Lions and tigers and bears – no more? Dorothy’s trip through the forests of Oz might be a lot less scary these days due to massive losses of the world’s largest predators. But the wipe-out has horrendous implications for the world’s ecosystems – and us, a research team argues in a major new study.
“We now have overwhelming evidence that large predators are hugely important in the function of nature, from the deepest oceans to the highest mountains, the tropics to the Arctic,” says William Ripple of Oregon State University in Corvallis, one of 24 authors of the Science study. “These predators and processes ultimately protect humans. This isn’t just about them, it’s about us.”
In their report, the scientists cite numerous examples of how the loss of top predators has set-off chain reactions that ripple through and reshuffle ecosystems. For example:
- Reduction of cougar in Utah led to an eruption of deer, loss of vegetation, altered stream channels, and a decline in biodiversity.
- Industrial whaling in the 20th century likely caused a killer whale diet shift and a dramatic decline of sea lions, seals and sea otters.
- Decimation of sharks resulted in an outbreak of cow-nosed rays and the collapse of bay scallop fisheries.
- The loss of sea otters allowed herbivorous sea urchins to boom, and munch down kelp forests.
- The reduction of lions and leopards in Africa led to a population explosion in olive baboons, which bring intestinal parasites to humans who live in close proximity to them.
Such disruption is sufficiently severe that it now affects everything from habitat loss to pollution, carbon sequestration, wildfire, climate, invasive species and spread of disease, the scientists write. It is also a driving force in the sixth mass extinction in Earth history, which the researchers say is now under way.
“We propose that many of the ecological surprises that have confronted society over past centuries – pandemics, population collapses of species we value and eruptions of those we do not, major shifts in ecosystem states, and losses of diverse ecosystem services were caused or facilitated by altered top-down forcing regimes,” the scientists write.
The “top-down” force that predators impose on ecosystems, they conclude, “must be included in conceptual overviews if there is to be any real hope for understanding and managing the workings of nature.” – David Malakoff | July 15, 2011
Source: Estes, J., Terborgh, J., Brashares, J., Power, M., Berger, J., Bond, W., Carpenter, S., Essington, T., Holt, R., Jackson, J., Marquis, R., Oksanen, L., Oksanen, T., Paine, R., Pikitch, E., Ripple, W., Sandin, S., Scheffer, M., Schoener, T., Shurin, J., Sinclair, A., Soule, M., Virtanen, R., & Wardle, D. (2011). Trophic Downgrading of Planet Earth. Science, 333 (6040), 301-306 DOI: 10.1126/science.1205106
Image Oregon State University