How to get ahead in an unpredictable world – a Christmas message.

It’s easy to make the right choices in a world that is predictable. For example we plan our holidays around average weather patterns and work schedules. Similarly, animals in the wild, time reproduction to match seasonal increases in food supply. However, if the world is unpredictable, making the right choice is far more difficult. That’s why only a small percentage of investors do well in the stock market.

There are a number of ecosystems that are characterized by highly unpredictable swings in the production of resources. A good example of this is the production of seed by trees in a region. Trees display a phenomenon known as “œmasting” whereby all of the trees in large regions synchronize the production of seed so in a given year trees either produce massive amounts of seed or no seed at all. This is actually an evolutionary strategy by the trees to thwart the animals that eat the trees’ seed. In “bust†years the trees try to starve their seed predators so that in “boom†years there are few seed eaters around and they are swamped by all of the seed available. The seed predators cannot respond in time to the increased production because they cannot predict when it is going to occur. The net result is that more seed escapes to germinate in a mast year as compared to a strategy where the trees produce a constant amount of seed each year.

In this scenario, the seed predators are at the mercy of the trees and they are reduced to simply tracking the resources after they come available. Enter two species of seed predators, the American and Eurasian red squirrels. Our long-term studies (15-20 years) of these species (who forage on the seeds of spruce, pine, oak, and beech trees) indicate that the squirrels are beating the trees at their own game. We found that the squirrels appear to be capable of predicting when a big mast crop is about to be produced by the trees and in anticipation of this, they produce more offspring in the form of an additional litter. So… rather than having to wait for the extra seed to be produced and available for consumption, the squirrels produce more young well before the seed is ready to eat but at a time when the youngsters, once they are weaned, can take full advantage of extremely abundant seeds. The net result is that the squirrels have the maximum number of mouths available to consume the mast crop and in so doing, thwart the trees’ swamp and starve strategy.

The squirrels have had to overcome two obstacles to counter the trees’ strategy. First, they need a reliable cue to predict the upcoming seed crop. Although we do not know what this cue is as yet, we suspect it is tied to the buds which turn into the structures that harbour the future seed (cones for spruce trees, nuts for oak and beech).

The more difficult obstacle to overcome is that the squirrels need to produce the second litter of pups at a time when environmental conditions are very tough; there are no additional resources available to pump into more offspring because the trees have been producing very little seed before the mast year. In this case the squirrels appear to invest in extra offspring not when they can (after seed is available) but when it makes sense evolutionarily (before seed is available but in time for their offspring to benefit). In other words, just as with the trees, natural selection has favored a strategy in the squirrels that leads to more offspring surviving over time. In essence, the squirrels are beating the trees at their own game.

This story is analogous to a family living from paycheck to pay check and facing decisions about how much to spend on the kids’ Christmas gifts. Add to this is the dilemma that the paycheck varies a lot from one month to the next. The tendency in this situation is for the parents to invest only as much as they can spare which would be relatively little if previous months had been tough. However, if the parents could reliably predict that the upcoming paycheck was going to be a big one, they might be willing to “break the bank†to have a good Christmas and the parents can rest easy because they know that there will be money coming in soon. This is what red squirrel mothers are doing but rather than buying presents, they are making more babies.

Stan Boutin
Department of Biological Sciences
University of Alberta
Edmonton T6G 2E9

Luc Wauters
Department Environment-Health-Safety
University of Insubria, Varese

See: Boutin, S., Wauters, L., McAdam, A., Humphries, M., Tosi, G., & Dhondt, A. (2006) Anticipatory Reproduction and Population Growth in Seed Predators. Science, 314, 1928 – 1930. Listed on thePublications web page.

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