FINAL RESULTS: Race to Read for International Literacy Day

International Literacy Day is September 8. I've decided to participate in the Greater Pittsburgh Literacy Council's fundraising event: Open Up a Book, Open Up a Life.

Here's what I have in mind:

I will read as many books as I can between now and September 8. I'll keep a record of the books I finish here in this post. If you'd like to make a donation, pick an amount to donate per book I read. After September 8, come back here to find out how many books I've read. Do the multiplication to figure out your total donation, then go to my donation page and make a secure online donation. (Or, if you'd prefer to donate through the mail, just let me know.)

(Of course, if you'd prefer to just make a single fixed donation, you can do that through the donation page, too.)

You can donate any time between now and September 30. GPLC's tax ID number is, I believe, 25-1392652, if your company can make matching donations. [h/t to Erin for reminding me to look this up!]

If you're not able to make a monetary contribution, please consider donating some time to GPLC or to your local literacy group. Or, just pass the word along to others.

Thank you!

BOOKS I'VE READ:

1. The Good That Men Do (Andy Mangels and Michael A. Martin)
2. What Einstein Told His Cook: Kitchen Science Explained (Robert L. Wolke)
3. Kobayashi Maru (Michael A. Martin and Andy Mangels)
4. Proust and the Squid: The Story and Science of the Reading Brain (Maryanne Wolf)--Recommended!
5. Holy Hullabaloos: A Road Trip to the Battlegrounds of the Church/State Wars (Jay Wexler)--Recommended!
6. Prime Directive (Judith and Garfield Reeves-Stevens)
7. Speaking Up: The Unintended Costs of Free Speech in Public Schools (Anne Proffitt Dupre)
8. Memory Prime (Gar and Judith Reeves-Stevens)
9. A Suitable Vengeance (Elizabeth George)
10. When Gay People Get Married: What Happens When Societies Legalize Same-Sex Marriage (M.V. Lee Badgett)
11. The Kobayashi Maru (Julia Ecklar)

Usage tip: everyday vs. every day

This one crops up so often, it's practically an everyday occurrence. (ha, ha, ha...sorry.)

Here's the difference between everyday and every day:

Everyday is an adjective.
Every day is an adverb.

But that doesn't really matter. You want to know how to use them correctly, right? Here's a handy rule of thumb:

If you can replace the term in your sentence with occasional or frequent or any other adjective and have the sentence still make grammatical sense, chances are you should be using everyday. If you can replace the term with Tuesdays or sometimes, you should probably be using every day.

For example:

WRONG
This shampoo is best for every day use.
Everyday, I walk my dog.
People should try to exercise everyday.
Luckily, loud street arguments are not an every day occurrence in my neighborhood.

CORRECT
You can use this shampoo every day.
Some trainers say you should run every day, but I think that's too much.
He's trying to prove that he's an everyday guy.
Let's try to make laughter an everyday event.

The mystery of the rotating seeds

If you live in a temperate deciduous climate, you probably know what a maple tree is. And if you’ve been in a maple forest during spring or fall—or, really, any time of year—you’ve probably seen maple seeds. They look a bit like badminton birdies, only flattened: a heavy, solid "nut" at the bottom, with a single "wing" above. The wing helps the seed fly relatively long distances (for a plant)—up to a few kilometers in some cases.

A maple seed. From http://commons.wikimedia.org/wiki/File:Maple-seed.jpg.

Watching a maple seed fly is an interesting experience—they flutter and twist very rapidly. Because they twist and spin as they fall, scientists say they autorotate. In fact, they autorotate quite stably—a factor that allows the wind to carry them far from their parent trees.

Maples aren't the only trees with autorotating seeds—hornbeams, for example, have similar winged seeds. In all of these seeds, the autorotation is thought to help create extra lift on the seed, enabling it to travel farther from the parent tree. (Rambling offspring are a benefit for plants, because plant seedlings compete with surrounding plants for soil nutrients, sunlight, and water. If they land too close to the parent tree, they end up competing with their own parents—which benefits neither parent nor offspring, and therefore is detrimental to the survival of the species.)

Maple seeds and other autorotating seeds produce surprisingly large amounts of lift as they fall, considering how small and relatively slow they are. This is similar to the wings of many insects, which can produce a lot of lift from a relatively small surface area. Insect wings create this lift through the production of a leading edge vortex (LEV)—that is, a maelstrom of disrupted air along the edge of the seed that is "cutting through" the air as the seed falls. (Think of a wing—one edge of it is pushing through the air as it moves forward. The other edge trails along behind. The edge cutting through the air is the leading edge.)

In the 12 June issue of Science, Lentink et al report results of an investigation into the motions of maple seeds as they fall. Because the LEVs generated by insect wings help the insects produce significant lift, the researchers reasoned that maple seeds might produce similar LEVs.

Maple seeds are relatively small, and studying them while they fall can be challenging. This is especially true if one is interested in observing the flow of air over and around the seed as it falls. Therefore, as an initial test, Lentink et al built a scale model of a maple seed that was somewhat larger than a real seed. To make studying the movement of the air over the seed easier, they attached the model seed to a large arm inside a tank of mineral oil.

It may not be immediately clear how putting a model seed in mineral oil can be used to study the flow of air around a real seed. It turns out that this works because air and mineral oil are both fluids—substances that can flow in response to stress (pressure). As it happens, all fluids behave pretty much the same way under specific kinds of stress, provided that their differences in viscosity (resistance to flow, or thickness) are taken into account. The main difference viscosity makes is in the force required to move through the fluid—as you know if you've ever tried to walk under water. The more viscous the fluid, the more force is required to push through it, and the more slowly it returns to its original position. This latter property is the reason that many fluid dynamics studies are performed in oil or water, rather than air: the higher viscosity of a liquid makes observing its flow paths much easier. The path the liquid follows around the object is the same as the path that air would follow, so the results of the study are easily transferred to air.

Lentink et al used digital particle image velocimetry (DPIV) to make an image of the fluid flow around the model seed as it "fell" through the oil. DPIV is a technique that uses laser light, high-speed cameras, and computer integration to determine the velocity (speed and direction) of the fluid moving around an object in various locations. In DPIV, tiny particles are suspended in the fluid. During the experiment, as the fluid is moving, rapid flashes of laser light shine on the fluid, making the suspended particles visible for brief instances. A high-speed camera photographs the particles during each flash. The images are fed into a computer, which analyzes the locations of the particles during each instant. Because the computer knows the location of each particle at specific instances in time, it can calculate the velocity of each particle over time. Once the computer has calculated the velocities of the particles, it can create a three-dimensional image of how they move (and, by extension, how the fluid moves).

Using DPIV, Lentink et al identified a very pronounced LEV along the model seed. To confirm that their model seed accurately represents real seeds, they placed real maple seeds in a vertical wind tunnel. They adjusted the wind speed in the tunnel so that it matched the air speed the seeds would experience as they fell. As a result, the seeds hovered in place, but still spun the same way they would if they were actually falling. They recorded the motions of the seeds as they rotated. They were also able to create images of the flow of air around the seeds. The experiments with the real seeds confirmed the results seen in the model studies: maple seeds do, indeed, produce significant LEVs as they fall.

By comparing the maple seeds to other plant seeds, Lentink et al showed that the rotation of the maple seeds, and the resulting development of the LEVs, allows maple seeds to fall more slowly than non-rotating seeds of a similar wing loading (wing loading is the ratio of seed weight to surface area). Therefore, maple trees (or hornbeam trees, or other trees with rotating seeds) can produce heavier seeds (which can contain more food for the embryonic tree), but those seeds can still travel far enough from the parent trees to avoid competition.

Maple and hornbeam trees are not the only organisms to make use of the extra lift provided by LEVs, though. Hovering insects, bats, and possibly some birds also benefit from the production of LEVs along their wing edges. It makes me wonder whether "winged" marine organisms might generate similar vortices along their wings as they "fly" through the water.

Lentink, D., Dickson, W., van Leeuwen, J., & Dickinson, M. (2009). Leading-Edge Vortices Elevate Lift of Autorotating Plant Seeds Science, 324 (5933), 1438-1440 DOI: 10.1126/science.1174196

Normally I'm against Twitter, but...

...in this case, I think I'll make an exception:
(see the original at PHD Comics.)

Calling PA residents!

If anyone who reads this blog is a resident of Pennsylvania, please contact your senator and representative today to ask them not to cut state funding for public libraries. Public libraries provide important services to those most in need during tough economic times: students, the elderly, the un- or under-employed, and other underserved populations. Many public libraries provide assistance with education and job searches. They provide free entertainment in the form of books, magazines, music, and videos. Many host tax preparation workshops, educational seminars, and social activities for seniors, children, non-native-English speakers, and the disabled.

Public libraries rely on public dollars to stay in operation. If you live in Pennsylvania and have ever used, might ever use, or know someone who uses, a public library, please write to your state congresspeople today.

If you live in an area served by the Carnegie Libraries of Pittsburgh, please attend one of the town hall sessions they are holding to determine "...the future direction of public library service to the community of Pittsburgh" (quoted from an email I received today):

WHO: Hosted by the leadership of Carnegie Library of Pittsburgh and moderated by representatives from the League of Women Voters of Greater Pittsburgh.

WHAT: A brief program will be presented outlining the financial situation faced by Carnegie Library of Pittsburgh. Individuals are encouraged to comment about Library services.

WHEN & WHERE:
Thursday, July 16 at 7:00 p.m.
CLP - Main; Lecture Hall, 4400 Forbes Avenue

Saturday, July 18, at 10 a.m.
Carrick High School; Auditorium, 125 Parkfield Street

Tuesday, July 21 at 7:00 p.m.
CCAC-Allegheny Campus; SSC Auditorium, 808 Ridge Avenue

As a library volunteer, I thank you!

Scientia Pro Publica 7

...is now available at Greg Laden's Blog. Check it out!

Good news for paleontologists?

Paleontologists, as most folks know, study fossils (or, more generally, the evidence of past life of any kind). By examining the types and distributions of fossils in rocks of various ages, paleontologists can give us insight into how life on Earth has evolved. Thanks to the study of fossils, we know, for example, that Cambrian oceans were full of trilobites, that the Mesozoic Era was dominated by giant reptiles, and that giant "terror birds" once roamed South America.

Yes, fossils are undoubtedly vital to our understanding of life on Earth. However, although fossils are the only evidence we have for the existence of past life, they have--like all evidence--limitations. Foremost among these is the preservation bias. There's a reason nearly all the fossils you'll see in a museum or private collection are fossils of shells, bones, and teeth: hard parts are much more likely to fossilize than are soft parts.

This means that critters like the sea squirt and the cuttlefish, cute though they may be, are unlikely to appear in the fossil record. Their bodies are entirely (or almost entirely) made of soft tissue, which decays rapidly once they die. About the only way soft tissue can be preserved is through mummification or other direct preservation methods; and they are pretty darned uncommon.

Size and depositional environment also play a role in preservation bias. Larger body parts may be more likely to be preserved and fossilized than are smaller body parts, because it takes large parts longer to break down (thus allowing them more time to be buried and mineralized--although this isn't a hard-and-fast rule). Similarly, critters that die in the water are much more likely to be preserved, because they're more likely to be buried before they decay completely.

Ultimately, preservation bias means that our understandings of life on Earth are inevitably biased toward largeish, ocean-dwelling animals with shells, bones, and/or teeth. This is why we know so much more about trilobites than we do about, say, ancient jellyfish.

Of course, paleontologists acknowledge this problem, and make attempts to compensate for it. One way to try to compensate for preservation bias is to use so-called "live:dead" ratios. For example, suppose in a particular ocean ecosystem 30% of the animals are bivalves, 25% are bony fish, 35% are crustaceans, and 10% are "squishies" such as anemones and jellyfish. That critter composition is known as a "live assemblage" or a "life assemblage" for that ecosystem. (I made up those numbers. They probably bear almost no relation to realistic numbers--and those particular types of critters may not occur together. Just bear with me for the sake of demonstration.) To try to correct for preservation bias, a scientist might count the number of dead critters in each category. (I should note that this type of analysis would be based on numbers of individuals, not numbers of remains--so two clam shells would count as one clam, for example.) This "dead assemblage" or "death assemblage" can then be compared to the life assemblage to figure out relative preservation rates. If, for example, 30% of the living critters are bivalves, but 40% of the remains are bivalve remains, then bivalves would have a higher preservation rate than other critters in the ecosystem.

Potential problems with this method are probably obvious: How do you know which types of modern environments to compare ancient remains to? How do you know that preservation rates in remains are the same as fossilization rates? How do you know preservation rates for different types of critters are the same today as they were then? What happens if the ecosystem changes rapidly--do the death assemblages still accurately reflect the life assemblages?

In the May 22 issue of Science, Western and Behrensmeyer present data that may help to address the last two of these questions. They used a 40-year record from the Amboseli ecosystem in Kenya to study the relative preservation rates for large mammal (15 kg-4000 kg) bones. Previous studies have shown that the life and death assemblages for these mammals are similar at specific points in time; that is, at a given time, the proportions of different species in the life assemblage are similar to those in the death assemblage.

A variety of factors have caused the Amboseli environment to change quite rapidly since the 1960s. Woodlands have shrunk, grasslands have expanded, and swamps have doubled in size. These environmental changes, in addition to direct human actions, have substantially affected the mammal populations in Amboseli during that time. The ratios of different types of organisms--grazers vs. browsers, for example--have changed as a result, and overall species diversity has declined.

Bone and live animal surveys were conducted during two time periods: 1975-1976 and 2002-2004. The bones studied during those times could be separated into subintervals based on how long ago the animal died; this allowed the researchers to divide the samples into four subintervals (1964-1969, 1970-1976, 1993-1998, and 1999-2004). They also used census data to determine the numbers of live animals in various groups during those same time intervals.

For each of the time periods, the researchers compared the proportions of different organisms in the life assemblages with those in the death assemblages. They used these data to determine how well the death assemblages "track" or represent the life assemblages. What they found is pretty interesting:

Statistically significant correlations between live populations and bone counts for the different time intervals indicate that organisms that make up a larger fraction of a living community also make up a proportionally larger fraction of the bone assemblage for that community. In other words, at least for this ecosystem, you can use the death assemblage as a pretty direct proxy for the life assemblage--if 50% of the individuals represented by the death assemblage are medium-sized grazers, then you can infer that about 50% of the organisms in the ecosystem (on average) over the time period you're looking at were medium-sized grazers. You can also use the death assemblages to study how populations in the ecosystem changed over time; the ratios of grazers to browsers in the death assemblages roughly paralleled those in the life assemblages for the same time period. They were able to distinguish changes in population composition over time scales as small as 5 years; they were even able to "predict" ecological structure from the death assemblages (and those predictions were largely confirmed by the life assemblages).

Western & Behrensmeyer's data could be very useful for paleontologists, particularly large-vertebrate paleontologists; the data suggest that bone distributions in death assemblages can be used to infer population and community structures for ancient ecosystems. With some assumptions about ecolosystem properties, bone assemblages can also be used to infer other properties of ancient ecosystems, such as species richness and productivity.

Obviously, these data have limitations; Amboseli is a relatively dry terrestrial ecosystem populated by relatively large mammals, so it's not clear whether the same correlations apply to marine ecosystems, wetter (or drier) terrestrial ecosystems, or to those inhabited primarily by smaller organisms or invertebrates. Additionally, because all of the remains studied were relatively recent (40 years isn't long enough to produce fossilization or even significant burial in most terrestrial ecosystems), it's not clear how the processes of preservation, burial, and fossilization might affect the death assemblages. (Although they do note that partially buried bones--a "pre-fossil" assemblage--seem to show the same correlations as unburied remains.) But studies like these are still very important in determining the error bars (accuracy) of ecosystem studies based on fossil assemblages.

Their data also suggest that studies of death assemblages in modern ecosystems can be of use to scientists studying the effects of human actions and other phenomena, as well as to those wishing to confirm (or obtain) estimates of vertebrate population sizes and compositions.

Western, D., & Behrensmeyer, A. (2009). Bone Assemblages Track Animal Community Structure over 40 Years in an African Savanna Ecosystem Science, 324 (5930), 1061-1064 DOI: 10.1126/science.1171155