Why top predators matter: an in-depth look at new research

Jeremy Hance
mongabay.com
February 02, 2010



Three recent studies reveal just how important top predators are to their ecosystems.

Few species have faced such vitriolic hatred from humans as the world's top predators. Considered by many as pests—often as dangerous—they have been gunned down, poisoned, speared, 'finned', and decimated across their habitats. Even where large areas of habitat are protected, the one thing that is often missing are top predators.

However, new research over the past few decades is showing just how vital these predators are to ecosystems. Biologists have long known that predators control populations of prey animals, but new studies show that they may do much more. From controlling smaller predators to protecting river banks from erosion to providing nutrient hotspots, it appears that top predators are indispensable to a working ecosystem.

Not easy being a top predator


Male lion in Kenya. Photo by: Rhett A. Butler.
Top predators sit at the apex of an ecosystem's food chain. Wolves in Alaska, tigers in Siberia, lions in Kenya, white sharks in the Pacific are all examples of top predators. Some top predators have been introduced by humans, such as dingos in Australia, while others have taken over after humans have extirpated the ecosystem's natural top predators, such as coyotes in the US after wolves and mountain lions vanished. Either way, the expanse and population of top predators has changed drastically as humans have taken over the world.

In the continental United States genetic evidence shows that there were once 200,000 wolves when Europeans arrive; today there are less than 5,000. Despite millions of dollars and years of conservation effort wolves are only present in 5 percent of their historic range in the US. Wolverines, though largely a scavenger, are terrific hunters in their own right (they are even known to harass both wolves and mountain lions). But they have it even worse in the US than wolves. While there are only an estimated 500 wolverines in the continental US, the Bush Administration denied them any coverage under the Endangered Species Act stating that wolverines still thrived in Canada, essentially arguing that this predator was unworthy of protection.

The world's largest cats—tigers—are endangered throughout all of their range. Despite being one of the world's most recognizable, and beloved, animals, tigers are on the edge of extinction. The species is classified as Endangered by the IUCN Red List, while two of the six surviving subspecies of tiger are considered Critically Endangered. Few animals have received the amount of conservation attention and funds as tigers, yet every year the great cat moves further from a comeback. Recent reports show tiger populations dropping in both India and Russia, both of which were considered the bright spots in tiger conservation.

Even when top predators bring in millions in tourist revenue—such as is the case of lions in Africa—they still face a barrage of trouble. Habitat loss, poisoning, and killing by gun or spear has crippled African lion populations. Recent reports state that they could vanish altogether from some of their best habitat—i.e. Kenya's grasslands—in twenty years if nothing is done.

To think such species are somehow immune to extinction is erroneous: three tiger subspecies (the Javan, the Bali, and the Caspian), two wolf subspecies (both from Japan), one lion subspecies (the Barbary), and the thylacine—once apex carnivore in Australia—all vanished during the 20th Century. This past decade has seen the loss of the baiji: top predator and river dolphin of China's Yangtze River.


The Critically Endangered Sumatran tiger in captivity. Photo by: Rhett A. Butler.
Other top predators linger on the edge of extinction: the Amur leopard, the Indo-Chinese tiger, the Arabian leopard, the Javan leopard, and the Asiatic cheetah could all vanish during this century. In some parts of the world populations of large mammalian carnivores have dropped a staggering 95-99 percent.

It's not just on land where top predators are vanishing. In the oceans, many shark populations have been decimated. Overfishing, by-catch, and 'finning' (whereby fishermen cut off a shark's fin and then dump the animal back in the water, where it soon succumbs) are all taking a toll on some shark species. A study in 2006 found that up to 73 million sharks are killed by fining in a single year—all this to keep up orders of the Asian delicacy: shark fin soup. The first global survey of sharks and rays found that nearly one-in-three species are threatened with extinction, higher even than amphibians, which are said to be in the midst of an extinction crisis. Some shark species populations have plummeted by over 90 percent in just a few decades.

At a time when top predators are vanishing worldwide, three recent research papers show a very new side of top predators. Peeling off the dangerous, fierce veneer, these studies show that top predators are actually protectors of many aspects of the ecosystems they inhabit and show just how many detrimental ecological ripples their losses entail.

'My enemies' enemy is my friend'

It has long been known that top predators affect and control populations of prey species (such as wolves and elk, lion and zebra, tigers and deer), but recent studies have shown that top predators also affect carnivorous species just one rung beneath them on the food chain, known as mesopredators. Coyotes in North America, hyenas in Africa, ocelots and jaguarundis in South America, and weasels in Europe are all examples of mesopredators.

The rest of this article is now only available to subscribers. An updated version is also published in Jeremy Hance's book, Life is Good: Conservation in an Age of Mass Extinction, which was released in January 2012.





Citations: Euan G. Ritchie and Christopher N. Johnson. Predator interactions, mesopredator release and biodiversity conservation. Ecology Letters. Volume 12, Issue 9.

Beschta, R.L. and W.J. Ripple. Large predators and trophic cascades in terrestrial ecosystems on the western United States. Bological Conservation.

Bump, J.K., Peterson, R.O., & Vucetich, J.A. 2009. Wolves modulate soil nutrient heterogeneity and foliar nitrogen by configuring the distribution of ungulate carcasses. Ecology. Vol 90, Issue 11.







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CITATION:
Jeremy Hance
mongabay.com (February 02, 2010).

Why top predators matter: an in-depth look at new research.

http://news.mongabay.com/2010/0202-hance_toppredators.html