Posted by: Dan | September 18, 2009

In the Age of Extinction

Biodiversity and endangered species are two topics on my mind today, along with a common response from Cypriots with regard to poaching and ambelopoulia here. That response being, “So what?”

With that, here is a quote (okay, more of an excerpt) from David Quammen’s book Song of the Dodo: Island Biogeography in an Age of Extinction, pages 605-607 (italics from original):

There’s a voice that says: So what?

It’s not my voice, it’s probably not yours, but it makes itself heard in the arenas of public opinion, querulous and smug and fortified by just a little knowledge, which as always is a dangerous thing. So what if a bunch of species go extinct? it says. Extinction is a natural process. Darwin himself said so, didn’t he? Extinction is the complement of evolution, making room for new species to evolve. There have always been extinctions. So why worry about these extinctions currently being caused by humanity? And there has always been a pilot light burning in your furnace. So why worry when your house is on fire?

Continued below the fold.

Biologists and paleontologists speak of a background level of extinctions throughout the history of life. That background level is the routine average rate at which species disappear. It’s generally offset by the rate of speciation, the rate at which new species evolve. These two together, extinction and speciation, constitute still another form of turnover — in this case, on the global scale. Rates of extinction in the remote past can’t be calculated precisely, because gaps in the fossil record prevent us from knowing what has been lost. But a cautious paleontologist named David Jablonski has made an informed guess, placing the background level at :perhaps a few species per million years for most kinds of organisms.” A few mammal species, a few bird species, a few fish species lost to extinction every million years — with that rate, evolution can keep up, adding a few species to each group by speciation. Such losses, counterbalanced by gains, yield no net loss of biological diversity. Extinction at that level, the background level, is an ordinary and sustainable process.

Against that background, a small number of big events have emerged to the foreground. These cataclysms, anything but ordinary, are the mass extinctions that scientists now recognize as major punctuation marks in the history of life. Some of them are famous: the Cretaceous extinction, the Permian extinctian. In such a mass extinction, compressed within a relatively brief span of years, the extinction rate far exceeds the rate of speciation, and the richness of the biosphere plummets. Niches fall vacant. Intricate networks of ecological relationships are thrown into disarray. Entire ecosystems are left raw and ragged. Millions of years pass, then, before speciation fills the gaps and brings the overall diversity back up to previous levels.

[…] It’s enough to note that mass extinctions of the first magnitude occurred at just five points in distant geological time, and that each was caused by some indeterminate set of natural factors among which humanity (not yet on the scene then) can’t be implicated. The Cretaceous extinction, 65 million years ago, claimed the last of the dinosaurs; the Permian extinction, 250 million years ago, eliminated more than half the extant families of invertebrate marine creatures. Other mass extinctions struck at the end of the Ordovician period (440 million years ago), in the late Devonian period (370 million years ago), and at the end of the Triassic period (215 million years ago, give or take a few million). Additionally, a sizable roster of large-bodied animals disappeared during the later millenia of the Pleistocene epoch, only tens of thousands of years ago, and in this case humanity may have been partly responsible; those Pleistocene extinctions occurred about the time that humans began hunting in armed and cooperative packs. Compared to the five big events, though, the Pleistocene spasm was minor, mostly confined to mammals.

And there have been still others, lesser episodes during which the extinction rate only modestly exceeded the background level. One way of defining a mass extinction as distinct from a lesser episode, according to Jablonski, is that it entails an extinction rate double the background level among many different plant and animal groups.

By this rigorous standard, we’re experiencing one now.

It started a few thousand years ago, when humans from Neolithic cultures along the fringes of the continents began venturing across the open sea in primitive boats. […] From the time of the Neolithic voyages until the present, twenty percent of the world’s bird species have gone extinct. During recent centuries, the rate of extinction has increased further and the range of jeopardy has widened — from birds to animals and plants of all kinds, and from islands to continents — as humanity’s impact has grown in direct correlation with the growth of human population, technological efficaciousness, and hubris. Nowadays it’s not just a question of dodos and elephant birds and moas. Nowadays we’re losing a little of everything.

Within a few decades, if present trends continue, we’ll be losing a lot of everything. As we extinguish a large portion of the planet’s biological diversity, we will lose also a large portion of our world’s beauty, complexity, intellectual interest, spiritual depth, and ecological health.


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