Comment on In the Beat of a Heart

Hello. You've come here either through my regular blog page, or by following the 'comment' link at www.inthebeatofaheart.com. If you'd like to post a comment or observation on the book, bring my attention to some relevant research, or correct a mistake, I'd love to hear from you.

Book launch

On the off chance that anyone in on near Santa Fe, NM, reads this: I'll be talking about my book 'In the Beat of a Heart: Life, Energy, and the Unity of Nature' at Garcia Street Books next Saturday at 3.00 pm.

The Mike Leigh mark-recapture experiment

While standing on the platform of King's Cross Underground station last week (Metropolitan/Circle/Hammersmith and City lines, westbound, since you ask). I spotted Mike Leigh, director of, among others, the films Naked and Secrets and Lies. This is the third time in about four or five years that I have spotted him about the centre of town — I saw him once at an exhibition at the Royal Academy (I can't remember if it was Japanese prints or Renaissance illuminated manuscripts), and once walking down Charing Cross Road.

Now, every Londoner likes talking about famous people they have spotted in the street, pub or wherever (I saw Björk in a restaurant once, and sat opposite David Byrne on the tube). But this set me thinking about something different. How often can I expect to bump into a randomly chosen Londoner? Do I pass the same people every couple of years or so, but don't know it because they're not famous?

This is a problem that ecologists encounter all the time. Perfect knowledge of wild animals and plants is impossible, so we need techniques to estimate things such as population size, movement patterns, and mortality rates. One way to do this is a technique called mark-recapture. You catch say, 1,000 monarch butterflies, or cod, or swallows, mark them, and set them free again. Later, you see how many of the marked ones you can catch again, when, where, what percentage they make up of the recaptured population and so on.

This is used to estimate, among other things, fishing mortality, and was used to demonstrate the action of natural selection acting on the peppered moth: moths were much more likely to be recaptured in their camouflaged environment. Census takers, epidemiologists and others use similar techniques to estimate the true sizes of the populations they are interested in.

But answering my question raises lots of questions about sampling strategy. Who you see depends on where you go, and when. If one commutes into the centre of town most everyone is aged 20-50. If you want to see the elderly or children, you need to go out in the day. If I drove to work every day and spent the weekend playing video games, or doing DIY, my chances of spotting Mike Leigh would be smaller. Although most Londoners probably pass down Charing Cross Road every so often. how often they do so will depend on where they live, income and occupation. So, unless we all start behaving in a standardized way, we will all have different bumping-into frequencies for different (fuzzy) categories of people.

To answer my question, though, Mike Leigh seems like a good bumping-into benchmark, and an ideal subject for mark and recapture. He is random yet recognizable. I am not stalking him. I do not know where he lives, and, apart from being in central London, little connects the three locations in which I have spotted him. Apart from liking Japanese prints (or was it Renaissance illuminated manuscripts?) I would guess that we have little in common. If I were clever at maths I would use the parameters of my encounter rate, movement patterns and the population size of London to draw a curve plotting the probability of seeing him against time. But I'm afraid this is quite beyond me. So as it is, if you're reading this, Mr Leigh, I'll see you in 2008.

The British Ecological Society, and why ecology is unpopular

Last Tuesday (the 5th) I went to Oxford, to spend a day at the British Ecological Society's annual meeting.

A couple of things caught my attention: a talk (the 12.30 slot on this page) by Mairead Maclean of Exeter University, modelling the effect that domestic cats have on sparrow populations. If I remember this rightly, her study found that, in the area of rural Cornwall that she studied, a level of 80 cats per square kilometre would be enough to send the population into decline, whereas the actual level was 93. So it looks as if we might be able to convict cats of being one of the causes of the mysterious disappearing sparrows. She didn't think there was much cat owners could do about it — it seems to be a few cats doing most of the killing, with young and female cats being more avicidal than old and male cats.

The other thing, just 'cos it was related to the whole metabolic ecology, was a talk (the 16.00 slot) by David Coomes of Cambridge, looking at whether metabolic models can explain the size structure — how many big trees and small trees there are in a given area — of forests in New Zealand (this is also known as self-thinning). His conclusion (which was also reached by Muller-Landau et al., working on Sri Lankan forests) was that they can't.

This is not (as far I could tell — I may be misinterpreting here) because the view that metabolic rates influence population density is wrong, but because other things overlay the effects of metabolism, namely that old trees are more likely to die from getting blown over, disease etc., and young ones are more likely to die from being shaded out by big trees. This means that mortality is lowest for middle-sized trees (the graph of size against death risk is U-shaped), whereas (I think) metabolic models predict that mortality risk rises with increasing size.

But on the whole, I was surprised, looking at the meeting programme, by how little either grabbed me by the throat or seemed like it would make a good story, science-journalism wise. Nothing wrong with that, of course — the meeting's not set up for my benefit. But it got me thinking about why there is so little popsci on ecology. Here are some suggestions…

First, ecology is hard. Understanding the questions asked by people tackling say, the spatial and temporal patterns shown by forest tree species, or the influence that food-web structure has on ecosystem stability (to give two examples discussed at the BES), takes a bit of effort, but is not too hard.

Understanding the answers they come up with is a lot harder, particularly as the answers often seem to be uncertain, qualified and localized. Also, these ideas, as with most in ecology, do not have obvious parallels form everyday life, unlike, say animal behaviour, where the parallels between animals and humans are an ever-present reference point.

This complexity and unfamiliarity is also true of particle physics and cosmology, but people are probably more willing to wrestle with trying to understand the big bang, or quarks, because the ideas have more grandeur than, say, understanding the population dynamics of flour beetles. I enjoy quantum entanglement as a mind-blowing spectator sport, without really understanding what on it's all about.

Also, everyone asks her- or himself how the universe began, how the world will end, and so on, so such science taps into a pre-existing market. People love nature, but, I'd suggest, their relationship with it is less philosophical, more sensual and domestic. We marvel at the flowers in a meadow, but most of us don't ponder why the field contains that particular number of species.

Also, unlike animal behaviour, palaeontology or cosmology, ecology is not a narrative science — the work is hard to tell in the form of a story, cause and effect, and so on. One is asking why things are as they are, often trying to find an explanation that doesn't rely on history, rather than how they got that way.

And apart from conservation (in the widest sense, including fisheries, agriculture etc.), there are not many issues that seem to matter to people's everyday lives. And rather a lot of ecology — probably most — has nothing to do with conservation, it's folks trying to work out how the living world is put together. (Nothing wrong with that, of course, and nothing particularly unusual — most genetics isn't going to find a cure for cancer or inherited diseases, although geneticists are good at selling their research as if it might.) In fact, earlier this year the BES had to cancel a meeting on the links between ecology and sustainable development owing to lack of interest. Ouch.

This might come as a surprise, but then perhaps another problem is the very word 'ecology' which people tend to think is a Good Thing that is something to do with having a nice environment: pollution, energy generation etc. (The UK Green Party used to be called the Ecology Party, for goodness' sake. I don't believe density-dependent mortality was high on their list of concerns.) As far back as 1979, Stephen Jay Gould was lamenting (in an NYRB essay about Evelyn Hutchinson, I'm afraid I can't find the exact quote right now) that the word was so debased that its scientific sense had become meaningless to non-scientists.

So how to write about ecology? I've found that using people's stories and biographies can be a good springboard to writing about their ideas and work. I've also found that writing about the roots and origin of a question can lead one into writing about contemporary issues — particularly as most of the oldest questions in ecology are still unresolved. (This isn't such a revelatory solution, I know.) But this doesn't really help when one is sniffing round a conference for a 400-word news story.

How inordinately fond?

Reading a piece on Slate by Jordan Ellenberg about the proof of the Poincaré conjecture (something to do with the geometry of spheres), this caught my eye…

The entities we study in science fall into two categories: those which can be classified in a way a human can understand, and those which are unclassifiably wild. Numbers are in the first class—you would agree that although you cannot list all the whole numbers, you have a good sense of what numbers are out there….

In the second class are things like networks (in mathematical lingo, graphs) and beetles. There doesn't appear to be any nice, orderly structure on the set of all beetles, and we've got no way to predict what kinds of novel species will turn up. All we can do is observe some features that most beetles seem to share, most of the time. But there's no periodic table of beetles, and there probably couldn't be.

Mathematicians are much happier when a mathematical subject turns out to be of the first, more structured, type. We are much sadder when a subject turns out to be a variegated mass of beetles.

Nicely put. But beetles — and biodiversity — are not such a tangled, unknowable mass as you might think. For example, for trees there is a power-law relationship between number of species found in a place and the number of higher groups — genera and families (which are often seen as fairly arbitrary groups constructed for human convenience). Generally, there are also patterns in the relative diversity of different groups — crudely put, most higher groups contain only a few lower taxa (i.e. species), but a few are fantastically diverse. Beetles are one of these — they are often called a ‘hyperdiverse’ group (nematode worms have also been labeled such).

Hyperdiverse groups take up a large chunk of the diversity within their taxonomic level, and are found at all levels: so insects are a hyperdiverse group of animals, beetles are a hyperdiverse group of insects, and the chrysomelidae are a hyperdiverse group within the beetles. (There are also similar patterns in relative abundance — crudely put, most species are rare, a few are very common.)

Of course, describing a pattern isn’t the same as explaining it, and what’s still missing are theories (or at least, theories that most people agree on) that show why these patterns in nature are as they are, and whether they have to be like that. That’s one of the things that my book is about.