many island species are endemic, living and dying in restricted localities; while others are relics, cut off from animal populations gone extinct on the mainland.

Animal evolution is slow; animal extinction is rapid. It has taken thousands of years for many animals to evolve and survive the onslaught of natural disasters, species invaders and climatic and habitat changes. Scientists have only just begun to understand the complex dynamics and interrelationships of species distribution and animal adaptations.

It's a painstakingly slow process that must be proven with each new discovery or theory presented. For many species time has already run out, but for others the lessons learned from island studies may yet prove to be beneficial.

On the enchanting Indonesian island of Bali, a smaller sub-specie of tiger once prowled its finite forests. Not much was really known about the Bali tiger because it became extinct just 30 years after it was first described in the early 1900s.

And there wasn't much that could be done for the sub-species anyway. Coupled with escalating habitat destruction and hunting, the Bali tiger was doomed to die out without any room to move or an influx of new members.

The Javan tiger suffered a similar fate. Although it lasted fifty years longer, the demand for skins and conflicts with villagers bolstered hunters to kill them by the hundreds. Sumatra is now the only island left in Indonesia where tigers still remain.

So why do researchers fuss over animal extinction of small populations on small islands? Are there not tiger species in other parts of the world, such as on the larger continent of Asia? Again the study of island biogeography leads us to some answers and, of course, more questions. In the last few hundred years, island birds were studied quite extensively. Or at least more data is available for avian fauna than for mammals and reptiles.

As pointed out by David Quammen in The Song of the Dodo: Scientists have tallied up the losses since the 1600s and found that 171 species and sub-species of bird are no longer counted among the planet's biodiversity. Out of the total number of species extinctions, over ninety percent (155 species) lived on islands. That's an astonishing number!

To make matters worse, only twenty percent of the world's bird species are restricted to islands. This means that most extinction occurred in habitats housing a limited number of species. And to complete this dire scenario, it was found that seventy-five percent of island extinction events occurred on smaller, rather than larger islands.

Do these bird extinction rates on small islands signal similar problems for animal extinction of reptiles, mammals and other biological treasures?

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Read Part I: Tropic Islands: Earth's Evolutionary Guards

Read Part II: Charles Darwin and Alfred Russel Wallace

Read Part IV: Terrestrial Islands: Breaking Up The Rainforest Biome

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