Extinction May Spread from Predator to Predator Instead of from Prey

Extinction may actually spread from predator to predator. Scientists have found that the extinction of one carnivore species can trigger the demise of fellow predators.

In this latest study, the researchers examined insects. They set up experimental communities with complex food webs in 40 four-square meter outdoor field cages. These cages were watched over a spring and summer season, and consisted of several species of aphids and their natural enemies, parasitoid wasps.

Surprisingly, the researchers found that removing one wasp species actually led to an increased rate of extinction in other species of wasp. This effect was transmitted through changes in density of the aphid species.

So what was happening? When one wasp species was removed, its aphid-prey grew in numbers. This, in turn, crowded out other aphids and made it difficult for other wasp species to locate their particular food resources, eventually leading to their extinction.

"This is a unique experiment," said Dirk Sanders, one of the researchers, in a news release. "Usually these research questions are tackled with theoretical approaches and researchers focus on extinctions after the loss of food species. This is the first time anyone has looked at mechanisms of horizontal extinction cascades in a natural large field experiment. Such extinction cascades are seen as a major threat to biodiversity but it is very hard to get data about this happening in nature, due to the many different influences."

The findings reveal a bit more about this particular type of extinction and show that when predators disappear, other predators can suffer.

The findings are published in the journal Current Biology.

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