A new study sponsored by the national science foundation describes a manuscript that just appeared in Science. From the NSF write-up:
“The top-down effects of apex consumers in an ecosystem are fundamentally important, but it is a complicated phenomenon,” Estes said. “They have diverse and powerful effects on the ways ecosystems work, and the loss of these large animals has widespread implications.”
Estes and co-authors cite a wide range of examples in their review, including:
The extirpation of wolves in Yellowstone National Park led to over-browsing of aspen and willows by elk; restoration of wolves allowed the vegetation to recover.
Dramatic changes in coastal ecosystems followed the collapse and recovery of sea otter populations. Sea otters maintain coastal kelp forests by controlling populations of kelp-grazing sea urchins.
The decimation of sharks in an estuarine ecosystem caused an outbreak of cow-nosed rays and the collapse of shellfish populations.
In a similar vein, though whales are not apex predators, there are many new articles and reports with details about why having such large creatures in the ocean is important. One main reason is whales are very effective at churning water and producing fertilizer. New Scientist has an article on this (you may have to register):
http://www.newscientist.com/article/mg21128201.700-vital-giants-why-living-seas-need-whales.html?full=true