“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.
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