NEW VOICES: the science of twilight

NOTE: Alex Morgan's example has inspired another of my students, Danna Staaf, from the Santa Fe Science Writing Workshop to write up her ruminations on -- how shall we say this? -- the "found science" of plant biology and biogeography in the book/film series Twilight. Yes, Stephanie Meyers and her uber-emo sparkling vampires can inspire a young marine biologist in surprising ways. Danna has her own blog, the Cephalopodiatrist -- hey, the girl loves her squid. PZ Myers would be so proud. Danna is spending this summer in San Diego "sorting tiny squid out of jars of plankton and getting woozy off ethanol fumes." Good times!

"Have you read Twilight?" was the first question from the lips of my thirteen-year-old stepsister last Christmas. Answered in the negative, she gushed, "Oh my God oh my God you have to read it! It's so good!" and handed me the first book of Stephenie Meyers' teen vampire romance series.

At her age, I was a gamer geek, so my exposure to vampires came through White Wolf role-playing games. (It would appear that I entirely skipped the whole Buffy phenomenon, an admission which I realize is tantamount to heresy in this company. Assuming Jennifer ever forgives me and allows me to try another Twilight biology class, I plan to act on her suggestion of positing a plausible mechanism for vampire sparkle.) I was interested to see the newer generation's perspective on the subject. Not too surprisingly, things have changed. I don't have much to say about the book itself--I devoured it in a matter of hours and would never recommend it to anyone. If that combination of insinuated praise and censure is too confusing to parse, well, never mind. I'm no literary critic, just a biologist.

However, as such, I was delighted to find Bella and Edward meeting as lab partners in high school biology. They are by far the best students in their class, and I figured that might be some inspiration for their zillions of adoring fans to brush up on their own science skillz. To that end, I (rather ambitiously) present this Twilight-based lesson in plant biology, in order to answer the burning question: Forks and Phoenix: Why is one green and the other brown?

Bella Swan hates Forks, Washington. It's too cold, too wet, and just too green. Day after day she sloshes through the moss and mud, shivering and dripping, dressed in brown to remind herself of home: warm, dry Phoenix, Arizona. She's a smart cookie, so it's a bit odd that she never stops to ponder why Forks is green and Phoenix is brown. Think about it, Bella -- isn't it strange? Why such herbacious profusion in your father's town, such sparse shrubbery in your mother's?

The youngest schoolchildren can usually chant a plant's basic needs: "Light and water!" Along with carbon dioxide, these are the ingredients of photosynthesis, that remarkable trick of natural alchemy whereby plants seemingly create something from nothing. With these common household items, plants construct their own bodies and directly or indirectly feed most life on Earth.

However, it's a bit more complicated than that. While carbon dioxide is ubiquitous, light and water are not distributed evenly around the planet. In the average year, Phoenix collects a meager 8 inches of rain but 325 days of sunlight (that's almost 90% of the year), while Forks brings in a whopping 120 inches of rain and coyly refuses to tell me how many days out of the year it sees the sun. (Nearby Quillayute gets 209 days of rain -- well over half the year--which doesn't account for merely overcast days.) In any case, Forks certainly owns the dubious distinction of being the wettest town in the lower 48 (for trivia buffs: apparently the island of Kauai is wetter). Obviously, the more rain you get, the less sun, and vice versa. This represents a frustrating tradeoff from the perspective of a plant: Forks is wet but dark, while Phoenix is dry but sunny. A vampire's choice of hometown may be a no-brainer, but if you're a plant, how do you decide?

The thing is, it's a false tradeoff. Some light makes it to the earth's surface even on the cloudiest day -- as you may have noticed if you're prone to sunburn. So plants can cheat on the sunlight, but there's no cheating on water. Think of Star Wars' Tatooine, where Uncle Owen and Aunt Beru have a farm on a desert planet. The only way they can manage is with the help of "moisture vaporators" gathering water from the air. This isn't necessarily as crazy as it sounds; even desert air has some water in it. Standard humidity in parts of Arizona is 50%-23%, morning to afternoon. But without the help of science-fictitious vaporators, plants can't gather that water themselves, any more than you could take a drink out of the air.

In fact, plants are constantly losing water to the air, through evaporation from little pores called stomata, which are like combination nostrils/sweat glands/tiny hearts. No really, bear with me! Like nostrils, they provide the plant with air (although the gas of primary interest to plants is carbon dioxide, not oxygen). Like sweat glands, they allow water to evaporate from the "skin" of the plant. However, while animals use evaporation as a cooling mechanism, plants use it to drive their circulation -- hence the third role of the stomata as tiny hearts. They are not muscular pumps like our hearts, but passive pumps dependent on capillary action--the propensity of water molecules to stick together. As one molecule evaporates, it draws the water behind it towards the surface, which in turn evaporates and pulls more water behind it, resulting in a slow, steady upward movement of both water and nutrients from the roots to the leaves.

To sustain all this breathing, sweating, and pumping (hot vegetable action!), plants need either abundant water at their roots or a low rate of evaporation from their leaves. Forks, with its heavy rainfall and high humidity, offers both. If Bella tried to bring any plants from Forks back to her yard in Phoenix (unlikely, I know, but let's just imagine) they would quickly dry up and die, victims of a double-whammy: little water and fast evaporation.

A few desert-loving plants have solved this problem, dotting the Phoenix brownscape with sparse but determined scraps of green. Some plants, like the four-wing saltbush, recruit a special little enzyme just to grab carbon dioxide out of the air. It is very good and very fast, so plants don't have to leave their stomata open as long, and they don't dry out as quickly. If your lungs were extra especially good at pulling oxygen out of the air, you wouldn't have to breathe as much (and your nose wouldn't get so dry in the summer).

Hiring an extra enzyme is a rather messy hack, though, and it turns out there's a neater solution. The real champion desert plants, like cactus and agave, have simply decoupled their need for carbon dioxide and their need for light. At night, when the air is cooler and evaporation slower, they open their stomata, breathe in a big reserve of carbon dioxide, and store it as a semi-processed acid. During the day, they keep their stomata tightly closed to prevent excess water loss, but drink in all the sunlight they need to finish processing that stored carbon dioxide. When the sun goes down, rinse and repeat.

The result of all this photosynthetic finagling is two very different ecosystems: the Sonoran desert and the Hoh rainforest. That's right, Forks is in a rainforest! I bet you thought all rainforests were tropical, but it turns out they're not. (I bet you thought all rainforests were wet, too. I sure did, until I went to Eastern Australia and learned about dry rainforests.) Desert plants tend to be both less diverse (fewer species) and less abundant (fewer individuals of each species) than rainforest plants. The ecosystems in question are built on their plants, so Forks supports a correspondingly more abundant and diverse food web than Phoenix -- all the way up to the big predators. The Hoh rainforest, as the Cullens can tell you, is home to plenty of bobcats, cougars, and bears. The Sonoran desert seems stark and barren by contrast, boasting no more than a handful of lean brown coyotes. Little ecological wonder that Forks sustains not only a family of vampires, but a pack of werewolves, too!

Coda: Pretty awesome analysis, right? We look forward eagerly to Danna's ruminations on why the vampires in Twilight sparkle. In the meantime, in closing, we offer the following mashup of scenes from Twilight and Buffy the Vampire Slayer currently making the rounds on the Interwebs. Nothing against Stephanie Meyer fans, but it's pretty obvious that Buffy, with her snarky irreverence, would have totally kicked Edward's broody butt. We're just sayin'...

Comments

[florian.idelberger@gmail.com]

haha. that video is awesome :)

[Alex Morgan]

Great post, Danna! I tried to image an ANIMAL with combined set of nostrils, sweat glands, and heart. Something like a big beating nose that sweats. That was in Monty Python, wasn’t it?

[Danna Staaf]

Thanks for adding the hilarious video! It actually brings up a curious bit of social science. Buffy claims that "being stalked isn't really a big turn-on for girls" but Bella might disagree. Both heroines are, of course, media constructions, and their divergent opinions seem to typify media schizophrenia on this issue.

I found a neat article ( http://people.stu.ca/~mccormic/3263/articles/Stalking2002.pdf ) in the Journal of Criminal Justice and Popular Culture called "The Media Construction of Stalking Stereotypes," in which the authors argue that media sensationalism played no small part in elevating stalking to a crime despite a lack of evidence (at the time) for its widespread prevalence or danger. However, "At the same time the media horrify stalking, the media ironically tend to glorify stalking-like actions" by portraying persistent, determined pursuers as the heroes of romantic narratives. Such idealization, they say, makes recognition of real-life stalking behaviors more difficult.

So if Bella romanticizes persistence, and Buffy criminalizes it, do they cancel each other out? In the very best academese, the authors admit that "to characterize any tendency in the media as a whole is a process fraught with ironic potential."

[Calvin Goodrich]

Strictly speaking, Owen and Beru Lars were farming FOR the water. They then sold off what they collected. But they weren't growing anything (except possibly for their own use.)

[Hobbes]

"But without the help of science-fictitious vaporators..."
Or you could use try an atmospheric water generator which works pretty much like a scaled-up dehumidifier.
http://en.wikipedia.org/wiki/Atmospheric_water_generator

[Danna Staaf]

Thanks for the extra info, Calvin and Hobbes! C: The Wikipedia entry on Tatooine claims that "moisture farmers harvest water vapour from the atmosphere, and use it to grow crops in underground hydroponic labs" so perhaps there is some controversy on this subject? H: Or an air well! http://en.wikipedia.org/wiki/Air_well_(condenser) My favorite fun fact from that article is that there exists an "International Organization for Dew Utilization."