When you pick up your fork, are you making the food supply more stable, or are you contributing to ecological collapse?

That's one question Jen Dunne, my colleague at the Santa Fe Institute, and a team of archaeologists and ecologists are asking. They're working with the Sanak Aleut people in Alaska to quantify — for the first time — the complex ways people fit in with all the living things around them.

Until they moved to the mainland, people had occupied Sanak Island in the Aleutian Islands of Alaska continuously for about 5,000 years as hunter-gatherers, meaning that Dunne and her colleagues have a lot of data on a society that interacted with its ecosystem in a relatively easy-to-analyze way. Among the researchers' preliminary findings: Although the Sanak Aleuts ate a variety of foods, they kept their environment stable by switching what they ate from time to time.

In our agriculturally advanced society, the economics of how we eat tends to cause us to do the opposite. We drive animals like the bluefin tuna, popular in sushi, close to extinction. Worse, depleting one species such as bluefin tuna might take an entire ecosystem down with it, making the rest of our food supply vulnerable.

To understand why, it's necessary to think about what eats what, and how people fit in that equation. We humans like to think we are now, and forever will be, at the top of the food chain, invulnerable. If we eat all the cows, there's always salmon, and if we eat all of them, there are always vegetables.

The reality is different. The food chain we learned about in grade school turns out to be inadequate for understanding our food supply. Scientists now understand that we're part of a complex system of interconnected food chains called a food web.

In a food chain, things are simple: A person eats a rabbit, and a rabbit eats a carrot. In a food web, people eat rabbits and cows and pigs, and the things the rabbits and cows and pigs eat, like carrots, lettuce and wheat. Not only that, it's not so lonely at the top. New Mexico's bears, for example, eat some of the same things we eat, and not many things eat them.

Because living things in a food web have options, food webs can make things more stable. If we run short on beef, we can eat more chicken until the cattle population recovers. But the complex connections between different plants and animals mean that if one plant or animal gets too rare, it could set off a chain reaction that wreaks havoc on all kinds of life, including us.

That's where the Alaska study comes in. Using data collected through interviews, studying archaeological sites, and observing wild plants and animals, Dunne is reconstructing the entire ecosystem of Sanak Island over the last 5,000 years, including how people have fit in to that ecosystem, and they're starting to get clues about how the people there minimized their negative impact on the natural environment.

One of the most important Sanak Aleut habits is switching it up, just like other predators do. When the salmon population got low, they hunted for sea lions, and the reason is simple — salmon were harder to find. Switching what they ate every so often had a profound effect. By eating less of the harder-to-find plants and animals, those things had time to recover, so no population ever got too low. In other words, mixing it up meant the ecosystem always stayed healthy.

These days, Dunne says, there's a different reason people hunt: money. Bluefin tuna were recently in the news because, as their supplies run low, fishermen can make more money hunting them, driving their numbers ever lower. But it's worse than that. Because of the complex relationships in food webs, depleting one animal might cause ripple effects that could devastate entire ecosystems. For example, scientists know that sea otters eat sea urchins, and sea urchins eat kelp, so that by eating sea urchins, sea otters helped keep the kelp population afloat. The sea otter population in the Pacific Northwest, however, is in decline — possibly because orcas are eating them in increasing numbers — leading indirectly to kelp deforestation, which in turn hurts scores of creatures like snails, fish and even humans that eat kelp or live in kelp forests.

So, next time you're sitting down for dinner, look at what's on your plate and ponder where it fits in the food web. What you and I and our neighbors eat a lot of tonight and tomorrow and the rest of this year can help decide what we have left to eat next year.

Nathan Collins is an Omidyar Fellow at the Santa Fe Institute and holds graduate degrees in physics and political science. He currently studies how voters' choices change over time as well as topics in evolutionary biology. When not researching weighty scientific matters, Collins is a science writer for publications such as New Scientist and Scientific American Mind.