Large predators like sharks, lions and wolves are on the decline worldwide, a trend that is disrupting the Earth's ecosystem in all kinds of unusual ways, researchers said Thursday.
"These predators and processes ultimately protect humans. This isn't just about them, it's about us," said William Ripple, a professor of forestry at Oregon State University and co-author of the report in the journal Science.
The planet is currently in the midst of the sixth mass extinction, said the study by scientists from 22 different institutions in six countries.
But this one differs from previous ones because it is entirely driven by human activity -- through changes in land use, climate, pollution, hunting, fishing and poaching -- and is focused on large, or apex, predators.
"The loss of apex consumers is arguably humankind's most pervasive influence on the natural world," said the study.
The effects can be seen in the oceans and on land.
For instance, fewer cougars in the western US state of Utah led to an explosion of the deer population. The deer ate more vegetation, which altered the path of local streams and lowered overall biodiversity.
Another example came from Africa, where lions and leopard are being lost to poachers, leading to a surge in the numbers of olive baboons who are transferring intestinal parasites to human who live nearby.
In the oceans, industrial whaling in the 20th century led a change in the diets of killer whales, who eat more sea lion, seals and otters and dramatically lowered those population counts.
The loss of big predators has likely driven many of the pandemics, population collapses and ecosystem shifts the Earth has seen in recent centuries, and deserves further study in the future, the article said.
"By looking at ecosystems primarily from the bottom up, scientists and resource managers have been focusing on only half of a very complex equation," said lead author James Estes, professor of ecology and evolution at the University of California at Santa Cruz.
"These findings demonstrate that top consumers in the food web are enormous influencers of the structure, function, and biodiversity of most natural ecosystems."