The Human Lake

The Loom
By Carl Zimmer
Mar 31, 2011 9:25 PMApr 6, 2023 6:54 PM

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I went recently to San Francisco to give a talk to a conference of scientists. The scientists were experts in gathering together mountains of biological data—genome sequences, results of experiments and clinical trials—and figuring out how to make them useful: turning them into new diagnostic tests, for example, or a drug for cancer. The invitation was an honor, but a nerve-wracking one. As a journalist, I had no genome scan to offer the audience. We science writers do have one ace in the hole, though. Instead of being lashed to a lab bench for years, carrying out experiments to illuminate one particular fold in one particular protein, we get to play the field. We travel between different departments, different universities, different countries, and—most important of all—different disciplines. And sometimes we see links between different kinds of science that scientists themselves have missed. Which is why, when I arrived in San Francisco, walked up to the podium, and switched on my computer, I presented my audience with this photograph of a lake. For the next hour, I tried to convince them that their bodies are a lot like that lake, and that appreciating this fact could help them find new ways to treat diseases ranging from obesity to heart disease to infections of antibiotic-resistant bacteria. The lake, called Linsley Pond, is located in southern Connecticut, a short drive east of New Haven. It's about a half a mile wide. It supports a typical assortment of species, including algae and bacteria, water fleas, lily pads and other aquatic plants, birds, turtles, and fishes. It looks utterly ordinary. But in the history of ecology, it's one of the most significant places on Earth.

If you were to have gone to the lake 70 years ago, you might have seen a gentleman swimming across the lake, holding a container of radioactive phosphorus, which he then dumped into the water. The swimmer’s name was G. Evelyn Hutchinson. Hutchinson is generally considered by ecologists to be the father of modern ecology. Before Hutchinson, ecology was, to a large extent, natural history. Naturalists would go out into the wild, catalog different species, and make a few observations. After Hutchinson, ecology became a science based on theory, based on mathematics, a science that asked fundamental questions about how nature works.

Lakes turned Hutchinson into a theoretician. They were like self-contained worlds, and Hutchinson was fascinated by the way different lakes in the same region could support different ecosystems. After he came to Yale in 1931, he began making regular trips to Linsley Pond with his students to run experiments, to figure out why this one lake had its particular balance of species. Hutchinson made Linsley Pond his laboratory flask. Hutchinson and his students envisioned the life of Linsley Pond as embedded in an interplanetary flow of energy. The energy starts 93 million miles away, in the heart of the sun. It then hurtles through space, reaches Earth, plows through the atmosphere, and smashes into molecular traps laid out by the plants and algae in Linsley Pond.

The organisms tuck away some of that energy in their cells, while some of it is released as heat. Hutchinson and his colleagues traced the energy as it continued its flow through the lake’s ecosystem, as grazing zooplankton ate the algae, as larger animals fed on the smaller ones, as they died and were, in turn, scavenged by worms and bacteria. As complicated as this diagram may look, Hutchinson knew that it was a faint shadow of the full picture. It's not as if there is just one species of zooplankton. There are about 200 species of zooplankton, and maybe 1,000 species of algae. Hutchinson realized that this diversity presents a paradox. Why should each part of a food web have so many species, rather than just one? Why doesn’t one species outcompete all the others for that spot? Why do we have food webs, instead of food chains? The answer Hutchinson came up with is that species slice up an ecosystem in many ecological niches. People had talked about ecological niches before Hutchinson, but they used the word pretty crudely. A niche might just refer to the place where a particular species lived—where on a mountainside you might find a flower growing, say. Hutchinson had a much more sophisticated idea, one that shaped how ecologists think about diversity ever since.

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