Trophic Cascades: Why sharks matter

David Shiffman in Delancey Place:

The ripple effects that come from the removal or diminished size of a predator’s population:
“Sometimes the ecological effects resulting from changes in predator populations ripple through the food chain. This ripple effect is called a trophic cascade. The classic example of a trophic cascade comes from the Pacific Northwest. When orca whales began to consume more and more sea otters in the kelp forests of the North Pacific, it wasn’t surprising that sea otter populations declined. But the plot thickened! One of sea otters’ favorite foods is the sea urchin, which they consume by adorably crushing them with rocks on their bellies. The population declines of sea otters then resulted in sea urchin preda­tion release. The increasing sea urchin population ate more and more of their preferred food, seaweeds called kelp, resulting in kelp declines. All of this was caused by a change at the top of the food web. Even though area whales and otters don’t eat kelp, changes in how orcas interact with otters significantly affected kelp. And that was bad for everything that lived in the kelp forest.

“The most famous example of a trophic cascade in a terrestrial ecosys­tem occurred in Yellowstone National Park as a result of wolf declines. Fewer wolves meant an increase in the wolf prey population, including giant herbivores like elk. More elk meant more grazing, and perhaps most impactfully, grazing in areas where elk were previously afraid to graze, such as riverbanks that restricted their ability to run away from a predator. This led to major disruptions in a unique Yellowstone ecosys­tem called an aspen forest. The Yellowstone case study also remains one of the best examples of predator restoration: when wolves were even­tually restored, they ate more elk, bringing the population back under control and pushing elk back to their normal feeding grounds. As a result, the aspen forest is growing back.”

More here.