Do not cross

Back in 1859, renowned British naturalist Alfred Russell Wallace wrote a paper about a peculiar phenomenon, which has since been called Wallace's Line in his honor.  He had noted that west of a wavering line that runs basically from northeast to southwest across Indonesia, the flora and fauna is much more similar to what you find in India and tropical southeast Asia; east of that line, it resembles what you find in Australia and Papua-New Guinea.

Map from Wallace's original paper [Image is in the Public Domain]

The change is striking enough that it didn't take a naturalist of Wallace's caliber to notice it.  Italian explorer Antonia Pigafetta mentioned it in his journals way back in 1521, and various others considered it a curiosity worth noting.  None, though, did the thorough job of studying it that Wallace did, so naming it after him is justified.

However -- even Wallace had no idea why, or how, it had happened.

Ordinarily, faunal and floral assemblages change gradually, unless there's a major geographical barrier.  I saw an example of the latter first-hand when I was in Ecuador -- there's a completely different set of birds as you cross from the west slope to the east slope of the Andes Mountains.  (Some did make the leap, but by and large, you run into a whole different group of species from one side to the other.)

Here, though, there's no obvious barrier.  In fact, if you'll look closely at the map, you'll see that Wallace's Line goes right between the islands of Bali (on the west) and Lombok (on the east) -- a distance of only 35 kilometers, easily narrow enough for birds to cross, not to mention other species swimming or rafting their way from one island to the other.  Even so, the species on Bali are distinctly Asian, and the ones on Lombok distinctly Australian.

On one side, kangaroos and koalas, cockatoos and birds of paradise and cassowaries; on the other, bears and tigers, trogons and drongos and minivets and babblers.

How did this happen -- and more perplexingly, what's kept the line intact?

The explanation for the first part of this question had to wait until the discovery of plate tectonics in the 1950s.  The Australian region and Asia have very different species because they are on different tectonic plates that used to be a great deal farther away from each other; in fact, until 85 million years ago, Australia was connected to Antarctica (something we know not only from our understanding of plate movement, but because prior to that Australia and Antarctica have similar fossils, which began to diverge at that point as Australia moved north and Antarctica moved south).  Australia has been gradually approaching Asia ever since, with its unique assemblage of species riding in like some latter-day Noah's Ark.

What, though, is keeping them from mixing?  The reason the topic comes up today is because of a paper last week in Science that has proposed a neat explanation; the problem is the climate.

Researchers at ETH-Zürich led by evolutionary biologist Loïc Pellissier noted that there were exceptions to the boundary of Wallace's line, but the species that crossed it almost always went one way -- from the Asian region into the Australian region.  Some species of Australian snakes, for example, have their nearest relatives in Asia, as do the wonderful Australian flying foxes.  But there are virtually no examples of species that went the other way.

What was preventing organisms from island-hopping their way from Australia to Asia was Asia's much wetter climate -- if you go from west to east across Indonesia and into Australia, the average rainfall by and large goes steadily downward.  The contention is that it's easier for organisms from a rainy climate to adapt to gradually drying out than it is for extremely dry-adapted organisms to deal with the already high biodiversity (and thus much higher competition with species already well suited to the conditions) found in more rainy regions.

You have to wonder what will happen when Australia and Asia finally collide -- something that is, in a sense, already happening, but will result in a complete fusion of the two continents in two hundred million years or so.  This will result in a situation a little like the collision of India with Asia eighty million years ago, which raised the Himalaya Mountains.  (In fact, that collision is ongoing; as India pushes north, like a giant plow, the Himalayas are continuing to rise.  Which is why you find marine fossils at the top of Mount Everest -- the Himalayas aren't volcanic, they're marine and continental debris scooped together and piled up by the motion of India.)

The collision of Australia and Asia will, of course, eradicate Wallace's Line (although the mountain range it will create could still provide a barrier for species mixing, just as the Andes do in Ecuador and Peru).  Of course, two hundred million years is a very long time -- about three times as long as it's been since the extinction of the non-avian dinosaurs -- so who knows what species will have evolved in the interim?

Or if we'll have any distant descendants of our own around to see it?

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A study in tropical colors

As my regular readers know, I just got back a couple of days ago from a two-and-a-half week trip to Malaysia.  I thought it might be interesting to step aside for a day from my usual agenda of lobbing verbal bombs at the woo-woos, and give a few of my impressions of this country.

I was drawn to Malaysia by the birds.  I am a fanatical birdwatcher, an avocation that I am more and more beginning to think of as being some kind of benign mental disorder.  The trip was an organized excursion put together by Birdquest International, a UK-based company that specializes in taking people to where the birds are.  So everyone on the trip shared my obsession -- all seven participants, and the two guides.  We shuffled along the trails in a tight, silent little pack, binoculars in hand, scanning trees and underbrush, listening for unusual calls or songs -- and then launching into action like a SWAT team when one was seen:  "Bulbul!  Olive-winged!  Large tree with round leaves, in foreground, nine o'clock, moving left!"  And everyone would swivel around to find the bird, and one by one you'd hear, "Got it, thanks!" and every once in a while a "Dammit!  It flew!"

But the birds were spectacular.  The grounds of the lodge where we stayed in Taman Negara National Park were frequently graced by four or five Crested Firebacks, a pheasant species that looks like it's ready for a fancy costume ball.  Not all of them were that easy; it took us several hours of work to locate the elusive Garnet Pitta, a bird that has been called the Jewel of the Rain Forest (photo courtesy of the Wikimedia Commons):

We never, ever were without our binoculars, except when we were sleeping.  We wore them at meals, during rides in the van from one locale to another, and when we were hauling our luggage around.  And all it took was the cry of "Bird!" to stop us from all other pursuits and hoist the lenses into the air to see what might have flown in.

Of course, it's not that that was the only attraction to Malaysia.  It's a stunningly beautiful country, with huge stands of pristine rain forest, enormous trees draped with lianas and ferns.  A botanist would go mad here from the diversity of plant life.  I pride myself on my knowledge of plants, and I only recognized perhaps 10% of what I was seeing.  Take this strangely-shaped leaf for example:

No idea what it is, other than "cool."  Because of the thin soils, most of the trees have these sculpted buttress-roots, that never failed to remind me of Old Man Willow from The Lord of the Rings:

Besides the biology of the place, there's the culture.  The food was always interesting, and often delicious.  We had a hundred different takes on curry, most with coconut, a food I heartily approve of.  I finally got to try durian, the famous spiky (and smelly) fruit of Southeast Asia.  Durian has such a pungent smell that it is illegal to open one on public transport or in a hotel room, and I found first-hand that the smell clings to your skin and clothing for hours.  What does it smell like?  Let me quote food writer Richard Sterling: "Its odor is best described as pig shit, turpentine, and onions, garnished with a gym sock."  Anthony Bourdain, even though he likes the stuff, says that after eating it "your breath smells like you've been French-kissing your dead grandmother."  So, of course, I had to try it.  And... I thought it was delicious.  The flavor is kind of indescribable -- musky, sweet, creamy, a little oily.  But definitely wonderful, and like nothing else I've ever tasted.

I also ran face-first into sambal ulek, which I have renamed "Malaysian Death Sauce" because I had no idea how freakin' hot it was until I had slathered it all over my breakfast.  Now, I'm from southern Louisiana, and have a very high (probably genetic) tolerance for pepper, and this was hotter than anything I've ever eaten.  It was only my hatred of losing face amongst comparative strangers that kept me from dumping my plate and taking a second serving with three drops (rather than three heaping spoonfuls) of the stuff.

And speaking of hot: Malaysia is also the other kind of hot.  The temperature varies from blazing hot, all the way up through sauna and right into the realm of pressure cooker.  I was constantly wringing wet with sweat, and I usually have a high tolerance for hot weather.  In the highlands (we spent four days at Fraser's Hill in the Cameron Highlands of central Malaysia) it was a bit cooler, but that's like saying that "compared to a blast furnace, a bread oven is comfortable."  It was still near 100% humidity, and I think the temperature only dropped below 80 F for a brief time at night.

The heat and humidity also encourage a variety of animal life, and not all of it is of the oh-look-at-the-cute-little-monkey type.  Malaysia has leeches.  Terrestrial leeches.  These live in the leaf-litter of the forest floor, attach themselves to your shoes, and then crawl up your pant leg in search of dinner.  Most of our party got bitten at least once -- I was one of the only exceptions, probably because I daily doused my boots in high-strength insect repellent, to the point that by the end of my trip my boots were composed of 5% shoe leather and 95% DEET.  If I ever get rid of those boots, I will probably have to file an Environmental Impact Statement.  But I didn't get bitten, unlike poor Linda, a retired nurse from Oakland who got bitten about a dozen times and constantly had large bloodstains on her socks, pants, and shirt.

One of the most curious things about Malaysia was the pervasive role of religion.  61% of Malaysians are Muslim; we saw many veiled women, and daily heard the chanted call to prayer broadcast over speakers.  But 61%, although a majority, means that there are plenty of other beliefs; there are substantial numbers of Hindus (whose brilliantly-colored temples were often seen on our van trips), Buddhists, and even a few animists amongst the Orang Asli, or aboriginal settlers of the peninsula.  But the Malaysians are, by and large, a people amongst whom the adherence to some religion is taken as given, and who have a big focus on decorum and morality.  I saw a few tourists who were showing more skin than was considered proper -- women in short-shorts, men who were shirtless -- and saw more than one skew glance being given to them.  I wore shorts on occasion (while not actively birding in the forest; wearing shorts in the Malaysian forest is like waving a sign in front of the leeches that you're open for dinner) and wondered if the tattoo on my leg would attract any negative attention.  I didn't notice any, but you have to wonder what the more conservative citizens think of some of the foreigners they see.

Last: Malaysia is far away.  It took over 24 hours in the air to get me there, and it is exactly half a day off from my home time zone; when I Skyped with my wife, in the places where wifi was available, I was always had the vertigo-inducing awareness of being on the opposite side of a giant spinning ball.  When it was day in New York, it was night in Malaysia, and we had to plan to meet -- as she was getting ready to head to work, I was getting ready to head to bed.  On the way back, I took the longest nonstop flight in the world -- Hong Kong to New York City/JFK.  Sixteen hours in the air.  And although I had no travel mishaps whatsoever -- not so much as a five-minute departure delay -- I do wish I had not been on the special Screaming Toddler Flight.  I've never been so glad to get off a plane.

So, anyway, those are a few impressions of my first visit to the continent of Asia.  I came away with an impression of a friendly people, a commitment to protecting their beautiful environment, and 199 "life birds" -- species I'd never seen before.  I survived sambal ulek and durian, and all in all, had a wonderful time.  Still, it's nice to be home, where the temperature is mild, breakfast sauces don't burn your face off, and you can walk in the woods without being bitten by leeches.