Feed the trees

How good are forests at soaking up carbon, and how much will they buffer greenhouse gas emissions and save us from climate change?

It's an extremely knotty question — and so this review (open access) of the issue just published in New Phytologist is extremely welcome. Increased CO2 should be a fertilizer, and things grow quicker in warm weather, but as temperature increases, the rate of respiration rises more quickly than the rate of photosynthesis, so the rate at which trees release more carbon rises more quickly than the rate at which they soak it up (this also has implications for metabolic ecology: by understanding these effects, via metabolic rate, you can build a bridge between cellular and individual metabolism and the workings of the global carbon cycle). Also, plant growth is limited by other things, so a lack of nitrogen, for example, may limit trees' ability to respond to higher CO2, or warmer temperatures.

The review, which looks at studies in boreal and temperate forests, concludes that we don't really know what's going to happen. Here's what they say…

It is not in doubt that newly established young forests will continue to be C sinks for the foreseeable future. The key question is whether the mature forests that are C sinks today will continue to be sinks as the climate changes. … Forest ecosystem models indicate that the additional terrestrial sink arising from global climate change is likely to be maintained in the short term (over several decades), but may gradually diminish in the medium term. … Because of current limitations on our understanding with respect to acclimation of the physiological processes, the climatic constraints, and feedbacks among these processes – particularly those acting at the biome scale – projections of C-sink strengths beyond a few decades are highly uncertain.

This seems a good argument against tree-planting carbon offset schemes.

How big can a meat-eater get?

Today's news@nature has a story by me (free for a week) about an extremely ITBOAH-esque paper on carnivore energetics and ecology by Chris Carbone and colleagues. This looks at the costs and benefits of different hunting strategies — basically, whether you eat stuff much smaller than you (as tends to be the case with small carnivores, such as hedgehogs), or whether you try and bring down things about your own size (which is what big carnivores such as cheetahs and wolves tend to do).

Eating small stuff is a cheap, low-return strategy, unable to support big carnivores — this limits the maximum size of insectivores. Eating big stuff is high return, but costly, because hunting takes a lot of energy. And it becomes more costly the bigger you get — until at about 1,100 kg, carnivores go out of business.

The largest fossil carnivores are about this size. It also suggests how evolution might paint carnivores into a corner — being big and fierce has obvious advantages, in that you're a top hunter, and you can boss your own species about. But in hard times, you starve. The fossil record seems to show high turnover for fossil carnivores, as the follow this bigger, bigger, bust pattern.

The new paper is the latest in a now quite impressive series of papers by Carbone and his colleagues building links between body size, metabolism, behaviour and population biology. Here, for example, they describe the shift in prey size described above, and here they relate body size, metabolism, prey density and predator population density.

The chances of anything coming from Mars are … 1

In a discovery sure to have major implications, a team of researchers has discovered that the laws of logic and causation are very different on Earth and Mars. The finding suggests that these concepts, often assumed to be universally applicable, may in fact vary from place to place.

"On Earth, we are used to the idea that absence of proof is not proof of absence," explains Mike Trouser, a philosopher at Madeup State University, lead author of the new research. "Similarly, just because a thing might have happened, it doesn't mean that it did happen.

"On Mars, however, we now know that these principles don't apply, and that anything not known to be stonkingly, mind-crushingly impossible must have happened."

As an example, Trouser cites a story in the Guardian on Saturday:

Microbe experiment suggests we could all be Martians

Experiments by an international team of researchers back a controversial theory that life flourished on Earth after primitive organisms arrived aboard a meteorite, itself gouged from Mars by a giant impact.

The story refers to a recent paper in Icarus, which found that various microbes and a lichen can survive being sandwiched in rock and then twanked with a steel plate, to recreate the pressures placed on known martian meteorites.

"You might think that this just shows that contemporary microbes can be twanked with a steel plate and come up smiling," says Trouser. "After all, one cannot tell from reading the abstract whether the experiments exposed the microbes to vacuum conditions, extreme temperatures or high doses of radiation." But in fact, the Guardian quotes the paper (although none of the authors, and no independent sources) as saying:

These results strongly confirm the possibility of a 'direct transfer' scenario of 'lithopanspermia' for the route from Mars to Earth, or from any Mars-like planet to other habitable planets in the same stellar system.

"A strongly confirmed possibility (whatever that is)? Please, you're being too modest," says Trouser.

Initially, Trouser was intrigued why one doesn't see similar results in any other field being reported in this manner. "One doesn't for example, regularly see articles informing us that we don't know for sure that drinking margaritas doesn't make you live longer, or that we can't be sure that cats aren't plotting to overthrow humanity," he points out. "I think the differences in Martian logic now explain this apparent anomaly."

The unique workings of Martian logic don't stop there. At the recent meeting of the American Astronomical Society, it was widely reported that the Viking landers would not have recognized — indeed, would have killed — any life form using hydrogen peroxide as a biological solvent.

The ambiguity of the Viking experiments is nothing new - they have become the grassy knoll of astrobiology. They were designed to look for biological processes — nutrient uptake, gas release — in Martian soil. All gave positive results! Trouble is, so did all nearly all (but not all) the controls. We should probably learn from the Viking experiments to try and design the next life-detectors, rather than endlessly picking over the results.

But, although he believes the existence of H2O2-based life proven, Trouser believes we should also be casting the net wider. "Never mind weird alien biochemistry," he says. "There's plenty of regular life on Mars."

As an example, he cites a 2004 article discussing the general difficulty of recognizing as alive anything that doesn't give you an anal probe and say 'Take me to your leader'. In it, referring to how better we are at spotting microbes now than then, Andrew Steele of the NASA Astrobiology Institute at the Carnegie Institution of Washington says: 'There could have been 10 million bacteria per gram of martian soil, and Viking wouldn't have seen them.'"

"What we now know Steele should have said," says Trouser, "is that there are 10 million bacteria in every gram of Martian soil. For all we know, the Viking mission missed spotting the Flying Spaghetti Monster," he adds. "Hail, then, Martian Flying Spaghetti Monster!"

Just when you thought...

...Tony Blair had exhausted his capacity to disappoint, along comes this.

Update: I admit to being confused about offsetting. I saw someone compare it to trying to combat sea-level rise by drinking more. But summing up what I've read recently, it seems that it's better not to emit at all (so flying's not ok), but that some projects can help. This piece from the Independent sets out the pros and cons quite nicely. And this from Nature($) goes into a bit more detail. The basic message is energy efficiency and renewable generation, good, trees, bad.

The owl that gathers manure

Oh dear. Having only recently pronounced the death of animal behaviour, I keep coming across irresistable papers.

“Gather ye cowpats while ye may,” it says in Fungus the Bogeyman. American burrowing owls (Athene cunicularia [isn't that a nice name?]), it turns out, take this advice to heart, collecting manure and scattering it about their burrows.

One hypothesis for this unsavoury behaviour is that the dung disguises the smell of their burrows from predators, but Matthew Smith and Courtney Conway found that manure-strewn burrows were just as likely to suffer predation as clean and tidy ones. Instead, their results suggest, the manure attracts insects and other invertebrates, which the owls eat.

Are there any other animals (besides humans) that lure prey with bait like this? I suspect there are, but none are springing to my mind.

More flimsily, Smith and Conway suggest that the manure also acts as an ‘occupied’ sign, showing other owls that a burrow is taken. What’s wrong with flowers? This is a bird with self-esteem issues. Or maybe it’s some kind of dirty protest. If only we knew what they’re demanding.

Peace breaks out (among ants)

Given that different ant species, and different colonies of the same species, are usually extremely hostile towards one another - fighting, slave making, that sort of thing - this report of a small species living peacefully, and perhaps symbiotically, in the nest of a large one is Quite Interesting. The ants live in hollow tree branches in West Africa; the small one (Pyramica maynei) is also capable of living on its own, but might benefit from the secure environment of the large species' (Platythyrea conradti) nest, possibly in exchange for keeping the place clean.

Given the choice, I'd vote for a sea lion

For a long time, I wanted to be a behavioural ecologist when I grew up. I had come to biology via watching birds and David Attenborough programmes, read The Selfish Gene (which is bascially a very good book about behavioural ecology) at an impressionable age, and in the early 90s it seemed like a really vibrant and exciting area.

But now it seems to have been a victim of that success — almost (to exaggerate) a completed science. We have a set of ideas that have been very successful at explaining animal behaviour in evolutionary terms — kin selection, optimal foraging, various models of sexual selection, and a few others. Most aspects of animal behaviour seem explicable in terms of one or other, and nothing seems to need a big new idea to explain it. I'd be interested to hear anyone else's thoughts on this (particularly if you disagree).

Anyway, this is really just a preamble before I mention some recent behaviour papers that caught my eye. Behavioural ecology might not be white hot, but it still delivers high on the fancy-that factor.

For example, did you know that sea lions are masters of self control? If you offer them a pile of five fish or a lone fish, and then give them the one they don't choose, they quickly learn to choose the smaller reward — more quickly, in fact than primates, who keep lunging helplessly for the bigger pile (I don't think they offered the primates fish. Probably bananas, or something.).

Not only that, diving seals can hold off digesting their dinner until they surface, to reduce the amount of oxygen they use up underwater.

One area of behavioural research that's still kicking up dust is, of course, evolutionary psychology. Here, for example is a worrying paper from Evolution and Human Behaviour looking at the influence of face shape on voting decision:

We show that differences in facial shape alone between candidates can predict who wins or loses in an election.

Anthony Little and his colleagues took the faces of recent election opponents — Kerry/Bush, Blair/Howard, and several others from around the world. They recreated the differences between the two candidates' faces on neutral models, so that subjects wouldn't recognize them, and then tweaked them to exaggerate the difference (not sure why they did this — it seems to undermine the study's claims to reflect reality). Then they showed the faces to people, and asked who they would rather vote for, without any other information.

The percentage preferences for the simulated faces predicted fairly well the destination of votes cast in actual elections.

The Sunday Times reported on this at the weekend.

Little speculates that voters chose Blair because his skin looked healthier than Major and his face, with a strong jaw and thinner lips, looked more masculine than Hague. “Firm jaws and heavy brows denote masculinity,” he said.

Perhaps more reassuringly, they found that "there may be no general characteristics of faces that can win votes". People asked to choose a peace- or wartime leader, for example, prefer different sorts of faces — wartime voters prefer a more dominant, masculine face, apparently. Sigh. I imagine doctors of spin are already out with the callipers and booking their men and women in for plastic surgery.

An obscenity

This is beyond the usual scope of this blog, and I know there're a lot of bad things happening in the world, but to take a group of people who came to your country to work in your medical system, accuse them, despite an overwhelming body of evidence to the contrary, of infecting children deliberately with HIV, torture them, refuse to hear relevant evidence in court, and then sentence them to death - in what mainly seems to be an attempt to cover-up the shoddiness of one's own procedures - seems particularly shameful and grotesque.

Let's hope that the Libyan government has some sense of justice and humanity, and overturns this decision.

Nature's Declan Butler has done a fine job of reporting this story.

It's lonely out here

There's an interesting post on Evolgen about the paucity of ecology bloggers. Although the discussion seems to have wandered off-message rather. I reckon that one of my previous rambles about ecology's general media-unfriendliness may be relevant to this issue.

The way things go

If, like me, you're a fan of the conservation of momentum, chemical reactions, kettles, stink, bangs, 70s board-game Mousetrap, or 70s BBC2 show The Great Egg Race, get down to Tate Modern and check out Fischli & Weiss's "The way things go' (Der Lauf Der Dinge).

This piece of video art, part of an F&W retrospective showing at the Tate until January, shows an absurdly convoluted and entertaining chain reaction of things bumping, rolling and swinging into each other, not to mention setting each other on fire, inflating, puncturing, foaming, and so on. It's not exactly science, but you can see a sort-of-science (or engineering, at least) thought process behind it that ought to appeal to anyone in the least bit geeky. It reminds me of the great domino-topples that seemed also to be on TV every week in my distant, distant youth (do they still do those?). And apparently it was ripped off by, I mean inspired, that Honda advert of a few years ago.

I didn't stay for the whole thing, which lasts 30 minutes, but what I did watch seemed to go on forever. Some of the slower parts were actually quite painful to witness. If you can't get to the Tate, don't worry. You can get a DVD (and see a trailer) here (I was sorely tempted - I envisioned showing it at Factory-style happenings in my groovy Shoxton loft, and I don't even live in a groovy Shoxton loft. Or own a DVD player.). Or you can see the first 7+ minutes on YouTube:

Make yourself happy

Thank God (or whoever else might be responsible) for the Onion.

Kansas Outlaws Practice Of Evolution.

The cost of leafing

This week's Nature has a news feature by me on leaves (why have they made 'plantecology' one word?). Specifically, it's about the patterns in leaf construction seen across all land plants, what causes them, and the consequences that they have for our understanding of the living world. (Lovers of waffle will not want to miss hearing me talk about this on the Nature podcast.)

[M]ost of the variation in the physical and biochemical properties of leaves can be represented on a single axis running, to put it crudely, from quick and juicy to slow and tough. [This is] the 'worldwide leaf economics spectrum', and it embodies many of the trade-offs that govern how plants deploy their resources within the limits that physics places on biological possibility.

The work … has attracted the attention of everyone, from plant physiologists studying how leaves work to biogeochemists looking at the cycling of nutrients on a global scale. In part, the paper is so popular because of the size and scope of the database that underlies the work; but the popularity also reflects the intellectual excitement that surrounds the discovery that so much can be explained by so little. This has given some ecologists hope that by looking at the large-scale patterns in how organisms work, they can gain a general understanding of why species live where they do, and why some are common and others are rare. Such findings are not of purely academic interest: climate researchers are using them to improve their models of the consequences of global warming.

For me, one of the most interesting aspects of writing this feature was investigating an idea among some ecologists that the best way to understand why species live where they do, and why some are common and others rare is to think not about species, but traits — such as leaf biology, seed size and number, and so on.

In some ways, this is counterintuitive. Most, perhaps all, cultures name the plants and animals around them, and recognize that they split into groups of similar kinds, i.e. species. Many ecologists come to the science through a love of natural history, and identifying and naming stuff. And consequently, many theories of biodiversity are rooted in what's been called 'nomenclatural ecology':

To try to understand things such as what determines the number of species that can coexist in a place, how numerous each species is, and how productive the system as a whole is, ecologists have traditionally looked at what species are present, how they interact, and how their abundance affects that of the others. Such an approach is an extension of ecology's roots in natural history, says Brian McGill of McGill University in Montreal, Canada. "People become ecologists because they love to go outdoors and look at the woods. They get attached to putting names on things, and get focused on knowing lots about particular organisms."

But this approach soon becomes intractably knotty, as the number of possible interactions between species rises geometrically with the number of species. "We don't have the capacity to learn as much as we need to know by studying one species at a time. Studying interactions between species, and then trying to build that up, hasn't panned out. It's too complicated," explains McGill.

Traits — such as, for leaves, mass-per-area, or photosynthetic rate — are measurable, and comparable in a way that species names aren't, and also allow one to quantify natural variation. I think of this as dropping below the species level, to look at the components of biology — how organisms work, and how they differ — and I've a hunch it might offer a way out of the current morass of different theories to explain the origin and maintenance of biodiversity. Of which there are tons — it did my head in trying to get to grips with this area.

Of course, to make satisfying science, one wants to be able to turn trait studies back into predictions about species, because as human beings that's how we perceive the world.

But this looks like it might be possible — Science recently published an extremely cool paper by Bill Shipley and colleagues using trait measurements and, to my satisfaction, maximum entropy theory to predict the abundance and distribution of plants in abandoned French vineyards with 94% accuracy. Which is pretty damn good.

I confess, I really should have covered this in ITBOAH, but it didn't cross my path while I was writing this. Very sorry, ITBOAH-readers.

Review: Genes in Conflict

I've got a piece (registration required) in the current London Review of Books on Genes in Conflict by Austin Burt and Robert Trivers.

The book's a brilliant resource, bringing together what must be pretty much every piece of information on selfish genetic elements, such as transposable elements, selfish sex chromosomes and imprinted genes. These genes can thrive at the expense of the organisms that carry them, causing conflict and selection to operate within genomes and organisms, as well as between them.

Such conflict has led to some extremely odd biology (such as the sperm that can eject the maternal chromosomes from the eggs they 'fertilize'), some extremely fundamental aspects of our biology (such as the uniparental inheritance of mitochondria, and probably some details of mitosis and sex itself), and some extremely interesting potential effects on our behaviour and psychology, caused by different bits of the genome pulling in different directions. I imagine this will be explored further in Trivers' next book, which is apparently going to be about the evolution and uses of self-deception.

This is the sort of book that would work splendidly as an online resource — it doesn't take a linear approach (early on the authors say it can be read in any order, which is a bit dispiriting for a reviewer settling down to read the whole thing), so hyperlinking would be valuable. And this is such a fast-moving field that regular updates would be welcome (such as, say, the power of transposable elements as a creative force in evolution, which is a bit off-message from the book's main thrust, but an exciting area, as a recent N&V feature (registration required) in Nature shows). Magisterial overviews such as this still clearly have a place on academic bookshelves, but they need to cope with the way that the internet has made the information they collate easier to find and access.

Leonardo's notebooks

Anyone interested in science would do worse than go to the Leonardo da Vinci exhibtion at London's V&A museum, running until 7 January. I went last week.

The exhibtion, of material from the man's notebooks isn't primarily an aesthetic experience (although there are some beautiful things there). What it's about is giving you an insight into Leonardo's thinking, and the full range of his preoccupations.

Nowadays, the term 'Renaissance man' is applied to any science PhD who's read a novel and got grade 3 clarinet (women tend to do lots of different things without running around giving themselves grand names). This exhibition shows you better than anything I've ever seen what being a Renaissance man really meant. Leonardo treated the artistic, scientific, mathematical, biological, architectural, mechanical, you name it, as all one and the same - often on the same sheet of paper. Designs for musical instruments are alongside those for palaces, and stage sets, which are alongside plans for epic murals, or engines of war, or anatomical drawings, or clouds. Astonishing.

On the science side, it looks very much as if he was thinking about problems, such as finding a shape's centre of gravity, or a volume's solid, that were solved by Newton/Leibniz's invention of calculus. He also seems to have pondered other Newtonian stuff, such as gravity and mechanics. (And he tried to square the circle, and build a perpetual motion machine. Nothing I could see on thurning base metals into gold, though.)

He also did some drawings on the form of trees, river networks, and blood vessels that (looking at things with a biased eye, I admit) intriguingly prefigures the network models of metabolic rate, river networks, and other stuff by West et al. and Banavar et al.

And here's a quote, presented in the exhibition, which could have come straight out of D'Arcy Wentworth Thompson's mouth, and which sums up world view (one of them, anyway) I write about in ITBOAH:

"A bird is an instrument working according to mathematical law."

Pegged to this exhibtion, there's an interesting piece by Guardian art critic Jonathan Jones on how the notebooks ended up in the hands of the British royal family.

Is natural selection a law of physics?

More on applying the physics of statistical mechanics and thermodynamics to ecology and evolution. This paper by Guy Hoelzer and colleagues appeared recently in the Journal of Evolutionary Biology:

On the logical relationship between natural selection and self-organization

…In this study, we attempt to describe the logical framework that relates the general process of self-organization to the specific process of natural selection. We describe natural selection as a mechanism that coordinates the coevolution of species in an ecosystem to effectively capture, process and dissipate solar energy into the earth’s shadow. Finally, we conclude that natural selection is an emergent process founded on the same thermodynamic imperatives that are thought to underlie all self-organization. This perspective suggests … the possibility that there may be a physical basis for understanding the origin of the process of natural selection. Rather than being merely a fluke of nature, the origin of natural selection that may be driven by energy flows across gradients.

As an example of the kind of links between biology, thermodynamics, and self-organization that they are pursuing, Hoelzer et al. give photosynthesis. They point out how good it is at levelling out the gradient of solar energy, and suggesting either that "photosynthesizing life is a statistically favoured component of the biosphere, or that a high-flux channel for light transduction is a favoured endpoint, towards which perturbed ecosystems recover. Physical principles expressed in terms of stable end states imply a natural teleology, which we have suggested (somewhat imprecisely) is the reduction of the spectral and spatial energy gradient imposed by the situation of earth in a solar radiation bath."

They also invoke metabolic scaling theory, which explains living things' energy use in terms of the geometry of transport networks (something similar seems to apply to the geometry of lightning strikes and river basins), and suggest that a taking a self-organizational view is a good way to try and understand why, the more energy an organism uses (whether metabolically, or, for humans, in society), the fewer offspring it has. (More about all this here and in ITBOAH

Other striking quotes:

We offer the conjecture that the truly ultimate explanation for any dynamical event, and the qualities of any emergent dissipative structure, including organisms and ecosystems, is thermodynamic.

Natural selection is to self-organization as language is to communication. Language is not synonymous with communication, yet it is a quantum leap forward in communicative effectiveness. It is also not merely a more complicated for of simpler modes of communication. … Language has emerged from the drive to communicate just as natural selection has emerged from the drive to break down gradients.

Much of this is not particularly new. Dynamic, complex physical systems can take on orderly, structured states, and physicists such as Stuart Kaufmann have long suggested that the same principle applies to living things — that self-organization, as well as, or instead of, natural selection, can explain the complexity and structure of life.

Likewise, it's not a new idea that thermodynamics can explain the structure of life, and that this structure evolves to flatten out energy gradients as much as possible, and degrade energy/produce entropy as quickly as possible.

And biologists have usually resisted these concepts. Natural selection is so successful that bolt-ons from physics seem superfluous. There's no reason to believe that natural selection should maximize anything thermodynamic, and many biologists take issue with the assumptions and predictions of this approach. Someone once pointed out that the reason horses had evolved was to make more horses, not to make horse manure. John Maynard Smith thought harder about these things than most biologists, and (I think) remained sceptical. (Try here or here.)

So either all the current upsurge of this stuff is just a cyclic blip, or we're really inching towards some kind of new insight. I'm not sure which.