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The Place Where Ecology Was Born
Seventy years ago at Linsley Pond, a Yale biologist named G. E. Hutchinson started research that has changed the way we think about nature. Today, his scientific heirs are picking up where he left off.
July/August 2004
by Bruce Fellman
Naturalist and science writer Bruce Fellman is the managing editor of the Yale Alumni Magazine.
Late last October, David Post rowed a small metal boat to the middle of Linsley Pond and readied his sampling gear. It was a beautiful afternoon. Post was only a 15-minute drive from the Yale campus, but the scene was straight out of On Golden Pond. There were even loons—although, this being autumn, they were quiet.
The half-dozen undergraduates in Post’s ecology course had already finished their work and come ashore. All that marred the glassy surface of the water were the splashes whenever Post dropped his plankton net or temperature-and-dissolved-oxygen probe overboard.
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“Based on what we’ve learned about Linsley, these critters aren’t supposed to be here.” |
As he worked, Post called out numbers to an assistant. The data—showing cooling temperatures and changes in water chemistry—told a typical story of a lake (biologically speaking, Linsley is not a pond) getting ready for the winter. But when Post pulled up his plankton net and found its collecting jar teeming with pinhead-sized, shrimp-like creatures, he shook his head in disbelief. “This is surprising—really, really surprising,” he said. “Based on what we’ve learned about Linsley, these critters aren’t supposed to be here.”
Post had found a large species of water flea, or Daphnia, one of the biggest kinds of zooplankton. It is common in southern Connecticut but has rarely been recorded in Linsley, where the paleobiological record, in core samples taken from the lake bottom, goes back almost a thousand years. Daphnia’s sudden appearance was an unmistakable sign that the lake’s biggest plankton predator, a species of herring called the alewife—or, in New England, the bucky—had died out.
For an ecosystem the size of Linsley, the demise of the resident buckies is a major event. For Post, a freshwater aquatic biologist, it creates an outstanding research opportunity. Coincidentally, a fish ladder will be built next spring to allow ocean-dwelling buckies to reach the lake for the first time in more than a hundred years. Post will have a deckside seat on one of the most important trends in environmental stewardship of the U.S. coast. He’ll be able to record what happens to a radically altered ecosystem when humans try to return it to its pre-industrial condition. And he’ll be doing it in one of the best-studied bodies of water on the planet—the place where G. E. Hutchinson and his students founded modern ecology.
Linsley Pond is well studied not because it’s biologically unique, or even unusual. It’s an extremely ordinary “kettle hole,” a freshwater lake formed about 13,000 years ago from the melting of giant blocks of ice that were left behind and buried in the wake of glaciers. There are kettle hole lakes throughout the Northeast; this one is oval in shape, roughly a half mile long and a quarter mile wide, with a maximum depth of 44 feet. It is well studied because it was the right place at the right time.
From the 1930s until the late 1970s, the Yale biologist George Evelyn Hutchinson (1903-1991) and a legion of his students, many of them now in the world’s top ranks of ecologists, examined every facet of Linsley—its biology, chemistry, and geological history. In the process, Hutchinson and company discovered some of the general principles that govern living communities. The concepts of biogeochemical cycling, paleobiology, and biodiversity; a method for delineating biological niche; the mathematics of population ecology—all flowed, in part, from Hutchinson’s research at Linsley Pond.
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Hutchinson always rejected the title “father of ecology,” insisting that it belonged to Charles Darwin. |
In a science that depends on reading patterns, says Yale freshwater ecologist David Skelly, Hutchinson “had an uncanny eye for coming up with the pattern that mattered.” Hutchinson always rejected the title “father of ecology,” insisting that it belonged to Charles Darwin. It was one of his students, W. Thomas Edmondson '38, '42PhD, who wrote in 1971 that Hutchinson invented modern ecology, and most modern ecologists would agree. “Everything that is going on about ecology that is exciting can be traced back to ideas he had many years ago,” wrote Edmondson.
A favorite theme of Hutchinson’s was how diversity evolved and persisted. One of his best-known expressions of it was a paper called “The Paradox of the Plankton,” which appeared in American Naturalist in 1961. It drew on early phytoplankton studies at Linsley as well as his work at high mountain lakes in India, desert lakes in South Africa, and elsewhere around the world. At first glance, Hutchinson said, a pond or lake appears to be a homogeneous environment, in which all the phytoplankton compete for the same limited nutrients. The prevailing theory held that in such a uniform medium, there should be few species: “one species alone would outcompete all the others.” But instead, there were many.
The solution lay in his insight that the water was not at equilibrium. It was constantly changing, season by season and year by year. A diversity of plants and animals could evolve to take advantage of these changes. This concept was a turning point for ecology, says University of Washington ecologist Robert T. Paine. “The Paradox of the Plankton” changed the most fundamental assumptions of the science: “We’ve moved from thinking about closed systems to thinking about open systems, from equilibrium to non-equilibrium,” he says.
In another paper still famous among ecologists, Hutchinson and co-author Vaughan T. Bowen '37, '48PhD, described what may have been the first successful use of a radioactive tracer in freshwater biology. “On June 21, 1946,” they wrote in the Proceedings of the National Academy of Sciences in 1947, “a sample of radiophosphorus . was introduced into the surface water of Linsley Pond.” (Hutchinson himself did the introducing. The paper mentions a boat, but the oral tradition among his students is that he swam halfway across the lake with the phosphorus. Today, the element can only be used with high-level radioactivity protection.)
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Before Hutchinson’s experiment, a lake was a black box in terms of its biogeochemical cycling. |
Hutchinson’s aim was to find out what happened to the phosphorus, which was thought to be an important nutrient. By taking water samples at different locations and depths and analyzing them for radioactivity, he tracked the phosphorus from the surface water into phytoplankton and then, as the plankton died (or were eaten) and their remains sank downward, all the way to the lake bottom. From there it was released back into the water column and taken up again by phytoplankton.
Before this experiment, says Skelly, a lake was a black box in terms of its biogeochemical cycling: “Researchers didn’t really know which nutrients mattered in a lake, and trying to determine the important ones was pretty much a dark art.” Hutchinson was the first Western scientist to use the term biogeochemical cycling, and his 1947 paper inspired many other scientists to use radioactive tracers. The paper also showed how quickly phosphorus moved from the inorganic part of the lake ecosystem (water) into the organic part (algae). It led to later research confirming that the amount of phosphorus in a lake limits how much life it can support. And eventually, Tommy Edmondson and other scientists built on Hutchinson’s work when they proved that phosphate pollution caused excess algae growth in lakes.
When Hutchinson first visited Linsley in the early 1930s, the area was still rural and the lake was bordered by a farm. Today, half of the surrounding land remains undeveloped—it is unbuildable ledge and wetland—but the other half of the lake is ringed with cottages.
The biggest change in Linsley’s ecology, however, took place in the late nineteenth century. Pisgah Brook, the stream that flows out of Linsley and eventually joins the Branford River and the Atlantic, was dammed to create a reservoir system. And Linsley lost its springtime run of buckies.
Like salmon, the bucky (Alosa pseudoharengus) typically spends most of its life in the ocean but returns to its birthplace to breed. In the early days of the New England colonies, many streams hosted staggeringly large springtime bucky migrations. John Pory’s 1622 description of the Plymouth colony refers to “infinite schools.” More than one colonist reported runs so dense that rivers could be crossed “dry-shod.”
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Squanto had taught the Pilgrims to use buckies as a fertilizer for corn. |
But not long after the Pilgrims set up housekeeping in Plymouth in 1620, colonists started putting up dams to harness water power. Streams throughout the Northeast were blocked to anadromous (sea-run) species. The sea-run bucky, one of the fish that Squanto had taught the Pilgrims to use as a fertilizer for corn, all but vanished.
In many lakes, a few of the fish were trapped by the dams (or by natural blockages such as fallen trees or beaver dams) and adapted to full-time freshwater life. There are also lakes where, perhaps as part of an ecological management plan, perhaps from someone’s bait bucket, buckies have been dumped into the water deliberately. Instead of a huge springtime influx of fish grown large through ocean feeding, these lakes harbor much smaller, lake-fed fish year-round.
In 1964, a former Hutchinson student, John L. Brooks '41, '46PhD, became curious about whether landlocked buckies had any effect on the kinds and numbers of animals and plants that lived in the water. Brooks enlisted sophomore biology major Stanley L. Dodson '66, and they studied Linsley and a dozen other Connecticut lakes. Some had buckies, some did not.
In “Predation, Body Size, and Composition of Plankton,” a landmark 1965 paper published in the journal Science, Brooks and Dodson reported that when landlocked buckies were present in a lake, relatively big zooplankton such as Daphnia were missing. The only cladocerans (the plankton group to which Daphnia belong) that appeared in the plankton nets were smaller ones, such as Bosmina. But when the situation was reversed and buckies were not present, Daphnia dominated the scene.
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“What has become clear is that coexistence and diversity are driven from the top down.” |
“Fish make a huge difference,” says Robert Paine of the University of Washington, whose research in the 1960s, along with that of Brooks and Dodson, established the importance of predators in controlling the structure of an entire ecosystem. Paine worked in the rocky intertidal area of the Washington coast. There, he removed starfish from the tidal zones, recorded dramatic drops in the diversity of the communities, and established the role of the “keystone” predator. “What has become clear is that coexistence and diversity are driven from the top down,” says Paine.
Today, the concept of the keystone predator is a central tenet of ecology and the scientific basis of efforts to preserve tigers, sharks, and wolves in the wild. Keystones, be they polar bears or buckies, “can have major impacts on the health of an ecosystem,” says Thomas E. Lovejoy '64, '71PhD, a leading conservation biologist (and the first person to use the term “biological diversity”). “When you snip off the top level of the food chain, there can be profound effects,” he says. “Putting it back will also have profound effects.”
About 30 years ago, Yale, like many universities, started to turn its attention away from the biology of organisms and toward biology on the molecular level. Ecology was more or less abandoned. The last research on Linsley was a study of the pond’s geological history over the past thousand years, by Hutchinson grad student Richard B. Brugam '75PhD. By the time Hutchinson died in 1991, all of his students and scientific heirs were working at other institutions.
So no one was looking when the buckies died. Post’s discovery of Daphnia last October was the first definitive evidence. Post, an assistant professor in the ecology and evolutionary biology department that Yale created in 1998, is part of the new wave of Yale ecologists. He thinks Linsley may have gotten too hot for the fish. “My best guess—and this is pure conjecture—is that the weather did them in,” he says. He has seen it happen around the Great Lakes: “In the summer, they can’t live in the lake bottom where there’s no oxygen, and at the top, it’s too warm. If there’s a spell of unusually hot weather, the fish can get squeezed into an increasingly narrow zone of livable conditions. If this zone vanishes, they’re gone.”
The disappearance of the landlocked buckies allows Post to follow up on the work of Brooks and Dodson by watching what happens to the lake when its original keystone predator returns. Next spring, when the Branford River Project’s fish ladder goes in beside the supply-ponds dam on Pisgah Brook, Linsley Pond will be ecologically reconnected to Long Island Sound. In time, the buckies may run again.
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“This is a huge experiment, and we don’t know what’s going to happen.” |
This scenario—the creation of fish ladders or the wholesale removal of dams—is becoming increasingly common in the United States as ecological ideas get a hearing in state and federal government. “Dams create barriers and fragment the system,” says Lovejoy. He is now president of the H. John Heinz III Center for Science, Economics, and the Environment, which is working for a return to free-flowing rivers and streams internationally. “Before the aquatic environment was manipulated by people, it was one long continuous ecosystem,” Lovejoy says.
But the attempt to put back a measure of paradise is no sure thing.
“We are about to open up huge swaths of the freshwater landscape to reinvasion by anadromous alewives,” says Post. “This is a huge experiment, and we don’t know what’s going to happen. Linsley is one place where we’re going to find out.”
One unknown is water quality. In some lakes, landlocked buckies have rearranged the food web to the detriment of the ecosystem. Big plankton filter out algae. In waters polluted with excess phosphorus—which encourages algae growth—a lack of Daphnia means a greater likelihood of algal blooms. When an algal bloom eventually dies and decays, it uses up the oxygen in the lower waters of lakes. The results are often a dramatic, malodorous fish kill and an impoverished environment.
Will the influx of sea-run buckies have the same effect? Or will they change the ecosystem in some entirely new way? Ecologists don’t know. The potential for a problem exists: anadromous fish bring in large quantities of marine nutrients, which could spur algae growth. On the other hand, there is anecdotal evidence that sea-run buckies don’t diminish water quality.
“Landlocked alewives are active in the spring, when zooplankton are first emerging from the sediment,” Post points out. “It might not take very much predation to cap zooplankton numbers at a very low level—effectively nipping any population growth in the bud.” By contrast, sea-run buckies don’t come into the lake until April, and they are there to spawn; food is the last thing on their minds. Their eggs don’t hatch for about a month. The young may not be big enough to have much of a predation effect on the plankton for several more months.
Post and his graduate students are turning subsections of Linsley Pond into mini-ponds to learn more about how the buckies affect zooplankton. They will install several large, impermeable plastic bags, eighteen feet long by six feet across, in the lake. Some of the bags will be filled with anadromous buckies, some with the landlocked variety, some with both, and some with neither. Post and other scientists are also studying the anatomical and genetic differences between the two types of fish, to find out whether they’ve diverged enough over the centuries of dam building that they may no longer be quite the same species.
“This is important work,” comments Lovejoy. “While we know in broad terms how to restore sections of the natural world, there are plenty of details we need to learn. And it’s nice to see we’ll be learning them at what is, after all, a limnological mecca.
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A resurgence of sea-run buckies could have an effect on the ecology of the Atlantic Ocean. |
There are reasons to believe that the net effect of having sea-run buckies in the watershed could be very good. Night herons, cormorants, great blue herons, and other birds show up on lakes and streams with alewife runs. Otters and other mammals take the fish. Moreover, in the coastal ocean, the decline of a fish called the menhaden has left buckies as the dominant prey for striped bass and bluefish. A resurgence of sea-run buckies could have an effect on the ecology of the Atlantic Ocean.
“If we want to understand the dynamics of the system, we have to look beyond it,” says Post. “What happens in Long Island Sound is affected by what happens in Linsley Pond. By itself, it may not matter much, but we’ve dammed hundreds of systems like Linsley, and when we start to remove the dams, build fish ladders, and restore the links in the ecosystem, there may be a profound impact. The growth and dynamics of striped bass in the coastal ocean may be tied to water quality in freshwater ponds.”
The old view that lakes are essentially isolated microcosms has given way to the understanding that lakes—all habitats, in fact—are elements of an interconnected web of landscape and seascape. Out of these interconnections “great diversity” emerges, wrote Hutchinson in a 1964 essay about the nature of lakes. Humans, he said, can “appreciate the diversity, and learn to treat it properly.”
If only Hutchinson were alive today to watch the buckies come back to Linsley, says Post. “He would have loved this.”  |
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