The kites fly again

The iconic movie Jurassic Park has provided us with quite a number of quotable lines:

"I hate it when I'm always right."

"Clever girl."

"That is one big pile of shit."

"See?  Nobody cares."

"Hold onto your butts."

But as someone who has studied (and taught) evolution for decades, none of them has stuck in my mind like Ian Malcolm's pronouncement, "Life... uh... finds a way."

This short sentence sums up something really profound; however the Earth's ecosystems are damaged, they always bounce back.  Even after the catastrophic Permian-Triassic Extinction -- which by some estimates wiped out 90% of the existing taxa on Earth -- there was a recovery and rediversification.

Note that I'm not saying that means it was a good thing.  The end Permian extinction event was, it is believed, caused by an unimaginably huge series of volcanic eruptions, followed by a major spike in the carbon dioxide content of the atmosphere -- leading to a jump in the global temperature and catastrophic oceanic anoxia.

So yeah.  "Life survived" doesn't mean it'd have been a fun event to live through.  But it should give us hope that the damage humans can do to the Earth as a whole is, in the grand scheme of things, short-lived.

As an encouraging example of this, take a recent study out of the University of Florida on snail kites.  These birds, related to hawks and falcons, are serious food specialists; they eat only one species of snail, found in salt marshes like the Everglades (and also parts of Central America; I first saw snail kites in Belize).  When things are stable, being a specialist is a good thing -- you pretty much corner the market on a particular resource, like the South American hummingbird species whose bills are shaped to fit one and only one species of flower.  The snail kite's food finickiness is this same sort of thing, and as long as the Everglades was undamaged and had an abundant supplies of snails, all was well.

[Image licensed under the Creative Commons Bernard DUPONT from FRANCE, Snail Kite (Rosthramus sociabilis) Poconé, Mato Grosso, CC BY-SA 2.0]

But when the environment is rapidly changing, either through human effects or because of natural events, being a specialist is seriously precarious.  When a new species of snail -- the island apple snail -- was introduced to the Everglades, its larger size and voracious appetite outcompeted the native snails, and the snail kites were in trouble because their bills weren't large and heavy enough to tackle the bigger prey.

Snail kites were already on the Endangered Species List, given that the Everglades has been massively damaged by human activity.  This, it seemed, might be the death blow to the Florida population of this striking bird.

But... life, uh, finds a way.

The snail kite, in a near-perfect reenactment of the bill diversification in Darwin's finches in the Galapagos, had a variety of bill sizes.  Genetic diversity, despite their extreme specialization.  Before the introduction of the island apple snail, bill size probably didn't make much difference, positive or negative, to the individual birds.  But now, large bills were a serious advantage.  The birds with the biggest bills could tackle the larger snail species -- meaning they had a copious food source that their smaller-billed cousins couldn't utilize.

And in the thirteen years since the introduction of the island apple snail, the average bill size has gone up dramatically -- and the overall population is rebounding.

"Beak size had been increasing every year since the invasion of the snail from about 2007,” said Robert Fletcher, who co-authored the study.  "At first, we thought the birds were learning how to handle snails better or perhaps learning to forage on the smaller, younger individual snails...  We found that beak size had a large amount of genetic variance and that more variance happened post-invasion of the island apple snail.  This indicates that genetic variations may spur rapid evolution under environmental change."

As I said earlier, this is not meant to give the anti-environmental types another reason to say, "Meh, we don't have to change what we're doing, things'll be okay regardless."  Most species aren't as fortunate as the snail kites, already having the genetic diversity to cope with a sudden change.  Much more likely, if we keep doing what we're doing, the specialist species in the world will simply be wiped out.

Whether we'll be able to survive in such a changed world remains to be seen.

But one thing is nearly certain; even if we catastrophically damage the global ecosystem, it will rebound eventually.  Which is hopeful, as far as it goes.  Even after Homo sapiens is another fossilized footnote in the Earth's geological history, life will persist -- once more generating, in Darwin's immortal words, "endless forms most beautiful and most wonderful."

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 Many of us were riveted to the screen last week watching the successful landing of the Mars Rover Perseverance, and it brought to mind the potential for sending a human team to investigate the Red Planet.  The obstacles to overcome are huge; the four-odd-year voyage there and back, requiring a means for producing food, and purifying air and water, that has to be damn near failsafe.

Consider what befell the unfortunate astronaut Mark Watney in the book and movie The Martian, and you'll get an idea of what the crew could face.

Physicist and writer Kate Greene was among a group of people who agreed to participate in a simulation of the experience, not of getting to Mars but of being there.  In a geodesic dome on the slopes of Mauna Loa in Hawaii, Greene and her crewmates stayed for four months in isolation -- dealing with all the problems Martian visitors would run into, not only the aforementioned problems with food, water, and air, but the isolation.  (Let's just say that over that time she got to know the other people in the simulation really well.)

In Once Upon a Time I Lived on Mars: Space, Exploration, and Life on Earth, Greene recounts her experience in the simulation, and tells us what the first manned mission to Mars might really be like.  It makes for wonderful reading -- especially for people like me, who are just fine staying here in comfort on Earth, but are really curious about the experience of living on another world.

If you're an astronomy buff, or just like a great book about someone's real and extraordinary experiences, pick up a copy of Once Upon a Time I Lived on Mars.  You won't regret it.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

Kite flying

A few years ago, I wrote a post here at Skeptophilia called "Grass, gulls, mosquitoes, and mice," in which I laid out the argument that while evolution is usually slow, sometimes it's so fast we can see it happening before our very eyes.  And when that happens, the anti-evolutionists amongst us have some explaining to do.

It's always nice to have another arrow in your quiver, and that came in a recent paper in Nature called, "Rapid Morphological Change of a Top Predator With the Invasion of a Novel Prey," by Christopher E. Cattau, Robert J. Fletcher Jr, Rebecca T. Kimball, Christine W. Miller, and Wiley M. Kitchens, all biologists at the University of Florida, who have been studying Snail Kites, a rare bird of prey found in the Everglades (and, as you'll see, in a few other places).

The Snail Kite, as you might expect from the name, is a specialist predator that feeds only on apple snails, a large species of freshwater gastropod found in the Everglades.  They have hooked beaks for removing the meat from the snail, and taloned feet for holding onto the shell -- well adapted for their niche.

The problem started with the accidental introduction into Florida of the island apple snail (Pomacea maculata), a larger, heavier species native to Argentina.  The native species, the Florida apple snail (Pomacea paludosa), was quickly outcompeted in areas where they both occurred, which concerned not only fans of the Snail Kite but rice farmers, as the island apple snail is a voracious pest on rice crops.

[Image licensed under the Creative Commons, photograph by Andy Morffew]

When an exotic species replaces a native species upon which other animals depend for food, the usual result is a drastic blow to the pre-existing food chain.  Here, though, we have a different result -- an eye-opening response by the Snail Kites that recalls evolutionary biologist Alan Grant's comment in Jurassic Park that "nature finds a way."

As is, the Snail Kites in Florida were not equipped to prey upon the island apple snails -- their feet were too small to hold onto the shells, not surprising as the snails are five times larger than the native Florida apple snails.  But the expected drop in the bird's numbers didn't happen.  Instead, in only a couple of generations, selection was so powerful on the population that the average talon size and bill size increased measurably, and the alterations were reflected by changes in their DNA.

"Nobody would believe me," said Robert Fletcher, co-author of the study, when the findings were announced. "They said, 'No, that cannot be. It's too quick.'"  But even the naysayers were convinced when the introduced snail species showed up in huge numbers in one part of the Snail Kite's range, and instead of leaving the premises, nearly all of the nearby kites converged on the spot.

I guess birds like an all-you-can-eat buffet as much as the rest of us do.

The authors write:

[T]rends in predicted breeding values emphasize that recent morphological changes have been driven primarily by phenotypic plasticity rather than micro-evolutionary change.  Our findings suggest that evolutionary change may be imminent and underscore that even long-lived vertebrates can respond quickly to invasive species.  Furthermore, these results highlight that phenotypic plasticity may provide a crucial role for predators experiencing rapid environmental change.

It's good news for the kites, but it bears mention that a lot of times, the introduction of an exotic species can spell disaster for native ones.  The kites were lucky in that there was already a range of bill sizes because of spontaneous mutations, and the new prey acted as a selecting agent, favoring the largest-billed and largest-footed individuals.

The most interesting part is that once you set this in motion, it ultimately will split the population from related populations elsewhere.  I first saw Snail Kites in Belize, where there are no island apple snails, so the pressure to cope with bigger prey doesn't exist.  Given time -- and, apparently, less time than anyone thought -- the population in Belize and the one in Florida will diverge genetically to the point that they will be, by anyone's definition, different species.

So there you have it: another example of evolution in action.  Cool enough for anyone to appreciate, but for evolutionary biologists, this is nothing short of spectacular.  We can add this to the list of times we've actually observed species evolving quickly enough to see it happen -- which is one more nail in the coffin of strict creationism, not that we particularly needed another one.

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Ever wonder why we evolved to have muscles that can only pull, not push?  How about why the proportions of an animals' legs change as you look at progressively larger and larger species -- why, in other words, insects can get by with skinny little legs, while elephants need the equivalent of Grecian marble columns?  Why there are dozens of different takes on locomotion in the animal world, but no animal has ever evolved wheels?

If so, you need to read Steven Vogel's brilliant book Cats' Paws and Catapults.  Vogel is a bioengineer -- he looks at the mechanical engineering of animals, analyzing how things move, support their weight, and resist such catastrophes as cracking, buckling, crumbling, or breaking.  It's a delightful read, only skirting some of the more technical details (almost no math needed to understand his main points), and will give you a new perspective on the various solutions that natural selection has happened upon in the 4-billion-odd years life's been around on planet Earth.

[If you purchase the book from Amazon using the image/link below, part of the proceeds goes to supporting Skeptophilia!]