How to do science with the naivety of youth

How to do science with the naivety of youth

Image by Alloporus

Back when I was a bushy-tailed research student, life was a breeze that flew by without a thought. 

It was a time of naivety disguised as the fearlessness of youth. 

There were times I had to make some decisions but, fortunately, most were trivial and few animals were harmed in the making of them. In my case, this was a quirk of the University ethics committee. They decided that the invertebrates that were the subject of my experiments were not animals.

My research that I imagined was significant, attempted to build evidence for the importance of competition for food in the population biology of woodlice. Yes, staggeringly important information destined to change the world order and make a fortune for its finder. 

Well no, neither was ever the intent, for all that I wanted at the time was to stay at University for as long as possible. It was such a cool place. 

I justified this want by claiming to myself that my motivation was part progress up the academic ladder and part avoidance of the real world. And to this day, a stroll through any university campus easily confirms the prevalence of the latter. There is a heap of real world denial in the ivory towers.

But I digress.

The point here is that woodlice are animals and they are important decomposers. 

As they consume dead leaves and other detritus, they recycle organic matter and make nutrients available to plants. They are members of an army of organisms we cannot live without. 

Model woodlice 

In my research, woodlice were model organisms used to test the ecological theory of density-dependent competition. It is as nerdy as it sounds. 

The idea is that competition for food is one of the mechanisms for natural selection that ecologists have tried to prove ever since Darwin first put a name to it. The recycling credentials of woodlice and their soil animal cousins I studied later. At the time of my research degree, I needed a way to test if woodlice compete for food to add some more evidence in support of evolutionary and ecological theory. 

To do this, I had to make a decision on how to manipulate the availability of food on the assumption that it was a limiting resource. If the assumption was correct, theory suggested there would be competition for high-quality food and the woodlice would respond through changes in their patterns of growth and reproduction.

One manipulation option was to exclude (that is to keep out) rabbit grazing from an area of our study site. Rabbits! Where did they come from? Even the ethics dons would say these were animals. In the chalky grasslands of eastern England where woodlice are abundant, rabbits are crucial to the supply of high-quality food to detritivores, the woodlice. 

Rabbit grazing alters the structure of the grassland. The attention of many thousands of cute bunnies grazing on the grasses keeps the coarse grasses from taking over. Grazing opens enough light and space for forbs and herbs to flourish. Exclude rabbits, and tough grasses soon dominate in a thicker, dense layer. Dead herbs are the preferred high-quality food of woodlice so when the rabbits are first removed there is a spike in the availability of high quality detritus. A bonanza for the woodlice. Later when the thicker grasses took over  the herb and forb food source was reduced, so, in theory, the woodlice would become food limited and compete with each other.

So a rabbit-proof fence was constructed around part of the habitat and, sure enough, the grasses grew at the expense of the herbs and forbs sending through the pulse of high quality woodlouse food from the dead herbs and forbs. The area of rabbit exclusion became the Weeting Heath exclosure experiment. The driver we wanted to control was excluded.

Ecological research often works this way. In order to understand one species, you have to change things up with another, apparently unrelated species.

But this was only part of the evidence needed to test the density-dependence hypothesis of food limitation. I was keen to find out what would happen if we increased the numbers of woodlice in habitat with rabbits. The assumption here was that crowding them out would force them to compete for food.

In the second experimental option, rabbits would crop the grass and maintain the supply of herbs, but there would be an artificially high number of woodlice. Would that make these small critters compete for high-quality food?

This experiment is different. 

It required an increase in woodlouse numbers. Such manipulation is not easy to do over large areas. So I decided to create enclosures to keep high numbers of woodlice together with woodlouse proof fences. The fences had to be low enough to let the rabbits in to graze down the grass, high enough to stop the woodlice escaping, and surround an area big enough for the woodlice to behave normally, more or less.

The fenced-in areas became the Weeting Heath enclosure experiment. Here is what it looked like. The rabbit-proof fence of the ‘exclosure’ is in the background.

Keeping things out (the exclosure) and keeping things in (the enclosure) was an obvious solution to an experimental manipulation conundrum — two different ways to manipulate the supply of high-quality food for a wild population of woodlice.  

And just to be sure in some of the enclosures I added extra high-quality woodlouse food in the form of ground up leaf litter from alder trees. They love that stuff and grow exceptionally well on it.

Here you can see the darker colour of the grass in one of the enclosures where the extra food was added.

What happened?

Here are two of the conclusions we published in the Journal of Animal Ecology

(5) When an experimental exclosure was erected which prevented rabbit grazing, the availability of high-quality foods increased. Isopods within the exclosure grew larger, became more fecund, and consequently increased in density.

(6) In isopod enclosures to which high-quality food was added, growth rates of isopods also increased. In other enclosures to which sub-adult A. vulgare were experimentally added,  growth rates of  new recruits decreased. 

Hassall, M., & Dangerfield, J. M. (1990). Density-dependent processes in the population dynamics of Armadillidium vulgare (Isopoda: Oniscidae). The Journal of Animal Ecology, 941-958.

In less jargonese, the woodlice were bigger, reproduced more and their numbers increased in the exclosure without rabbits. 

Adding food in the enclosure also got the woodlice to grow faster but they grew more slowly when they were crowded.

Amazing, just the confirmation bias we were looking for and here is how we summed it up in the journal article

We conclude that intra-specific competition is important in regulating the density of this population and that populations of this macro-decomposer are more likely to be regulated from ‘below’ by competing for limited food than from ‘above’ by natural enemies. The relaxation of competition at low densities with the consequent positive effects on natality rates provides an effective ‘floor’ which-reduces the probability of population extinctions.

This is all a little grandiose. It initially seemed remarkably that these animals are sensitive to food supply but as every organism is the idea seems trite. Proof of sorts was worthy of a formal statement.

What I learned from exclosures and enclosures

Ecology is a messy subject with many challenges to the principles behind the scientific method. Experiments are never easy and here will always be criticism of most attempts.

My woodlouse attempts at experimentation were pseudo replicated, failed to measure controlling variables (food availability in the exclosure) and needed a much long run of observations. Just three obvious criticisms.

But I learned a great deal about these innate complexities and the difficulties of real world experiments. That was, after all, one of the reasons to take on a research degree.

I also learned that the theory holds. Organisms can be food limited with consequences for their survival, growth, and reproduction. Homo sapiens take note.  

Mostly though I found that scratching intellectual itches is great fun and immensely satisfying, so much so that I have kept doing it to this day and am unlikely to stop until my faculties do.

What a blessing it is to have an enquiring mind.


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Density and competition

Density and competition

In the second year of my PhD scholarship, I boarded my first aircraft, a bog-standard commercial flight from London to Rome but wow, what a thing?

The energy pushing you back into your seat, the stupidity of being suspended 30,000 feet up in the air and the impossibility of such a heavy tube of metal being able to get you and your seat up there. Just one experience I now take for granted that 30 odd years ago were a wonder to a youngster.

The journey was the first of many plane trips in my professional career, including some far more risky ones than a smooth jaunt across Europe. This first one was to attend a scientific conference, a meeting of minds for most of the world’s woodlice researchers. Some 50 people from all over Europe and North America who were into the behaviours, physiology and ecology of the terrestrial branch of Isopoda, an order of Crustaceans, the majority of whom live in water. The isopods that is.

So before we get to the publication, a brief ponder on the notion of a woodlouse conference. That humans, the most curious of beings, should have individuals dedicated enough to spend most of their waking hours understanding the biology of a peculiar group of animals that should be in the ocean but are not is quite miraculous. That these scientists can also be organised enough to get together periodically to discuss their obscure findings is bizarre too. This one in Urbino on the east coast of Italy in September 1986 was the Second International Symposium on the Biology of Terrestrial Isopods. It was a hoot, including a crustacean themed dinner with more than a dozen courses one of the very few meals from the distant past that I can still remember.

I was there to present some of my PhD research on competition and in the conference proceedings appeared my first single-author paper.

Dangerfield J.M. (1989) Competition and the effects of density on terrestrial isopods. Monitore Zoologico Italiano (N.S.) Monograph 4: 411-423

When reading this piece again for this post I could not even recall running the experiments the paper describes. It wasn’t until I read the methods of culturing broods of the tiny critters in plastic containers and feeding them uniformly ground leaf litter that it came back to me. The pots layered up on racks in controlled temperature rooms and hours weighing thousands of animals individually. Such is the dedication and forgetfulness required for higher learning.

A series of experiments tested the effects of crowding (although I called it density for formality) on growth, survival of young and the reproduction in adult Armadillidium vulgare, the common pillbug, with the general result that crowding matters. That is if you’re a woodlouse and you are around your woodlouse buddies too much they affect your biological success. The more is not the merrier for woodlice even if there is abundant food. Woodlice also compete against other woodlouse species, who doesn’t, only the win in the competition is affected by the size of the arena. It would seem that for woodlouse at least life is lived very much in three dimensions.

All up my conclusion and the most likely explanation was that there was interference going on in the cultures. The activity doing enough to generate measurable competitive effects. Noting that there was always enough food to go around, at least that is what I assumed. I remember being quite chuffed at this explanation because at the time the theory was that competition was not just about food but proving this was always tricky. So to have generated numbers suggesting it for such a lowly critter was fair play.

By Franco Folini – San Francisco, California, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=789616

It is hard to go past a simple experiment. Easy to design and deliver with all the satisfaction of hypothesis testing at the end. It’s the stuff of early career ecologists, they love it. I certainly did.

Did this science add to the pile of human knowledge? Well, not really, despite my enthusiasm over interference. It is likely that woodlice are competitive and these interactions can have consequences for their populations but there is also a lot more going on. Just because a mechanism exists does not mean it is important. But finding out that it is possible is worth the effort.

Later work could build on the findings but even in themselves, they show how complex patterns in nature can be. Today I would say that all of nature is constantly competitive. It is why we have natural selection and why there is so much diversity. Organisms become different to try and avoid as much of the constant competition as they can, usually with only limited success.

If nature is innately competitive, and we are of nature, not a rhetorical question, then we need not go much further than competition and how to avoid it as an explanation for many a human woe.

Back in 1986, that first plane trip got me started on my research career. My first single-author paper and a small but important step toward independence as a researcher.

Little did I realise how far and wide that journey would go.