Study Shows Loss of Large Predators Leads to Widespread Disruption

A new study, compiled by an international team of scientists, shows that the decline of large “apex” predators has disrupted ecosystems all over the world.

The study, which is due to be released in the July issue of Science magazine, features a look into the importance of sharks in coral reef systems.  During a multi-year examination of shark populations in the central pacific, Dr. Stuart Sandin noticed great differences in ecosystems between islands. On one uninhabited island named Jarvis, a healthy shark population resided over a virtually pristine reef system. However, on a nearby island, Christmas Island, the increasing population and fishery has decrease shark populations, while also ruining the reef.

"Practically and ethically, we cannot conduct large experiments to investigate the effects of predator removal," said Dr. Sandin. "But in the Line Islands we can rely on a natural experiment to follow what happens when sharks are removed. The abundance of prey changes, the way the energy flows through the ecosystem changes and even the way nutrients are cycled is altered. The importance of this paper is its recognition that predator removal is a global phenomenon, affecting reefs and almost every other ecosystem."

Sandin’s work with sharks was combined with half a dozen other terrestrial, marine, and freshwater studies to assess the impact of losing predators on a worldwide scales. Other studies included the declination of wolves in Yellowstone, reduction of lions and leopards in Africa, decimation of wildibeasts, and the importance of sea otters in kelp forests.

"Predators have a huge structuring influence," said Sandin. "When you remove them you change the biology, which is typically profound and complex. And in many cases it's not necessarily predictable."