Wednesday, February 28, 2007

A GUT of ecological scaling?

OK. I'm not going to pretend that I grasp the details of this, but here goes.

A recent paper in Physical Review Letters by Jayanth Banavar et al. presents a general theory of (macro)ecological scaling.

That is, they offer a common explanation for patterns such as that between the area of a place and the numbers of species that live there, area and total biomass, the number of organisms and species of different sizes, the maximum body size of the biggest species in an ecosystem (see here for another view of maximum carnivore size), and relative abundance — the spread of rare and common species.

All these scaling patterns seem to follow power laws, at least over partially. That is, they take the form y=ax^n, and plot as straight lines on a log/log graph.

Here's the abstract:
Scaling provides an elegant framework for understanding power-law behavior and deducing relationships between critical exponents. We demonstrate that scaling theory can be generalized to develop a framework for the analysis of diverse empirical macroecological relationships traditionally treated as independent. Our mathematical arguments predict links between the species-area relationship, the relative species abundance and community size spectra in excellent accord with empirical data.

As far as I can tell, Banavar et al. present a scaling hypothesis, based on a probability distribution of the mass and abundance of different species. Using this, and a set of reasonable assumptions (such as, that an ecosystem's total population and mass is proportional to its area) they derive the relationships described from a single starting point.

Blimey. If all these things can be brought under the one roof — this is the first such attempt that I know of — that's a big deal, I think. These are fundamental ecological parameters. Together, they pretty much sum up most of the questions that community ecology seeks to answer. Even the metabolic ecology models of West et al. (with which I am more familiar) have steered clear of tackling the relationships between species diversity and area, and between body size and diversity and abundance.

But, although much of the criticism of metabolic ecology focuses on its generality, Banavar and his colleagues have an interesting history of seeking yet more general models for the scaling of metabolic rate with body size. Banavar has also worked with Steve Hubbell to develop the neutral ecological theory. It's interesting that this is in PRL. I wonder what a biology journal would have made of it.

Thanks to Phil Ball for bringing this to my attention. I think. If anyone has any thoughts on this, I'd love to hear them.

Tuesday, February 27, 2007

Oekologie blog carnival

Just a reminder that this blog will be hosting next month's round of the Oekologie blog carnival. This follows the grand jobs done so for by Infinite Sphere and Perceiving Wholes.

So, for the period of Feb 15-March 14, please send me your favourite ecological and environmental blog posts by following this link. And I'll bring it to the world's attention, or at least that subsection of the world that reads this.

Thursday, February 15, 2007

Review: Measuring the world

I'm still recovering from the Just-Science exertions of last week, but I have got a review of Daniel Kehlmann's Measuring the World in this week's Nature ($).

They asked me to do this because I write a bit about one of the book's central characters, Alexander von Humboldt, in ITBOAH.

As a rule, I'm not really into historical fiction, or magic realism/postmodern whimsy. But I rather liked MTW (which has been a huge success in German). And I liked it more as it went along.

If you'll forgive me for quoting myself:
Kehlmann tells his story in a relentless deadpan, which is at first alienating but then gets under the skin. As the story develops, your sympathy for the two men grows, as their own does for each other. [He] does a good job of capturing the strangeness and comedy of science, as well as the powerful sense of futility that can afflict researchers from time to time.

Friday, February 09, 2007

Just Science day 5: Kill and cure?

The best way to protect an endangered species might be to ... cull it.

That's the conclusion reached by Michael Bode and Hugh Possingham in a theoretical analysis published recently in Ecological Modelling. The problem that they address is the tendency of some species to show boom-and-bust population dynamics. This seems a particular feature of tightly linked predator-prey systems: if predator is rare, prey booms, predator has lots of food, predator booms, prey crashes, predator starves, predator crashes, and so on. The Canadian lynx-hare system is the most famous example.

At the bottom of the cycles, population sizes might be so small that either predator or prey is highly vulnerable to extinction - by some other event, such as disease or disaster.

Bode and Possingham model various options for damping these cycles by removing some predators, prey, or both, from the system. "Remarkably," they say, "if the interventions are enacted at the appropriate time, infrequent culling of a small number of individuals significantly reduces the probability of extinction of the predator."

My first thought when I saw this, was that we probably rarely know enough about a species' population dynamics to know when the best time to cull is, and that such a move would be politically untenable. But, as Bode points out, the most likely candidates for such a move are large game-park species, such as elephants, about which we know quite a lot. It's also heartening that their (as they say, simplistic) simulation suggests that culling prey (which would be plants for elephants, I suppose) is more likely to be effective than predators, and that culling would be needed only rarely.

They conclude:

Most current methods of ecosystem control attempt to keep a single species population below a certain threshold, or between fixed bounds, leading to highly inefficient management. Furthermore, unnecessarily high levels of culling can generate considerable public opposition. Given the clumsy nature of such static controls, this view may be reasonable. Our dynamic control solution has the substantial benefit of minimising the preventable culling of organisms, and being extremely cost-effective.

I swapped e-mails with Bode, and besides mentioning that, in parks with very high elephant densities, such as Kruger, culling elephants seems 'almost unavoidable' (the issue seems to have flared up most recently in late 2005, judging by this BBC story), he also mentioned that similar issues were arising in Australia regarding koalas and kangaroos. As he says, why is it always the cure animals?

All I can say is I'm glad I don't have to make these decisions. Culling animals is clearly a terrible business - particularly for long-lived, highly social species such as elephants. But we now effectively control the destiny of all large, slow-breeding vertebrates. If the only places they can survive is in the parks we set up, and if we take a truly utilitarian and, dread word, holistic view of conservation, then we also have to take the responsibility of 'managing' their populations. Science isn't he only thing to guide us on such decisions, but it's best ot take as informed and clever a decision as possible, towards which Bode and Possingham's ideas can only help.

Thursday, February 08, 2007

Just Science day 4: Cursory

What's (even) more fun than blogging? Snow!

So, if you'll excuse me, I'm going to recommend that you check out this paper on potential pitfalls of digital photography in biology, and this article by the excellent Jenny Diski, providing a much-needed antidote to all the gush concerning Second Life.

And now I'm off to muck about on Hampstead Heath.

Wednesday, February 07, 2007

Just Science day 3: The H. pylori story

A new Nature paper by Mark Achtman and his colleagues reminds me that today, Helicobacter pylori (Hp) is definitely my favourite member of the human gut flora.

This bacterium is best known for causing ulcers and increasing the risk of stomach cancer. Barry Marshall and Robin Warren won a Nobel prize in 2005 for showing this (famously, few believed that bacteria could survive in the concentrated acid of the stomach, but Marshall chugged down a load of Hp, and got an ulcer.)

But the bacterium is much more than just a baddie. Once upon a time, it was probably in everybody's tummy (although no one is quite sure how its transmitted — vomit seems like the most likely culprit). It's still very common in developing countries and east Asia, but in Europe and North America it's steadily declined — only about 20% of US residents under 40 have it.

A good thing, you might think. But some scientists, such as Martin Blaser, have suggested that there might be a cost to this decline, as well as the benefit of reduced ulcers. Hp reduces the level of stomach acid, so without it there seems to be more heartburn, and possibly an increased risk of oesophageal cancer. There's also the general unknown consequences of having a part of the human ecosystem go extinct: "We have no good sense of the microbial ecology of humans," says infectious-disease specialist Julie Parsonnet of Stanford University in California. "H. pylori infection revs up the immune system - what happens to our ability to respond to other infectious agents when that isn't there?"

Another thing people have argued about is how the bug got into us in the first place:

Most mammals seem to have their own species of Helicobacter in their stomachs, leading some researchers to suggest that the relationship between microbe and host predates the evolution of modern humans. But others think that H. pylori's hook-up with humans, and subsequent spread around the world, was more recent.

That's the view taken by geneticist Douglas Berg of Washington University in St Louis, Missouri. Berg and his colleagues looked at more than 500 strains of the bacterium taken from people in five continents. Native Peruvians had bacteria more similar to Spaniards, they found, even though their genes are more similar to those of East Asians - the group that settled the Americas about 12,000 years ago. This led Berg and his colleagues to suggest that the conquistadors may have carried the bacterium to South America about 500 years ago, and that the continent's first humans arrived with virgin stomachs.

Martin Blaser disagrees. A microbiologist at New York University, he believes that Helicobacter has long been part of the gut flora of all humans. Late last year, Blaser and his colleagues seemed to reaffirm the ancient origins of American H. pylori, when they discovered strains closely related to the East Asian version of the bacterium in native people living in remote regions of Amazonia. And in unpublished work, pathologist Marvin Allison of the Medical College of Virginia in Richmond has detected H. pylori in the stomachs of 1,800-year-old Chilean mummies. In areas where Europeans and Amerindians had mixed, Blaser believes, indigenous strains have fallen victim to microbial imperialism.

The new study seems to confirm that Hp has an ancient origin. Achtman's team had previously shown that the spread of different Hp populations in stomachs around the world reflect the patterns of human migration. Now, they have found that we and them match up on a global scale:

[G]enetic diversity in H. pylori decreases with geographic distance from east Africa, the cradle of modern humans. We also observe similar clines of genetic isolation by distance (IBD) for both H. pylori and its human host at a worldwide scale.

So basically, we've been carrying it since we were human. Achtman has this graphic showing how the two spread:

Those of you with Nature subscriptions can read a 2003 feature by me on all this (which is where the earlier quotes came from). And if anyone's looking to write a short, sharp popsci book, you could worse than tell the H. pylori story. Just remember to give me a cut of the royalties.

Tuesday, February 06, 2007

Just Science day 2: They're only after one thing

Before we begin, I notice that the aggregator at Just Science has given yesterday's post the date of 31 December 1969. Can anyone help with why this has happened, and how to stop it happening again?

Anyway, on with the madness. With Valentine’s day just a week away, this paper in the new issue of Ethology is a must-read. In it, self-proclaimed ‘media friendly expert’, Karim Vahed, of the University of Derby, looks at nuptial gifts — the tasty morsels that many male animals (especially insects and spiders) bring to their intended mates.

The orthodox view of this is that everyone wins — the female gains a meal that increases her fertility, the male gets a mating. Vahed, however, has a rather more cynical take on things:

In this review, I explore the proposition that nuptial gifts act as sensory traps: by exploiting the female's gustatory responses, the male may be able to entice females to accept superfluous matings and/or transfer greater volumes of ejaculate than are in the female's reproductive interests.

Gift composition is more likely to be tailored to increasing the attractiveness of the gift to the female and/or maximizing gift handling time than to suit the female's nutritional needs … evidence suggests that the gift enables the male to overcome the resistance of the female to accepting an extra large ejaculate.

There is some evidence for this notion. Experiments in the fly Rhamphomyia sulcata suggest that females are almost as enthusiastic about worthless gifts as they are about a full dinner. Such indiscrimate behaviour leaves the door open to an invasion of cheating males.

And if Dr Vahed gives you a box of chocolates next Wednesday, beware.

Monday, February 05, 2007

Just Science day 1: cave bugs and shoot-em-ups

Not much time today (or tomorrow), so just a quick one drawing attention the juiciest morsels that popped into my inbox this morning.

First, and most closely related to this blog’s core themes, we have an interesting paper in Micobial Ecology by Raina Maier and her colleagues looking at the impact of tourists on the bacteria living in Kartchner Caverns, AZ.

These caves were opened to tourists in 1999. With admirable foresight (it’s depressing how rare this kind of thing is), researchers surveyed the caves’ microbial biota before opening, and now they reveal what’s changed as a consequence of having 200,000 people pass through the caves each year.

Raina's team found that the most heavily used areas had higher diversity, and different community composition — more Proteobacteria, fewer Firmicutes. This is probably a mixture of people bringing in bugs, and an increase in organic matter in the caves, say the researchers.

What we don’t know is what these changes mean for, say, nutrient cycling, food webs and so on in the caves, and whether they are something that should be of conservation concern. Microbial conservation is something I’d like to know more about, so if anyone has any pointers, please point them.

Three other things caught my eye:
1. Technological Forecasting and Social Change has a special issue of interesting-looking articles on terrorism and technology.

2. The Journal of Experimental Psychology reports that ‘action gaming enhances visuospatial attention throughout the visual field’ – i.e. playing Halo and its ilk makes you sharper-eyed. Whether this does you any good, and whether you get worse at anything else (insert your own joke about leaving the house, talking to girls etc.), is another matter.

3. And Psychopharmacology (always a favourite) finds that people who drink more coffee get more of a kick out of it. Which, given habituation and everything, seems to be the wrong way around. But I can’t tell from this abstract whether this is a consequence or cause of drinking lots and lots of lovely coffee.

There. That wasn't too bad. Back tomorrow.