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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Karl Popper

Karl Popper

According to Karl Popper, a respected 20th century philosopher famous among the scientific fraternity, true scientific theory makes predictions that can be empirically tested.

The superhero status of testable predictions has made good sense to me ever since I was exposed to it as an undergraduate back in the Carboniferous. Unless a theory can be tested it falls to the lowly status of opinion where only dubious predictions live; admittedly an overcrowded residence these days.

An idea, supposition or prediction attains the lofty moral position of a scientific theory a supposition or a system of ideas intended to explain something, especially one based on general principles independent of the thing to be explained — if it can be empirically tested, ideally through manipulations in controlled conditions with heaps of replication.

This much is grasped by most students of science, even the naive ones around when the trees were laid down for coal. It is the basics of the scientific method taught in every good high school.

Unfortunately, this is often as far as it goes. But there is more.

What Popper also realised was that scientists can never prove a theory to be true because the next test might contradict all that preceded it. Observations can only disprove a theory they cannot prove it. Empirical tests can only falsify.

This is way more subtle. Evidence from a controlled experiment might reject the hypothesis the experiment was designed to test but the alternative outcome (where evidence is not sufficient to reject the hypothesis) does not make the alternative (accepting the hypothesis) true. Empirical tests can only disprove, never prove.

Suppose I have a large field that I subdivide into twenty equally sized fields.

Into 10 of these small paddocks, chosen at random, I place five sheep for five days, remove them for 10 days and then put them back in. This rotational grazing goes on for a year. The other 10 paddocks contain no sheep at all.

The hypothesis is that grazing by sheep will decrease the amount of carbon in the soil. So before the sheep are introduced several soil samples are taken from all the small paddocks and tested for their carbon content. More soil samples are taken at the end of the year and their carbon content statistically compared with carbon content in the soil samples taken at the start.

It turns out that after a year the average carbon content from the grazed paddocks averages about 3%, slightly more than it was at the start, a small but statistically significant increase. In the paddocks without sheep, soil carbon also increased too but by no more than would be expected by chance (as determined by the statistical properties of the numbers generated from the soil carbon samples).

The hypothesis – sheep grazing will decrease the amount of soil carbon in the soil – is rejected given the empirical evidence.

The evidence is enough to reject the hypothesis and the temptation is to accept the theory that sheep actually do good things to soil carbon. Only Karl Popper would wriggle a little in his coffin if you made this call because should you do this experiment again, who knows what the outcome would be.

This example is phrased to follow the conventional wisdom. Current theory is that livestock grazing will reduce soil carbon over time as the animals metabolize the primary production and the farmer removes animals or their fleeces to market making for a net loss in soil carbon over ungrazed paddocks.

But if we rephrased the hypothesis as ‘grazing by sheep will increase the amount of carbon in the soil’ and the results of the experiment stay the same, then we accept the hypothesis. Again we are tempted to accept the theory that grazing by sheep is good for soil carbon levels only this time by claiming the results are a proof not a falsification.

Popper gets to wriggle again.

Interesting isn’t it. Even when science is done through determined experiments the outcome is not a given. Conclusions are also dependent on how the empirical test is conceived. This is why theory only gets such a lofty badge when there is repetition of empirical tests sufficient to reduce doubt but even then there is no proof, only falsification.

The sheep grazing example is naive of course and was phrased around hypothesis testing rather than theory. In reality, theory only achieves acceptance after many tests of many specific hypotheses. The process of iteration provides the rigor that allows scientists to rest easily at night without Popperian spectres messing with their dreams.

Only the example is also real.

We are not actually sure of the theory in this case despite the importance of grazing to food production and the reality that soils need as much carbon as possible to maintain that production.

Falsification is very difficult to do in environmental and ecological science, especially where soil is concerned. There is very little in the way of Popperian truth where fields, paddocks and remnant native vegetation is concerned. There have been way too few tests leaving fertile ground for opinion.

However, the risk in leaving issues of food security to opinion should scare the socks off you.