Adventures in the Pacific
Whatever their size or origins, the species and the ecosystems of islands are exquisitely sensitive to invasion. Whether arriving by themselves or by human agency, invaders can be fatal to the original inhabitants, and virtually no island survived into the last century unscathed. After humans the most common invaders are introduced rats—though cats, snakes and even snails have time and again devastated entire islands of unique species.
Why should the long-isolated islanders be so vulnerable? Island species often have only a limited range of predators, competitors and diseases. Under such circumstances, any species that invests too much energy in being able to flee swiftly or in producing toxins that deter predators will, prior to the arrival of new invaders, be outcompeted by those that put less effort into these faculties and more into reproduction. This is why so many island birds are flightless and why the nuts and leaves of so many island trees are edible, even without cooking—trees that invest in toxins where there are no predators, rather than making more nuts and fruit, are disadvantaged in the evolutionary race for survival. But island species also lose their fear. Fearful creatures use a great deal of energy in fleeing danger, both imagined and real. Where the danger is almost entirely imagined, evolution selects for individuals that conserve their energy for reproduction. Island birds have been known to sit on their nests even while being eaten alive by rats. Many will not flee from cat or human, even when attacked.
As colonial history has shown, the native cultures of islands are also vulnerable to change from outside. The power structures of Hawaii were transformed by a dozen or so iron blades fashioned by a ship's cooper during Captain Cook's voyage of discovery. So armed, the few fortunate chiefs who received them went on to forge empires. What is remarkable, however, is how much traditional island culture still survives in spite of the constant waves of challenge arriving from the larger world. Change may be integral to island life—as old as the first island and as pervasive as the sea that surrounds them all—but such examples convince me that, given half a chance, much that is unique to the islands can persist.
The continent of Australia has cast a long shadow over the extensive archipelago we explored—a shadow composed of living things that, over the aeons, have drifted, flown or made their way some other way to the islands. Among them are curious marsupials, unique birds of paradise and countless other life-forms which have their points of origin millions of years ago on the wide brown land. But what a sea change was wrought on their descendants as they settled into island living. Such species are utterly irresistible to biologists because their myriad modifications reveal the secret workings of evolution. When the animals' ancestors left, Australia's rainforests were extensive, and a vestige of ancestral forms long vanished from the larger landmasses can be found on some islands. Examining such plants and animals can reveal living clues to a now vanished and very different Australia.
We twentieth-century biologists travelled through the vast island realm that was our field of research by whatever means were at hand—sometimes by air, at others by ocean liner, interisland ferry or dugout canoe. Then we would set about collecting, documenting and exploring a world of nature that in some cases had never before been entered by a biologist. And the excitement of setting up a mist-net and laying a trap-line on an island which had not yielded a single record of a mammal was just about the most exciting thing you could do.