April 2, 2013 — We tend to think of evolution as a slow path. It’s something that happens over hundreds of thousands of years. It’s a force that treats millions of years like the blink of an eye.
But that’s not always the case.
In March of this year, the cliff swallows of southwestern Nebraska made headlines after researchers found that this population appeared to be adapting to highway traffic. Over the course of just 30 years, the average wingspan of these birds got shorter. Meanwhile, individuals with longer wingspans appeared to have a greater risk of being hit by a car. Most importantly, as the average wingspan got smaller, the number of swallows dying at the grill of a moving vehicle also decreased.
Disruptive environments can happen without human intervention, but we are particularly good at creating them.
That’s just one study, but it’s part of a growing body of research that suggests evolutionary adaptation can happen much faster than we thought — and that human beings can play a role. It’s all about disruptive environments; what happens when the system a species lives in changes relatively quickly and in big ways. For instance, David Reznick, an evolutionary biologist at The University of California–Riverside, told me that there are dozens of studies suggesting that modern commercial fishing, especially the advent of technologies like motor-driven nets, have changed fish populations. Over the course of a few generations, multiple species have shown trends towards earlier sexual maturity and reaching maturity at much smaller sizes. Those skills allow the species to survive, but make the fish less useful to us as food.
Disruptive environments can happen without human intervention, but we are particularly good at creating them. Whether you’re talking about the construction of a highway or the arrival of a fishing fleet, Reznick told me that dramatic environmental shifts spur localized populations to change very quickly. And those changes can even create new species or subspecies, all within the span of tens to hundreds of years.
This has big implications for environmental science. For one thing, it should change the way we think about invasive species. After all, what’s more disruptive than dropping an animal into an entirely new environment? Reznick told me that the invasive animals and plants often end up very different from the relatives they left behind in the old country. And that is exactly the thing that makes them so difficult to remove from their new homes — they’ve adapted. After a few generations, the new environment isn’t really all that foreign.
But in the bigger picture, this knowledge should also affect how we think about environmental science as a whole. “Traditional ecological theory assumes that evolution does not happen,” Reznick said. “Not because they don’t believe in it, but because they think it’s so much slower than ecology that it can be ignored.”
Ecology is a science of systems — how different species interact with each other and with their habitats. If evolution plays a part in that dance, acting on the systems within human lifespans, then we might be reaching incorrect conclusions about the effects of change.
In other words, it’s not just about how the highway reduces bird populations and affects the food web. It’s also about how the birds adapt to the highway, and what effects those adaptations have on the bigger system. Do swallows with short wingspans eat different things than their wider-winged siblings? If we aren’t paying attention to adaptation, then we don’t even know to ask that kind of question. The systems of ecology aren’t just complex. They’re even more complex than we give them credit for.