The Coupling of People and Nature

Traditionally, ecologists have viewed humans in an ecosystem as something of a nuisance — contaminating samples, skewing data and clouding scientific analyses. “But the human aspect of an ecosystem is crucial,” said Jianguo Liu, who leads the International Network of Research on Coupled Human and Natural Systems, or Chans-net, a network of 1,300 ecologists, economists, and sociologists.

“The central message of Chans is that humans and nature are coupled, just like husband and wife,” says Dr. Liu, director of the Center for Systems Integration and Sustainability at Michigan State University. “They interact, work together, and the impacts are not just one way. There are feedbacks.”

The Tonle Sap project is designed to capture those interactions and look for their consequences, often unintended. For instance, increased fishing could actually lead to more fish in the lake, at least for a while. Kevin McCann, an ecologist at the University of Guelph in Ontario, says that if fishermen take everything they bring up in their nets, the species that suffer most will be the larger fish that grow and reproduce slowly. With fewer big fish eating the fast-multiplying, small fish, the results will be more fish over all, but reduced biodiversity.

Over the past decade, data suggest that the lake has been losing its biggest fish — quarter-ton catfish, stingrays with six-foot wingspans, Siamese carp bigger than the fishermen who caught them — while the catch of the tiny trey riel, or money fish, has risen slightly. (They are used primarily for prahok, the fermented fish paste that is a staple of Cambodian cooking.)

Climate models forecast longer, hotter dry seasons for Southeast Asia, and more intense monsoon floods. Both changes could disrupt the migration and spawning patterns of Tonle Sap fish, said Sovan Lek, an ecologist at Paul Sabatier University in Toulouse, France, who is a native of Cambodia and a principal investigator in the Tonle Sap project. “In Europe, the water can go from very cold to very warm, from winter to summer,” he said. “Here, the temperature is stable over the whole year, so adaptation to a change will be more difficult.”