The Bill Effect


Entrance stone at Newgrange, Ireland. The upper opening is aligned such that once a year, at the winter solstice, the sun shines directly through and illuminates the interior. Picture by Ceoil and used under Creative Commons Attribution-ShareAlike 3.0 License.

As graduate students at the University of Leeds, there was a well-known phenomenon known as the Bill Effect. It could only be observed in a single location, the office of pollination ecologist Bill Kunin*. I experienced it on several occasions and it reverberates still.

Back then, for us, Bill was an intimidating person to talk to. Not because he was unfriendly; far from it, he’s one of the most genuinely warm and approachable people I’ve met in my career, and he always made time to help those students who needed him. His enthusiasm, encouragement and collegiate spirit have no doubt propelled many young scientists into successful careers**. Don’t get me wrong, Bill is great.

There was one minor barrier to a meeting with Bill, though largely practical and psychological. His office was opposite my lab, and therefore easily accessible, although he wasn’t my supervisor. But to meet him, you had to knock very loudly, then listen carefully for a response. I distinctly remember the view: an old fridge stood by the door, atop which sat a teetering mountain of stained mugs which had been used, set down and forgotten (the occasional Cleaning of the Mugs was a festival in the department calendar; suddenly the kitchen would be restocked with drinking vessels). Many a student with an appointment would knock timorously then hover outside in nervous apprehension. Bill, deep within, probably didn’t even hear them.

Two things set Bill apart. The first was that he spoke maths (or more correctly, being American, ‘math’). On our explaining some half-formed idea or incomplete hypothesis, his first instinct would be to formalise it as an equation. Now for young biologists this was a terrifying proposition. These simple functions appeared as arcane runes because our training in this regard had been so poor. In the UK it’s unusual for an undergraduate biology degree to contain much calculus, or indeed any maths beyond an applied approach to statistics. Likewise our post-graduate degrees lack any training element that would compensate for this. To cut a long story short, UK biology post-grads are in general pretty terrible at maths, and it’s not their fault.*** Talking to Bill meant confronting this insecurity.

The second was that Bill had a knack of asking the question beneath your question. This can be disconcerting to a postgraduate, who is usually interested in the answer to a single, practical issue, whatever is impeding their progress at that precise moment. Bill would seldom give you the straight answer that you desired; more often he would drill down and enquire as to what had brought you to this point. Being forced to describe and justify your underlying rationale can be alarming, especially if you’re not fully prepared for it.

This is when the Bill Effect would manifest itself. He would take the bare bones of your problem, weakly expressed as they were, and construct a logical argument before your eyes. As he declaimed his solution, hands whirling in enthusiasm, it was as though the heavenly spheres had aligned, and the bright light of understanding was shining directly upon you. Suddenly all was clear, suddenly it all made sense! It was exhilarating, and you left his office infected with his passion and positivism.

Sadly the Bill Effect was also fleeting; on leaving the office, within a few steps I had usually lost the thread of his argument, and by the time I sat down, it was entirely gone. Later I learnt to take notes but the first few times his insights simply evaporated before I was able to put them into practise. That simple discipline, however, of reverting to the fundamental basis of what I was trying to achieve, was always a worthwhile end in itself.

Why am I writing about this now, a good 15 years later? Well, I’m trying to think about how to be a more effective PhD supervisor to the post-graduates in my own group and those who consult me for advice. I don’t know what kind of PhD supervisor I am; I leave that for them to decide. Instead I’m thinking about the types of interaction with academics that left the most lasting impression on me over the years. Sometimes these were uncomfortable, intellectually challenging or emotionally draining, but they have stayed with me because they formed an essential part of my training, and have shaped my thinking for years thereafter. I would like to be able to recreate them for my own students; in this case by not just answering the simple question, but taking the time to understand a problem in its entirety and attempting to resolve it from the ground up.

If you’re a PhD student, there may be a member of staff in your department who fits the description above. They might even be your advisor or supervisor, in which case you’re very fortunate. My advice: seek them out. Expose yourself to thoughtful, critical, constructive scrutiny. It won’t be easy, and at first a lot of their insights might not stick, but in the long run it will make you a better scientist. Eventually you’ll realise that they’re having fun thinking about your problem, and that means so can you.


* Bill is still at Leeds — it would be interesting to hear from current post-grads whether he retains this particular power.

** He was so fired up after my talk at BES 2016 that he high-fived me, which I regard as an esteem indicator. I wish I could put it on my CV.

*** For this reason I prefer to take graduates in maths, physics or computer science as post-grads. I can teach a physicist how forests work, but it’s much harder to teach a biology student how to set up a directed percolation model.


Confessions of a former creationist


Still from Rise of the Planet of the Apes (2011).

I used to be a creationist. I have no qualms about admitting this now, despite being an established academic ecologist. I teach evolution at university, have written a textbook in which evolution is simply an accepted fact, and have donated to campaigns to teach evolution to schoolchildren. I’m not ashamed of my past, partly because there’s no point, but mostly because I still remember how creationism fit into a wider pattern of beliefs and attitudes that I once held. Evolution is scientifically, factually, demonstrably true. But at the time, for me, divine creation was The Truth.

This post is an attempt to explain how my background allows me to remain sympathetic towards creationists, and to help others from more secular or scientific backgrounds to understand how a creationist worldview can persist despite such overwhelming and widely-available evidence to the contrary.

I grew up in a fundamentalist Christian church. Which one is immaterial — there are many similar religious groups across the world, and they are not exclusive to Christianity. What they share is a collective desire to inculcate the children of their members in a specific set of beliefs. Mine was regressive in many ways; women had to wear hats in the church and were excluded from any formal roles. It has taken many years to realise how these features of my upbringing, which I accepted as normal practice, shaped attitudes in my later life that I have fought hard to correct. Perhaps this can be a subject for a future post. But one clear message, delivered from lay preachers at the pulpit, from Sunday School teachers, from the in-house literature laid out for our edification, was that evolution was a lie.*

The vehemence with which evolution was rejected was derived from a foundational belief in absolute Biblical truth. This didn’t quite go so far as a strictly literal interpretation: not all members of the church thought that creation took place in six days, and the extreme positions of Young Earth creationism were rarely advanced. But the Genesis account contained several features that were inconsistent with evolutionary theory, particularly in the order of appearance of different life-forms, or the idea that all species were created simultaneously. Most importantly, it conflicted with the separate creation of Adam as the first human, and of Eve as being formed from his flesh.** From an early age it was drilled into me that the Bible was the first authority, and evidence that did not fit was inherently suspect.

I recall being startled that so many people were willing to swallow the lie that was evolution. This genuinely perplexed me; what was in it for them? I don’t recall any cognitive dissonance over the overwhelming evidence in favour of evolution, mainly because I didn’t hear it, or look for it, and most likely would have ignored it anyway. One evening that has lived long in my memory was when our church held a ‘debate’ about evolution. In the absence of anyone willing to make a case for evolution, my father and I were enlisted to act as Devil’s advocates. That we were entirely unable to muster a coherent argument illustrates the depth of our ignorance at the time.***

Another feature of our church, and indeed of many non-conformist sects, was a confrontational approach to debate. We were trained in this, even taught to expect it when defending our beliefs. Differences of opinion within in the church were usually resolved by the open setting out of arguments and persuasion, rather than by respectful listening and thoughtful contemplation. In argument I am a belligerent opponent, not averse to deploying a battery of dirty rhetorical tricks to sway an audience. On the other hand, once persuaded of a case, I can be a strident ally. I know full well that this is not one of my most endearing personality traits.

What this meant was that the concept of being set against the world and its lies was impressed upon us at an early age. It was almost a heroic mission. At school as a late teenager I thought nothing of confronting my teacher when evolution was considered, turning one particular class into a fractious dispute. Who knows what the rest of the class thought; they were kind enough not to tell me.**** To my teenage mind, I was simply standing up for my beliefs, and being a lone voice only increased the responsibility I felt to hold my ground.

At the time the school syllabus in the UK contained very little evolution; it may be central to biology but the majority of the content was narrowly factual. It was entirely possible to get through school with straight-As in science while denying evolution entirely. I know because I did. Right up until I arrived at the University of Cambridge to study a degree in Natural Sciences. I reached the pinnacle of academic achievement within the UK educational system, and walked into the gates of Trinity College at the age of 18 still an ardent creationist.

My Damascene conversion came quickly, but it was not caused by losing an argument with a more experienced opponent, hearing a case against creationism, or even for that matter encountering one in favour of evolution. It came as I was exposed to a semester of lectures and laboratory practicals on invertebrate anatomy and physiology by Richard Barnes (our textbook was the magnificent Barnes et al.). He methodically outlined the structures of organisms, their development and the linkages among them. I don’t recall him ever even mentioning that this was magnificent evidence for evolution over creationism. He didn’t need to: it was obvious.

Halfway through the semester I got into another argument, only this time the tables had turned. In the church I was attending in Cambridge, I tackled a speaker on the subject of evolution, armed with only a few weeks of first-year undergraduate knowledge. I was a lone voice. This did not dissuade me. Looking back what is most striking is that, within 12 months, I had entirely switched corners, but was still quite willing to take on the whole room against established authority. Plus ca change…

That argument was particularly vitriolic, and led to me leaving the congregation. For some time afterwards, members of the church would track me down to explain the errors of my ways, but I never went back. It started a three-year journey that led, eventually, to my leaving religion altogether and becoming a firm atheist. It is a position I have held, against the views of most of my family and childhood friends, for nearly 20 years. I believe in humanism now as strongly as I ever believed in Christianity, and I will stand toe-to-toe with anyone on the topic. But my arguments are more securely formed for having the experience of once taken the other side and been entirely committed to it. I have fought with myself and, while one side won, I can still hear the other.

Here is where I think many fellow scientists, sceptics and rationalists can learn a trick, because there are many who simply find the creationist perspective as incomprehensible as I once found theirs. If you were raised in a secular household then you may never have met the arguments raised against evolution, and treat those who hold them as ignorant dinosaurs. If your knowledge of evolution is based solely on the high-school syllabus and received truth from scientific authority figures then, quite frankly, you’re not fully equipped to enter a debate on the subject with a well-prepared adversary.

To conclude, here are some lessons from my experience which may help in thinking about tackling entrenched, anti-scientific attitudes such as creationism.

Don’t bother getting into an argument with a committed creationist. Someone who holds creationist views based on their religion will not back down, even when outnumbered and in a corner. They have been trained to expect this. Ridicule, exasperation and insult are never effective tactics for persuasion, but actually the debate in itself usually won’t be sufficient either (for your opponent at least, although you can still win over an audience). A calm presentation of evidence is usually more effective. It is unlikely that they have ever been exposed to the facts supporting your case. Suggest to them that, in order to better understand what they’re objecting to, they should read one of the many introductions to evolutionary biology, then invite them to come back and discuss it at a later date. Out of politeness you might agree to do the same (and you can probably guess which it will be).

If you teach biology in Higher Education then you have creationist students. This is a simple statement of fact. In my twelve years of teaching at the University of Nottingham I’ve known of several; many more have no doubt kept their heads down. Insulting creationists for cheap laughs in lectures is unlikely to do anything to persuade them (sadly I haven’t been above this myself); more likely they will stop coming to your lectures. I would advocate not even mentioning creationism at all. Let evolution permeate your teaching, and eventually it will filter through to any thoughtful student.

Most of all, don’t look down on creationists. They are not ignorant, nor stupid, although they may be misinformed (wilfully or otherwise). They are often highly intelligent people whose opinions are internally consistent, and whose arguments are coherent, but derived from a different set of authorities to your own. Evolution is often rejected because it is perceived as a challenge to this framework, even if not a fundamental element. You will achieve more by finding ways to make evolution fit within their existing mindset than attempting to bring the whole structure down.***** Realising that evolution is true is revelatory and inspiring, but to accept this, your listener has to be convinced that it isn’t a threat. Otherwise you will only encounter an aggressive defence.


* One visiting speaker to our youth group made the case that dinosaur bones had been placed in the earth to give a 6000-year-old Earth an illusion of history; in other words, God had placed them there to test and deceive us. He got short shrift from many of us, but the point is that he was invited in the first place. It’s an old lie, but somewhere in your local town, I’m prepared to bet that children are still hearing it to this day.

** It is ironic that misrepresentations of scientific evidence, such as ‘mitochondrial Eve’ or ‘Adam’s Y chromosome’, have in recent years become an established part of attempts to defend the biblical account. Creationists are not averse to adopting the language of science when it fits their overall narrative.

*** To his credit, and partly as a result of taking an interest in both science in general and what his children do do, my father has since changed his mind.

**** A factor in this was that there were two biology teachers at our school, and one of them was a creationist. During my final few years he was away for long periods, but he had a continuing influence on me. On the one hand, I can genuinely thank him for inspiring me to study biology. Nevertheless, even in his absence, he gave me confidence that there was a scientific case for creationism.

***** There are of course many religious scientists who have no problem with evolutionary theory. I have several colleagues who are committed Christians, and suffer no cognitive dissonance as a result, despite the assumption by many hardline sceptics that they should. In this I would only note that we all hold internally contradictory positions on a range of topics; perhaps your weak spot is in politics or educational theory. I’m sure that I have plenty.

How to avoid the Allee effect, assuming that you’re a tree. Or a barnacle.

The Allee effect is familiar to anyone working in conservation, often colloquially described as the phenomenon whereby at low densities, populations become more vulnerable to extinction. This contradicts one of the assumptions of basic population models, which is that when competition for resources is low, populations should grow quickly. Instead this advantage is overcome by other factors, such as the difficulty in finding mates, or in resisting predation.*

More strictly, Allee effects are defined as positive density dependence in populations, that is to say, where increasing population density actually increases the fitness of individuals. When Allee effects are strong, they can result in populations shrinking in size when they’re below a critical level known as the Allee threshold. Above this point, the population will grow until eventually competition takes over and it reaches its carrying capacity (the equilibrium at which births and deaths are exactly in balance). Below the Allee threshold, the population shrinks and will inevitably go extinct. In conservation this is a bad thing, but if you’re trying to control an invasive species or a crop pest then it can be very helpful. Allee effects are therefore extremely important in applied ecology.


The growth rate of populations varies with their density. At high densities competition for resources causes the population to settle on a stable equilibrium known as the carrying capacity. At low densities the population slips beneath the Allee threshold and starts shrinking.

That’s how it works in theory. But in my research over the last few years, working with Jorge Velazquez, we’ve been examining how these simple population models respond when you take into account the spatial patterning of populations. Most individual organisms are not distributed regularly across habitats. Instead, they are often clustered, which means that from the perspective of an individual, the actual population density it experiences is higher than the average for the habitat as a whole. If individuals are spread out (perhaps in territories) then the opposite will be true.

This becomes important because species vary in the range over which they can do important things such as mate or disperse their offspring. A tree such as silver fir is wind-pollinated, and therefore effectively unlimited in the distance over which it can mate with other trees. Its seeds, however, are large and don’t travel anywhere near as far. In other words, it mates over longer distances than it disperses. Other trees, such as dipterocarps, are pollinated by insects which are unable to fly very far, and also have massive fruits that mostly fall right next to their parents. They are limited in both mating and dispersal.

Jorge and I had the idea that this difference in the ranges over which individuals could mate or disperse might affect their vulnerability to Allee effects. The missing element, however, was finding a species that could disperse over long distances but only mated over a short range. I couldn’t think of a tree with those characteristics**, but another organism I’ve worked on was ideal — barnacles!


In our new paper in Ecological Modelling we show that this variation in relative ranges of mating and dispersal changes the behaviour of whole populations, and makes some species more sensitive to Allee effects than others. We first show the principle mathematically, then demonstrate it using models for each of the three species above.

Fir trees don’t have any particular problems at low densities, although once populations build up they compete strongly for space because they can’t disperse their offspring very far. Dipterocarps, on the other hand, benefit from being clustered, because this makes it more likely that they will be able to find a mate.*** Their Allee threshold goes down; in other words, they are more tolerant of low population densities, and even of high mortality rates, as might occur if there is harvesting of trees. This benefit occurs despite competition for space within clusters.

Barnacles are an odd case because, although they don’t move during their adult life, their larvae are widely dispersed in the water. Nevertheless, barnacle larvae don’t just wash up on rocks randomly. They decide which areas to settle in, and once they find a suitable location, they move to be closer to other barnacles. In other words, barnacles deliberately cluster. This gives them the best of both worlds: they can escape competition from their parents, but benefit from the physical proximity required to reproduce. Their Allee threshold drops even further and their populations are highly resilient.

Measuring the ranges over which species can mate or disperse can have important implications in conservation and applied ecology. It’s not just a matter of having more accurate models; these principles could be used to identify species with particular combinations of traits which cause them to be vulnerable to Allee effects, and thereby make conservation of rare species more effective. Our models show that when finding a mate is the greatest challenge faced by an organism, increasing their clustering boosts the resilience and persistence of their populations. This trick might turn out to be very useful.

Velazquez-Castro J & Eichhorn MP (2017). Relative ranges of mating and dispersal modulate Allee thresholds in sessile species. Ecological Modelling 359, 269–275.

* It’s sometimes said that random fluctuations in small populations (e.g. in sex ratio) that increase their probabilities of extinction are Allee effects. I don’t agree that demographic stochasticity should be included because it doesn’t alter individual fitness.

** Please let me know if you can! Perhaps there’s a species with tiny pollinators but which is animal-dispersed. My expectation is that this should be a very rare combination of traits because their populations would be very unstable, and I’d be interested to see if any species can manage it.

*** If you’re wondering whether this might cause inbreeding, then that’s a reasonable question, but the answer isn’t straightforward. There is some evidence that species with poor pollen dispersal are more tolerant of inbreeding, which would reduce the apparent costs. There might be a complex evolutionary relationship between dispersal mode and inbreeding tolerance which is something to consider another time.

Unsavoury scientific pasts

This weekend I wrote an article for the BES Bulletin in which I referred to an intriguing character, Otto Schultz-Kampfhenkel (1910–1989). He was a German geographer, explorer and film-maker, whose lasting legacy was to have founded an institute producing educational films for schools on global matters (it still does). He also established a field centre in Portugal where I’ve taught and carried out some research, which is how his name first came to my attention.

Schultz-Kampfhenkel was well-known for his 1933 book Das Dschungel rief (The Jungle Cried), based on his expedition to Liberia, and a film Rätsel der Urwaldhölle (Riddle of the Jungle) from his 1937–37 expedition on the Amazon. Both are very much products of their time and, while no doubt valuable for their anthropological records and natural history observations, they are likely to be uncomfortable for modern audiences. One of the main reasons for this is that Schultz-Kampfhenkel was a Nazi.


A photo from the 1935–37 expedition on the Brazilian Amazon. I can find no evidence that Schultz-Kampfhenkel appears in this image; only that this was the team which he led, and clearly the flag that they carried.

Examining the careers of European cultural, academic and scientific figures of the mid-20th century always carries some trepidation. Many made compromises in order to protect themselves or their families; others found ways to manipulate the system to advance their own interests, regardless of their own personal affinities. My own family history contains examples, and it’s important to not make too many moral judgements from a distance that is now not only historical but also social and cultural. We cannot know how we would have acted in such circumstances; go back far enough and all of us are descended from murderers.

Such equivocation is unnecessary with Schultz-Kampfhenkel, who by all accounts appears to have been an enthusiastic fascist and collaborator with the wartime regime. One of his core activities was to set up a group of scientists to advise the German war effort. This included geologists, geographers, environmental scientists, foresters and, to my surprise, a botanist: Heinz Ellenberg (1913–1997), one the foremost vegetation ecologists of the mid-20th century. His works on the formation and classification of plant communities remain some of the most important contributions in the history of the field. Together they produced military maps for assessment of terrain and landscapes, based on both aerial photography and field surveys.

We of course know more of Ellenberg from his later career; after the war he worked with  Heinrich Walter in Stuttgart-Hohenheim*, and was later appointed as director of the Geobotanical Institute at ETH Zurich where he led the conceptual development of UNESCO’s Man and the Biosphere (MAB) programme, one of the most transformative innovations in conservation policy. To my mind, however, Ellenberg’s greatest contribution was the book Vegetation Mitteleuropas mit den Alpen in ökologischer, dynamischer und historischer Sicht (first edition 1963, with the last produced by Ellenberg himself in 1996). This has sat on my bookshelf (in translation) for 20 years now, and I still periodically refer to it as a trove of observations, measurements and insights. There is so much data in there that would be unpublishable in the modern world, even unthinkable that someone would bother to collect it (or to fund efforts to do so), and yet, as time goes on, this record of the vegetation of Europe in the 20th century becomes ever more valuable.

Why does Ellenberg’s name on the list of distinguished academic contributors to the German war effort matter? Perhaps it shouldn’t. Scientific facts are not in themselves political, even if scientists themselves are, as is often their funding, as well as the uses to which their work is put. Stripped of its political motivations, we can still learn from studies arising from even the most distasteful of sources. More to the point, Ellenberg’s most important academic contributions all came long after the war. I know a number of emeritus vegetation ecologists in Germany and the UK who must have met Ellenberg in person. Some of them even worked with him. Perhaps my discovery would not be news to them; they could even provide some clarificatory context to assuage my discomfort. Or, as with many of that generation, maybe it never came up in conversation.

Perhaps I shouldn’t be shocked to find this skeleton in Ellenberg’s closet, although what surprises me more is not that a man of his age was involved in the war effort, but rather that it was in his capacity as plant ecologist. I have my own strong political opinions as a socialist and committed anti-fascist. I’d like to think that none of this inflects my work (at least not in content, although whether it does in conduct is a different matter). Nor would I expect anyone reading my work to judge its value through that prism. Nevertheless, were there some way in which I could use my expertise to advance the causes I believe in, I would have no hesitation**.  None of us are only scientists. Was the same true of Ellenberg?

Learning the about the histories of influential scientists can have mixed results. Some have risen in my estimation as I’ve discovered more about their exploits (like the legendary botanist Richard Evan Schultes); others I can continue to admire while not wishing to spend any time in their company (see the recent Robert Trivers autobiography), while some turn out to have been surprisingly boring. We care about them as people because we are social creatures (mostly), but this should have no bearing on our estimation of their contributions to science. Nevertheless, however hard I try to rationalise it away, finding Ellenberg’s name on such a list has left a bad taste in my mouth. One of the giants of the field just became, for me, much shorter.

* Walter’s foundational work from the 1970s Die Vegetation der Erde in Öko-physiologischer Betrachtung was still core reading when I was an undergraduate in the 90s, and remains in print in the form of Breckle’s much-updated edition.

** I don’t see right now how my work on forest structural organisation is going to lead to a radical rebalancing of the social contract between our government its people, but if you can see a way then let me know, and quickly — we have an election coming up.

How much stuff is in a forest?

Forest are complex, messy habitats. The tired old saw of not being able to see the wood for the trees has an element of truth, because the tangle of material prevents easy measurement and assessment. And that’s without even mentioning the leaves.

Terrestrial laser scanning (also known as ground-based LiDAR) is a great technology for getting round this because it allows us to create full three-dimensional reconstructions of forests, from which we can extract parameters that would be otherwise unavailable to a surveyor on the ground. In this aspect it’s a major advance over traditional techniques of forest surveying, though challenges remain in turning the vast quantities of data into relevant and meaningful measurements that we can use to understand how forests form and what the implications are.


One of our laser scanners in action in a UK woodland. Photo by Joe Ryding. If FARO want to give us a discount for all this free advertising then I’d be very happy to hear from them.

In this post I’d like to focus on some of the findings of our recent paper in Journal of Applied Ecology that might have been overlooked in the media hullabaloo. For a reminder of the major findings, and what I think the implications are for forest conservation, see my earlier post. In any paper, however, there are always some hidden insights that couldn’t be elaborated on in the space available.

In this post I’d like to ask: how much stuff does a forest actually contain? In answering this, our data is perhaps non-intuitive. We split the whole forest into 1 cm cubes then asked whether each contained wood, leaf or neither. Terrestrial laser scanning can’t see inside stems, so instead we measured the surface area of trunks and branches*. Rather than using LiDAR to simply recreate the metrics we can obtain by other techniques, I think the future will be in learning to use these outputs more directly as indices in their own right.


Vertical distribution of foliage in 40 UK woodlands, split into those with either high or low deer densities, and which were either managed or unmanaged.**

Our scans found that woodland plots contained an average (median) density of leaves of 523 cm3/m3. What that means in real terms is only 0.052% of the total forest volume. In other words, although a forest looks like it’s full of foliage, actually it’s mostly empty space. This is necessarily a minimum estimate because we probably failed to detect many leaves higher in the canopy because our laser beams were blocked by other material getting in the way. Even so, if we only detected half of all the foliage in the forest, it would still be less than a tenth of one percent of the total volume.***

If forests are mostly empty space, this has a number of interesting implications, one of which is for the movement of species. For large, lumbering mammals like ourselves, we perceive forests to be difficult to move through, but for small insects they contain vast distances which need to be traversed. Organisms that can fly find this easier, others will depend on physical linkages to help them move around. The amount of stuff in a forest, along with its density and distribution, will have major influences on the mobility of organisms of all sizes.

Another implication is that we can treat the three-dimensional surfaces of forests as area in much the same way as in less complex habitats. This is actually an old idea, with Southwood coining the term ecospace to describe the effective area presented by a habitat, and proposing that this increased area might be responsible for differences in diversity between habitats. For the first time we have a straightforward way to measure the amount of leaf in the forest, which is a metric of how much habitat space there is for the many organisms that feed on or move across them. We could potentially compare this between sites.

We can do the same thing with stems, remembering that our measure is of surface area rather than woody volume. The area of stems in these woodlands was an order of magnitude lower than of foliage, at 49 cm3/m3. This is interesting because it tells us that for species that forage on tree trunks and branches, there is approximately ten times less area available to them than there is for those utilising leaves as habitat.

The Species-Area Relationship (the closest thing ecology has to a law) tells us that the number of species doesn’t increase linearly with area****. Instead, we would expect a 90% reduction in area to mean a roughly 50% reduction in species richness. Is that true? Do we find half as many species of insects, lichens or gleaning birds on bark as we do on leaves? I’d be interested to look. Unfortunately right now we don’t have an easy way to tell live and dead wood apart, which is important because they form habitats for completely different species.

In short, capturing the three-dimensional structure of these forests is just the beginning, and there are all sorts of new avenues which we can explore with these data.

* A range of algorithms exist to convert these into volumes using cylinder fitting, which is the standard approach used if you want to determine either the amount of timber or carbon in a forest. These weren’t part of our objectives so we didn’t, and actually as a measure of habitat structure as experienced by other organisms, surface area might be more relevant.

** Note that these figures are flipped relative to those in the original paper. This is a more intuitive way of looking at the patterns, whereas in the paper the orientation was set to match the statistical analyses.

*** Strictly this is ‘number of 1 cm cubes per cubic metre which contain foliage’. Leaves are flat and much thinner than 1 cm, of course, so the true volume of foliage is much, much lower than this.

**** The actual relationship is S = cAz, where z is a parameter determining the sensitivity of species richness S to area A, and c is a mathematical constant representing the theoretical richness of a single unit of area.

Should we eat Bambi?



Fallow deer in Avon Valley Country Park, Bristol, UK. By Adrian Pingstone (Own work) [Public domain], via Wikimedia Commons. Note that deer kept in parks are not part of the problem; this just happens to be a nice picture of them. Leave these deer alone.

 Our new paper has just come out in Journal of Applied Ecology, in which we’ve used terrestrial laser scanning to examine the three-dimensional structure of 40 lowland British woodlands. We compared woodlands in areas with high and low deer densities, and which were either managed or unmanaged. One of the main findings will surprise no-one: in areas with lots of deer, there is much less foliage at heights below 2 m. What makes our study unique is that we were able to quantify this as a 68% reduction. The interesting results don’t stop there though; there were other differences between high- and low-deer woodlands, extending right the way through the canopy. High-deer woods were on average 5 m taller for some as-yet-unknown reason.

In another post on the Journal of Applied Ecology blog I’ve described these findings in more detail and explained their specific implications for forest management. Here I’m going to use my own site to step over the line into more controversial territory and ask what this means for the broader issue of conservation policy. Note that these are my personal opinions, and go some way beyond what was said in the paper itself*.

First, there are vast numbers of deer in the UK. Their populations have boomed over the last century for a number of reasons. These include a lack of natural predators (wolves and lynx disappeared centuries ago) along with a range of other factors that might include an increase in woodland area, planting of over-wintering crops, and perhaps also impacts of milder winters on their survival. The UK is not alone in this; similar patterns have been observed elsewhere in Europe, throughout North America, and in Japan.

One of the features of the deer we find in British woodlands is that they are overwhelmingly made up of non-native, invasive species. In our study most (85%) were fallow deer, pictured above, which were introduced in the 11th century for sport hunting in deer parks. They are joined by Reeves’ muntjac, a small Asiatic species that probably escaped into the wild in the 19th century. It’s worth emphasising that I bear no grudges against the large, noble red deer of Scotland, nor the scarcer native roe deer, which we seldom detected in our surveys.

Our work has shown that in areas with high deer populations (more than 10 per square kilometre and often much higher) there is a loss of complex understorey vegetation. This dense ground-level foliage includes the regrowing seedlings and saplings of canopy trees, as well as providing habitat for a wide range of birds, small mammals and insects. That many woodland birds have been in decline over the last century is probably not coincidental, and consistent with patterns seen elsewhere in the world.

There are several options to keep deer out of woodlands, but most are either infeasible or ineffective. Fencing is an option, but it’s enormously expensive to establish and to maintain. Moreover, the longer a woodland is left without deer, the greater the amount of palatable foliage that will build up, and hence an ever-increasing incentive for deer to find their way in. It’s also difficult to keep small deer out while allowing passage to the other animals we would wish to have free movement around the countryside. For this reason fencing can only ever be a local and temporary option. Deterrents are also unlikely to be effective. Chemicals soon wash away, and deer quickly learn to ignore attempts to scare them. These tricks might work briefly but they won’t keep deer away for decades, which is what we need to do if we would like complex forest structures to develop.

What then can we do? Let’s tackle that thorny euphemism, ‘control’. What this almost invariably means is finding a way to reduce deer populations. In such circumstances  well-meaning people will always suggest sterilisation, although this would be prohibitively expensive to apply to many thousands of deer, and probably as stressful as any other action. The next option then is that most unpopular of conservation moves, a cull. These are still expensive to carry out and to maintain over long time periods, at least in open landscapes where deer can constantly wander in from elsewhere. What do we have left?


Venison escalope in Switzerland. By Kueued (Own work) CC BY-SA 4.0-3.0-2.5-2.0-1.0, via Wikimedia Commons. Serving suggestion only.

We can eat them. It’s almost the same as a cull, except the meat doesn’t go to waste, and the market would help fund deer control. Fallow deer were actually introduced to the UK by the Romans a thousand years before the Normans brought them here, but died out — probably because they were eaten. Together we can do it again.

Venison was a traditional meat eaten throughout the UK only a century ago, as it remains in many parts of Europe. If wild-caught, free-range British venison were to appear in our butchers, on supermarket shelves and restaurant menus, we would only be restoring it to its former popularity**.  Another benefit is that it would provide a source of income for rural communities, many of which are among the most deprived in the UK. The same approach could be taken with wild boar, though my suspicion is that this would not be as effective at controlling their populations***.

Will this work? Nothing in ecology (or life) can ever be guaranteed. When we intervene in complex systems there is always the chance — indeed the likelihood — of unforeseen consequences. The only way to guard against this is through careful monitoring and intervention. If the aim is to restore forest structures then we don’t yet know how low deer populations need to be brought down, over what time periods, and whether market forces will be successful in achieving this. What we do know for certain is the effect of doing nothing. If there’s a chance that eating deer might work then, if you’ll pardon the pun, it’s worth a shot. And venison is delicious.

Eichhorn M.P. , Ryding J., Smith M.J, Gill R.M.A , Siriwardena G.M. and Fuller R.J. (2016). Effects of deer on woodland structure revealed through terrestrial laser scanning. Journal of Applied Ecology, in press. DOI 10.1111/1365-2664.12902

* One of the reasons I’m writing this here, rather than in the paper itself or the journal blog, is that the authors of the original paper wouldn’t all necessarily agree with my prescription.

** In North America hunting is a popular rural pastime and, contrary to the perception of outsiders, has little to do with taking down large animals for display. The majority of people hunt for the table. Why then has this not led to effective control of deer populations? This is probably down to two factors. The first is the vast area of North America, much of which is wooded, and with low densities of people. The second is that game laws regulate hunting so as to maintain populations of deer (at least in part) rather than for the conservation benefits.

*** What we refer to as wild boar in the UK are actually a breed of pig. Although they have escaped and naturalised (and trash habitats in places like the Forest of Dean), when you buy wild boar sausages in the shops it doesn’t necessarily imply wild-caught boar. Most meat still comes from farms. The reason I don’t think we will control wild boar by hunting alone is that they breed at an incredibly fast rate, whereas deer populations grow much more slowly.

What academic journals should I follow?


Yay, more journal issues have arrived! I’ll add them to the heap. It’s becoming a fire hazard.

A few years ago I bemoaned the fact that I had effectively stopped reading the academic literature. Despite apparently being a common phenomenon among mid-career academics, at least based on my conversations with colleagues, it provoked a nagging guilt. How can we tell our students to read constantly if we don’t practice what we preach?

Over the years the table of contents emails continued to pile up, causing permanent low-level stress as I realised how much interesting, relevant and important science was simply passing me by. But there was no time to do anything about it, nor would there ever be. With a heavy heart I deleted them all. This has, in effect, blinded me to several years of output in almost all of the journals that I used to follow*.

That’s not to say I haven’t been reading any papers. Every time I need to write a manuscript, proposal or lecture, I’ve carried out a targeted search and found what I needed to get the job done. This is a limited way to learn about science though; it doesn’t expose you to as many new ideas. I was raiding the literature, not reading it.

I’ve now come up with a new system based on the principle that it’s better to do a small amount well than attempt too much and fail. This involves selecting ten journals for which my aim is to scan the contents for every issue, and read the papers that are most compelling. They make up my ‘essential’ list. Next are a set of ten for which I will scan them if I have time, but if the next issue comes out before I’ve had a chance, they’ll be ignored. This means I will only follow a maximum of 20 journals at any given time**.

Essential: Science, Nature, PNAS, PRSB, Nature Ecology & Evolution, Ecology Letters, Ecology, Journal of Ecology, Ecological Monographs, TREE.

Time-permitting: American Naturalist, Nature Communications, Methods in Ecology & Evolution, Frontiers in Ecology and the Environment, PPEES, Forest Ecology and Management, J Veg Sci, Biotropica, GEBJournal of Biogeography.

I could easily list another ten, or twenty, that I would love to read if there were room in my life, but there isn’t. It’s been a tough decision-making process. If you’ve tried something similar, then what did you end up with? How did you decide? If anyone is interested then my rationale for selection is below the fold.

I’ve focussed here on how to keep pace with new literature. It doesn’t even mention other issues such as the value of reading older papers, reading outside your own narrow field of study, or whether sometimes it’s best not to read at all. Some people will even argue that the whole concept of journals is becoming obselete, and in a world of online search engines we no longer need them as anything other than gatekeepers. I have some sympathy for this view, but the Brave New World has yet to arrive, so I’m making use of the system we have.

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