The Editor’s Choice for the next issue of Journal of Ecology is “An ideal free distribution explains the root production of plants that do not engage in a tragedy of the commons game” by McNickle and Brown. Read the below commentary on the paper written by Journal of Ecology Editor Mark Rees. Author Gordon McNickle has also provided some photos, which are at the bottom of this post. The next issue of the Journal will be online very soon.

Blissful indifference or escalation?

Imagine you’re in a dark room and there are diamonds on the floor, some areas have lots of diamonds so you search them carefully, whereas others have few and so you briefly search there. You wander around collecting the diamonds and smugly smiling to yourself, then you realise there is someone else in the room and they’re stealing “your” diamonds! What do you do? You could just do as before, ignore the presence of the other person, and providing they do the same end up with roughly ½ the diamonds or you could start searching frantically trying to increase your share. This is exactly the dilemma plants face when foraging for resources underground.

Let’s assume you start searching more quickly, so you increase your share of the diamonds. Soon your competitor realises what you’ve done and so they search more quickly themselves. At this point you’re both searching more quickly and so you both end up with ~½ the diamonds. You escalate again, now you’re running around frantically searching, your competitor responds in kind, so you’re both running around like ants under a magnifying glass on a hot summer’s day. Bang! Your competitor runs into a wall and passes out losing all their diamonds, a smug grin crosses your face again and is promptly wiped off as you too run into a wall, pass out and lose all your diamonds. So at each escalation you’re spending more energy searching and getting the same return, or ultimately no return at all. This process is called “The Tragedy of the Commons” and was proposed by Hardin as a way of explaining why common land is often overgrazed, and similarly why fisheries are often overfished.

So what do plants do when competing for soil resources? This is the question posed by McNickle and Brown (2014) in this issue’s Editor’s Choice. It turns out that distinguishing between sensibly searching so that your returns from different areas per searching effort are equal (the idea free distribution) and escalating is much more difficult than you might expect. Using a combination of mathematical modelling and experiments with carefully chosen controls, McNickle and Brown (2014) show how to distinguish between these alternatives. They then go on test their ideas experimentally finding that Brassica rapa forages according to  –  well that would be telling, you’re going to have to go read it yourself.

Mark Rees
Editor, Journal of Ecology