The quote from Dobzhansky, that “nothing in biology makes sense except in the light of evolution” has probably been used too many times since 1973, but still I would argue that the average ecologist doesn’t think about evolution on a daily basis. That’s started to change in the last ten years or so, as more studies use experimental data to show that evolution can alter ecological scenarios. To a large extent, that field of study has been led by a large group of researchers from Cornell (Nelson Hairston, Jr., Steve Ellner, Monica Geber, Takehito Yoshida, Laura Jones, Gregor Fussman, and several others) that have nicely used a combination of theory and experiments to make their point.
In virtually every ecology class in the world, students learn about predator-prey cycles…often using lynx and snowshoe hares as an example. The idea goes like this: when there are few predators, prey numbers increase. As prey increase, predators will increase also, up until a point where there are so many predators that prey numbers decline, which eventually causes predator numbers to decline as well. Because “ecology” takes a little while to happen (it takes some time for predators to convert the energy from the food they just ate into little baby predators), the predator cycle lags behind the prey cycle, theoretically by ¼ of a cycle.
In the early 2000’s, the Cornell group showed that if you let prey (green algae) evolve, it alters interactions with predators (rotifers) and throws off those classic predator-prey cycles. I always use this example in presentations because a) it’s really cool and well-done research and b) it helps to explain what I find in my own system. On the other hand, part of me has always thought that this is just a manufactured example of how this could occur, but not really evidence that this commonly occurs in most communities.
But a recent paper in Ecology Letters from the same group changed my mind about that last part. The Cornell group examined lots of published examples of predator-prey cycles and found that the “classic” cycles that we all teach about aren’t common at all. They developed an Evolutionary Dynamics Index (everybody likes an index!) that measures whether the predator-prey cycles have shifted from the classic pattern towards the anti-phase dynamics that should occur if evolution has a big effect. The EDI was significantly different from zero for half of the datasets they analyzed. Even more cool, the EDI tends to be higher when the prey population size is large or the study follows more generations. Both of those scenarios allow more time for mutations to occur, for selection to act on those mutations, and for evolution to occur. Cool, right?
The only drawback in generalizing this result is that all of the published studies are in relatively microscopic systems (bacteria, algae, mites, etc.). Those communities have a natural proclivity for evolutionary effects, just because of their short generation times. In practicality though, these are the easiest systems in which one can measure lots of predator-prey cycles in a reasonable amount of time. But just because these sorts of things are harder to measure in macroscopic systems, doesn’t mean that evolution isn’t also important there. So maybe that Dobzhanskzy quote isn’t as overused as I thought?
