Analysis: What Wolves Can Teach Us About Covid and the Economy

Covid-19 and the economy have entered into an unsettling relationship familiar to scientists who study animal populations. Covid is the predator and the economy is the prey.

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Consider a classic natural experiment. Sometime in the early 1900s, moose showed up on Isle Royale—a remote island in Lake Superior that is now a national park—either getting there on their own or carted there by people keen to start a new hunting ground. In the winter of 1949, wolves clambered across an ice bridge from Ontario, setting off a predator-prey relationship that scientists have been studying since the late 1950s. When the moose flourished, a surfeit of easy prey led the wolf population to increase. When the wolves ate more moose, the moose population would decline and, eventually, so too would the number of wolves.

Models of the interplay between predator and prey rely on a family of equations that population ecologists have been using for nearly a century. Other fields have borrowed the math. Michael Feroli, an economist at JPMorgan Chase, first encountered predator-prey equations as a college student, and they opened his eyes.

"That was the first time I was like, 'Oh, this math stuff is really neat,'" he says.

They came back to him when he started thinking about the interplay of Covid and the U.S. economy. In the teeth of the Covid crisis this spring, businesses shut down, people holed up at home and the economy experienced a massive contraction. Covid cases dipped as a result. States, to varying degrees, reopened, people became less cautious and the economy rebounded. Not long after, so did Covid. States in hot spots such as Texas have reintroduced some restrictions, while others where case counts have risen this summer are mulling their next moves. The wolf came back.

"The best way to relieve the prey is to make the predator go extinct," says Marc Lipsitch, an epidemiologist at Harvard's T.H. Chan School of Public Health, of the predator-prey model's bearing on what is happening now. But absent an effective vaccine and vaccination program, Covid isn't about to go away. The next best thing for the economy, Mr. Lipsitch says, is adaptation—what prey animals do in response to predation over eons of evolution.

For the economy, that could mean better adherence to mask mandates or tighter restrictions on bars and other gathering places. Mr. Lipsitch's colleague Michael Mina has been advocating for the mass distribution of at-home Covid tests as a way to drive cases down. Neel Kashkari, the president of the Federal Reserve Bank of Minneapolis, has said the answer might be to "lock down really hard" to bring the pandemic under control.

Sarah Hoy, a scientist at Michigan Technological University who is part of the team engaged in the Isle Royale wolf-moose study, points out that delayed responses on the part of predator or prey to changes in the other species's population makes predator-prey systems less stable, with larger peaks and crashes. The lesson, then, might be that the sooner people respond to a resurgence in Covid, the less precipitous the decline in the economy will be. "If you shorten the period of delay, that can really dampen the effect on the system," she says.

Another lesson from Isle Royale, says Ms. Hoy, is that the longer that officials take to respond to instability in a predator-prey system, the more costly it can be. On Isle Royale, it was the predators that needed help. A decade ago, the wolf population began a precipitous decline. If officials had acted then, they might have restored the population by introducing only a couple of wolves to the island. Instead, they delayed, and have relocated about 20 wolves to the island over the past two years. As a result, the island's forests suffered severe damage from moose browsing.

The analogy holds for the economy. Acting in a timely manner to stem the pandemic's spread and the economic damage it is causing could be a lot easier than restoring the balance later. Allowing "nature to take its course" isn't always the best choice for the economy or for actual natural settings like Isle Royale.

One important difference between the predator-prey dynamics that have played out on Isle Royale and the interplay of Covid and the economy is that, unlike wolves and moose, people have foresight.

"Maybe we humans are smart enough to say, 'Hey, we can't reopen like we did in May,'" says JPMorgan's Mr. Feroli. "We can't do the same thing and expect different results."

Write to Justin Lahart at justin.lahart@wsj.com