“Dispersal ability, size change, loss of dispersal ability, endemism, relictualism, archipelago speciation, disharmony, and the rest – they are all characteristic of insular evolution and insular ecosystems, but nothing on that list is more characteristic than extinction. A high jeopardy of extinction comes with the territory. Islands are where species go to die.”
Flightless. Trusting. Unique. Doomed. About 300 years ago, the world lost a very special bird with the extinction of the giant pigeon that we know as the dodo. Hailing from the Indian Ocean island of Mauritius, the dodo is but one example of the fabulous, unique wildlife that evolved in isolation on the world’s islands. Among other familiar examples are the Komodo dragon, the Galapagos giant tortoise, the New Guinea birds of paradise, and the lemurs of Madagascar. Islands serve as spectacular laboratories of speciation, simplified ecosystems which have taught us much of what we know of evolution.
Lately, it seems that they’ve also taught us much of what we are learning about extinction.
The Song of the Dodo: Island Biogeography in an Age of Extinction is the opus of nature writer David Quammen (also the author of Monsterof God). It’s a masterpiece of evolutionary writing, managing to encompass everything from the drama of Darwin and Wallace’s race for primacy in unveiling the theory to the contemporary debate of how large and how many protected areas a species needs to survive. Tying this book together is one central theme – in evolution, islands are everything.
Islands, Quammen explains, are simplified ecosystem with fewer niches, fewer species, fewer connections, and fewer habitats than are seen on the mainland. In this respect, they act as sort of the “See Spot Run” of evolutionary theory – they are much less complicated than continental ecosystems, and therefore much easier to understand. It’s no coincidence that the two pioneers behind the Theory of Evolution through Natural Selection came to their conclusions after doing fieldwork on islands – Darwin in the Galapagos, Wallace in the Malay Archipelago.
Islands are defined by their isolation, and Quammen expends considerable time in exploring how they are populated, and by which species. Some are former chunks of the continent which get isolated through the rise and fall of the seas – hence why some Indonesian islands have tigers and others do not. Others are formed from the actions of volcanoes, and must be populated by pioneers, flying, swimming, or rafting their way across the ocean. If nothing else, the idea of islands populated by elephants swimming out to sea is pretty fascinating.
In time, islanders become defined by their isolation, and take on new, fantastic roles different from their mainland relatives. A monitor lizard becomes a ten-foot-long titan. An elephant becomes a dwarf the size of a pony. Lemurs cling to survival while their mainland relatives are competed and predated out of existence. One species of finch evolves into a dozen. And, yes, one awkward pigeon becomes flightless and fearless, leading to certain trouble when humans eventually show up.
And humans always eventually show up. Sometimes, the islanders get really unlucky, and the humans bring their “friends” – rats, mongooses, feral cats and dogs, or maybe an invasive,bird-devouring tree snake. Which is the other point that Quammen brings up – island species are, as a whole, far more vulnerable to extinction than their mainland counterparts.
The better chunk of Quammen’s book doesn’t even take place on islands… at least not in the conventional sense. He’s not the first to notice that many animals on the mainland are becoming isolated in islands of habitat, adrift in a sea of human-dominated landscape that is as inhospitable to the imprisoned animals as the ocean itself. A tiger in a national park in India is just as cut off from other tigers as a tiger on an Indonesian island. In these cases, studying actual island ecosystems provides a useful gauge for how these human-surrounded islands will behave… and what species will survive on them.
In his globe-trotting expose of islands, David Quammen takes the reader across the globe, from a feeding demonstration on Komodo (where a hapless goat is sacrificed to the maws of hungry dragons) to a tiny patch of rainforest in the middle of what used to be the unbroken Amazon. He also introduces the reader to a variety of scientists who brave extraordinary difficulties (in at least one case, involving being marooned and having to eat your study subjects) in the pursuit of knowledge.
The Song of the Dodo is a brick of a book, and feeling its heft in your hand (or seeing the page count on your eReader) can make it a little daunting. Don’t be fooled. From his elegant metaphor of the introduction to the satisfying conclusion, it’s an enjoyable read… except for the parts where Quammen tries to explain mathematical formulas. Even he doesn’t like those parts. More importantly, it provides an excellent footing in what island biogeography is, how it relates to the extinction crisis of today, and, above all, why you should care.