Islands, Evolution, and a book report

Academics love to keep books, such that they accumulate over the years until, one day, you move offices, change universities, or retire and give them all away.  I happened upon one of these give-away treasure troves recently and grabbed several older books.  I began my journey with a historical perspective on island biogeography, and I enjoyed it so much I thought I’d write about it.

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The book is “The Song of the Dodo: Island Biogeography in an Age of Extinctions”, written in 1996 by David Quammen.  David is a science writer, but has also written some fiction, and at the time this book was published lived in Montana, from where I so recently emigrated.  It’s written in a meandering way, weaving together textbook information, historical accounts of ecologists from the last few centuries, and his own experiences traveling the world to visit the unique locations that inspire(d) scientists to brilliance.  While it certainly helps to have a background in biology or ecology in order to fully appreciate the book, it’s seems interesting enough to grab a more general audience.

Be prepared for a feast of delicious jargon, though:

“The Origin of Species is a book of encyclopedic richness and inexhaustible tediousness, a great potpourri of argument and fact in which a reader can find almost anything a reader might want: Lamarckism, animal husbandry, geology, ethology, experimental botany, the kitchen sink, island biogeography.” pg. 200

So what is island biogeography? It’s the study of how species are distributed across an environment; specifically on islands.  Sounds simple enough.  Let’s go back to the Age of Exploration (late 1400s to the late 1700s) when new technology and a growing appreciation for the size of the planet gave rise to a burst of exploration.  Suddenly- and this historical perspective is very Euro-centric- new lands, geology, peoples, plants, and animals were being discovered, and tales of the exotic made it back to Europe.  Sometimes, preserved animal specimens would make it back to Europe, which was extremely tricky as they had to be prepared in the field, usually by skinning or pickling.  Often, the heads, feet, tails, or wings would be removed during the process, accidentally or intentionally.  This only fueled the mystery more: many species of Birds of Paradise had their feed removed during processing, leading British ecologists, many of whom were working off secondary information and had never traveled to these locales, to believe that these birds had no feet at all and lived entirely among the clouds until their death when they fell to the ground.

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Birds of Paradise, Natural History Museum of Utah

The lure of discovering new, fabulous species was irresistible, and naturalists began expeditions all over the globe to make observations and collect specimens.  Largely, collectors interested in one particular animal or insect would select a small number of specimens for each species they collected, thus they accidentally missed the natural variations in size or color that one sees in wild animals.  After all, one doesn’t always notice little differences when only looking at a few examples.  Or, they would fail to record the particular location of their find, often only labeling it only by the continent on which is was collected.  But some naturalists were more curious.  They collected more specimens, more data, and began to notice patterns.

The most important pattern was that not all animals were found everywhere.  Certainly, it was noted that certain animals were specific to a habitat- sharks to the ocean, camels to the desert, etc.  But it wasn’t until people discovered animals found exclusively on islands that it really sunk in.  And this is extremely important, because it begged the question: why?  Why are some animals in one place and not another?  How did they get there?  The prevailing theories until that point were largely based on stories from the Christian bible, but with the discovery of so many new species, a literal ark was increasingly going to be improbably overcrowded.

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Geography and Evolution

Long story short, many ecologists actually began as geologists- Charles Darwin included, and in studying island formation it became understood that some island animals had crossed on land bridges, while others flew, swam, or drifted onto islands.  The species and mode of arrival very much determined whether you could then get back off the island, or whether you were stuck.  Ok, so now we know that animals can travel and change their own habitat location (which is different from migration), which went against the prevailing theory that animals were located where they had been put during a creation event.

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Finches

The next important pattern was that multiple, closely-related species could exist in a place at the same time.  In the years following his voyage while studying the specimens he collected, Charles Darwin noticed this of the mockingbirds, tortoises, and eventually the finches on the Galapagos, which was just a brief stop on his 5 year geology cruise aboard the Beagle (1831-1836).  Again, this was important, because what was the likelihood that all these similar bird species came to the same island chain at the same time?  It was more likely that a few birds of a single species had come over, and these birds had changed over thousands of generations into several new species.  The accepted notion was that animals didn’t change- they remained as they had been created.  The idea that a species could change or evolve over time was, at best, silly and at worst, blasphemous.

Nevertheless, a number of ecologists had made reference to the possibility of change during the Age of Exploration, but lacked solid data and a concrete theory of how. The mockingbirds represented true archipelago speciation; one species came to the Galapagos islands and populations became isolated on separate islands until through genetic drift they became different species, but there were only four mockingbird types and that was little enough to go on.  On the other hand, Darwin had 31 individuals representing what he thought was 14 unrelated bird species, but it wasn’t until after his voyage, when an ornithologist properly classified the birds as all being closely-related finches, that Darwin paid any attention to them at all.  In fact, Darwin nearly missed the idea of evolution because he failed to label which island his finches came from and very little about their ecology or behavior- he had to gather missing data from other accounts for years before he could see a real pattern. To be fair, the finches are a much more complicated pattern because they display adaptive radiation; one species arrived on the islands, but populations were only transiently isolated and when they crossed paths again they were still similar enough to compete, so different species evolved to fill different ecological roles (niches) in order to avoid starvation due to competition.

Darwin’s first account of his Beagle voyage made just a brief mention of this observation on closely-related species, but it changed the life of Alfred Wallace.  Wallace came from a poor background, and eventually paid for his love of naturalism and data collection by selling the specimens he collected.  Many British naturalists at the time were wealthy, and selling one’s collection seemed base- thus Wallace, with no title or reputation, was dismissed for most of his early career.  Years after Darwin went to the Galapagos, Wallace went to South America and Indonesia and came to the same conclusion about multiple closely related species: that one species had become many.  Wallace made the jump to speciation much faster, and sent Darwin a manuscript that was frighteningly similar to the yet-unpublished Origin of Species, which Darwin had worked on for 20 years to gain enough proof to avoid being laughed at.  Social politics aside, which are discussed in the book, a joint manuscript was presented, On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection, and a year later Darwin published On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life, which, incidentally doesn’t even mention Galapagos finches.

The idea of macroorganismal evolution was difficult to come by, largely because it’s a much longer process than a human can witness, and because a possible mechanism for change was completely unknown (genetics was a long way away).  By studying islands, ecologists could study evolution in miniature worlds where the pressure to stay alive was great- indeed, many species were marooned on the islands they colonized.  Studying this, and the livestock breeding industry, gave rise to the idea in Darwin’s mind of Natural Selection– that external forces could change a species over time by forcing the species to change.

Because animals are isolated on islands, they change to fit that particular ecosystem in a very visible way.  Wallace noticed this happening in his travels in South America where large rivers converged: animals that could not cross the river became isolated and there would be similar but distinct species on each side of the river.  Again, the whimsical biogeography of a deity became less probable than natural forces (food, geography, predation, competition) driving the distribution of animals and plants.  Still, it took decades to iron out the particulars of evolution, and even today people refuse to acknowledge it.

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Natural Selection, Understanding Evolution

But this book isn’t solely a historical account- all of that is setting the stage for a larger picture: extinction.  For even as island pressures select for the creation of species distinct from those found on mainlands, it also selects them for extinction.  Islands are partially or completely isolated, and this means any breeding population is small to begin with, and eventually can become inbred.  Island populations often collapse: the gene pool becomes too stagnant, a natural disaster hits, food becomes scarce, a predator appears.  Because there are only so many individuals, and because they are adapted to a very specific location, island species can’t deal with change.  Unfortunately, humans bring nothing but change.  As we develop natural land for our own use we fragment habitat, and for animals that can’t cross a city to get to the other populations, their gene pool and food options are limited.  They become reliant on very specific living conditions in their small habitat fragments, and they are more susceptible to disease, inbreeding, predators, and climate change.  The smaller the habitat, the fewer the individuals, and the ore they struggle to survive.  As humans colonize all parts of the globe we are leaving man-made islands in our wake, with marooned populations of plants and animals that find it increasingly difficult to sustain themselves- we are the cause of the mass extinction of animals and plants around the globe that only trickles into our mainstream news.

“We still argue about when it [the dodo] actually became extinct, but it probably disappeared around the 1660s.  It’s become the sort of legendary bird of extinction.  And a very important bird.  There were extinctions before and there’s been lots of extinctions since, but it was an important extinction because that was the first time, the first time in the whole of man’s history, that he actually realized he had caused the disappearance of a species.”

-interviewing Carl Jones about the extinction of the dodo, pg. 277

The level of detail provided in The Song of the Dodo is fascinating, especially because historical accounts so often lose sight of a who a person was and the journey they had to take.  Darwin wasn’t always correct, other scientists had the right theories but the wrong data to prove them, and the elitism of early science often led to the adoption of incorrect theories from otherwise brilliant men.  The book gives an honest perspective- that all scientists are trying their best to make sense of the information they have, and that it can take an extremely long time to put the entire puzzle together.  And it gives cause for hope.  While we may not be able to bring back populations of species we have pushed to the brink, life is pluripotent.  If we give the natural world some space- it’ll grow back.

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