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Matt Ridley is the author of provocative books on evolution, genetics and society. His books have sold over a million copies, been translated into thirty languages, and have won several awards.

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Wolves versus lesser predators

The return of top predators is good for prey eaten by "mesopredators"

My latest Mind and Matter column at the Wall Street Journal is on wolves and "mesopredators":

The return of the wolf is one of the unexpected ecological bonuses of the modern era. So numerous are wolves that this fall Wisconsin and Wyoming have joined Idaho and Montana in opening wolf-hunting seasons for the first time in years. Minnesota follows suit next month; Michigan may do so next year. The reintroduced wolves of Yellowstone National Park have expanded to meet the expanding packs of Canada and northern Montana.

The same is happening in Europe. Wolf populations are rising in Spain, Italy and Eastern Europe, while in recent years wolves have recolonized France, Germany, Sweden and Norway, and have even been seen in Belgium and the Netherlands. Nor are wolves the only "apex predators" to boom in this way. In the U.S., bears and mountain lions are spreading, to joggers' dismay. Coyotes are reappearing even within cities like Chicago and Denver.

The effect of top predators on lesser predators, like foxes, raccoons and skunks, not to mention domestic cats, can be devastating. Wolves may kill deer and cows, but they also kill these smaller "mesopredators"-middle-of-the-food-chain carnivores. That may be good news for other creatures, especially birds. The very presence of large predators can intimidate the mesopredators: In the Bahamas, large groupers cause small ones to spend more time in hiding, allowing smaller reef fish to thrive.

In 1988 ecologists coined the term "mesopredator release" for the theory that the original disappearance of apex predators at the hand of human beings had caused a population boom in small opportunistic predators and omnivores. In Africa, for instance, baboons have boomed where leopards have been exterminated, to the detriment of antelopes as well as crops. In one marine case, overharvesting of Atlantic sharks caused an expansion in the number of rays, which in turn hurt the stocks of scallops.

Now, as exemplified by the wolf, top predators are returning little by little. This is due to legal protection and the increasing retreat of people to cities and suburbs (teenagers who play computer games would once have staked out wolf kills to protect the family's herd).

So is the return of top predators now suppressing rather than releasing mesopredators?

In parts of Europe, introduced American mink have harmed birds, water voles and other waterside wildlife. But now newly abundant predators of mink, once devastated by DDT, have caused mink populations to fall. In Finland sea eagles are hunting mink; in Britain otters are.

Complicating the picture, some species can be either apex predators or mesopredators. In Yellowstone National Park, coyotes are mesopredators that appear to have declined at the paws of wolves, which is good news for rodents and other creatures. But in suburbs the coyote is more like an apex predator, whose return lays waste the domestic cats that kill so many birds. Even in rural areas, the coyote is an efficient predator of foxes, skunks and badgers. So the arrival of coyotes in an area may be bad for rabbits but good for birds.

Likewise, raccoons are usually a classic mesopredator, but controlling their numbers in Florida to save turtle eggs from their depredations proved counterproductive, because egg-eating crabs then thrived.

Ecology is a complicated and unpredictable business. To test whether the revival of large predators is generally good news for ecosystems, Dr. Laura Prugh of the University of Alaska at Fairbanks is setting out to compare coyote, fox and lynx populations in an area with intensive wolf control, compared with nearby Denali National Park and Preserve, where wolf populations are intact. As she and her co-writers said in a recent paper, given what programs to control mesopredators cost, letting apex predators thrive may provide an "ecosystem service" by controlling them cheaply and more effectively.