Tropic Islands Are Evolution Playgrounds
For Animal Adaptations And Animal Extinction

Tropic Islands: Earth’s Evolutionary Guards

By Rick Gregory

Tropic islands are old and young, large and small, remote and nearby.

For the planet's wild plant and animal species, these seemingly simple attributes play a major role in the progression of evolution and potential extinction.

Formed by the upheavals of tectonic shifting and the rise and fall of water levels over time since the Ice Ages, islands are where the evolutionary action is.

Scattered throughout the oceans in isolated pockets of protection, islands are biological laboratories and experiment stations.

Arising from the ocean floor as sea mounts or separated from the continental mainland, islands became refuges for stranded wildlife and places where wild creatures happen to make landfall. Limited habitats and few competitors for food resources formed idyllic conditions for some strange and unusual natural adaptations.

Some species became giants, others dwarfs. Some lost their ability to fly.

These are all traits that evolved when certain factors came together, allowing each to be expressed. But the main feature that jump-starts all of these odd and peculiar transformations is insularity. Away from large continental land masses, where animals freely come and go to find new niches, island living demands quicker changes for survival.

Tropic islands not only stand out on the map, they make evolutionary change stand out as well.

This distinctive quality is brought on due to their isolation and limited space. Borneo, Java and Sumatra were once connected to the Malay Peninsula, and the rest of Asia, during glacial periods when sea levels fell to expose the underlying Sunda Shelf. Mammals and other creatures, taking advantage of land bridges, dispersed across the wide plains of Sundaland. Later on as temperatures got warmer, sea levels rose to once again divide Sundaland into the Malay Peninsula and the assortment of islands of present day.

Evidence from fossil remains shows the effects of this geographical isolation over two million years ago. Early on, Sundaland was home to a number of elephant-like animals - mammoths, mastodons and stegodonts - as well as hippopotami, antelope and the sabre-toothed cat. Stegodonts were much larger than modern elephants and their tusks reached out twice as long. Later, dwarf species evolved among the elephants on the tropic islands of Suluwesi, Timor and Flores.

And imagine finding a 2.5 metre long giant pangolin crawling around the forest.

As the cooler periods thawed out, warmer climates and high water meant that island populations were unable to recolonize and became more vulnerable. Plants and animals either adapted to the new conditions or died out.

In Borneo, the Javan rhinoceros, the Malayan tapir and a wild dog species all succumbed to changes in the environment resulting from increased isolation. One survivor, the Sumatran rhinoceros, evolved from a long-legged species into a stockier animal with shorter limbs, signalling a possible adaptation to closed rainforests from more open savannah.

Most of what we know about the patterns of species distribution and the development of evolutionary theory derives from studying life on islands. Biogeography tries to separate out the facts of how plants and animals got to where they are or why they didn't make it to a particular place.

Island biogeography is what Charles Darwin was studying in the Galapagos Islands off Ecuador; the same with Alfred Russel Wallace in the tropic islands of the Malay Archipelago, both in the 1800s. By spending years collecting specimens and observing birds, tortoises and other wildlife in island habitats, these two researchers started a sequence of events that led each to the theory of natural selection, independently.

And the evidence from tropic islands put evolution in play.

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Read Part II: Charles Darwin and Alfred Russel Wallace

Read Part III: Islands of Animal Extinction: The Demise of The Dodo Bird

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

Go to Jungle Essays

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