When Large Animals Disappear, Ecosystems are Hit Hard

By Valerie Ross | July 18, 2011 5:01 pm

What’s the News: The loss of large animals is wreaking havoc on Earth’s ecosystems, according to a scientific review published in Science on Friday, causing food chains to fall into disarray, clearing the way for invasive species, and even triggering the transmission of infectious diseases. The decline and disappearance of these large animals, due in large part to human factors such as hunting and habitat loss, has such strong and wide-ranging effects that the review’s authors say it may well be “humankind’s most pervasive influence on nature.”

How the Heck:

  • The researchers reviewed data from recent studies investigating the loss of so called “apex consumers,” large predators and megaherbivores, from terrestrial, freshwater, and marine ecosystems around the world.
  • Whether on land or at sea, the researchers found, the result was the same: Remove the apex consumer and the whole ecosystem suffers, as the initial loss sets off a cascade of changes all the way down the food chain. “Predators have a huge structuring influence,” ecologist Stuart Sandin, one of the researchers, told LiveScience. “When you remove them you change the biology, which is typically profound and complex. And in many cases it’s not necessarily predictable.” While removing an ecosystem’s top dog—or shark, or wolf, or elephant—is bound to have a big impact, just what that impact will be varies widely.

For Example:

  • Wolves. When wolves were extirpated from Yellowstone National Park, elk and deer populations soared—and the ever-more-abundant herbivores ate a huge number of willow and aspen saplings, destroying the habitats of smaller animals and even altering the course of some streams. Likewise, the dearth of wolves across North America means many more deer—which not only gobble up gardens, but carry Lyme-disease-laden ticks.
  • Wildebeest. Outbreaks of rinderpest, a disease that struck livestock and grazing animals, decimated wildebeest populations in East Africa until the disease was eradicated there in the 1960s (it has since been eradicated worldwide). Without large and hungry herbivores, shrubs and small trees proliferated, making it easy for dangerous wildfires to spread. Free from rinderpest, the wildebeest populations went back up; their grazing kept the shrubbery—and the fires—in check.
  • Sea Otters. In coastal ecosystems in the Pacific Ocean, sea otters dined on sea urchins. When the otter populations shrank, the sea urchins multiplied and gobbled up large swaths of the kelp forests growing nearby.

Possible Solutions:

  • One way of addressing the problem is to bring back native species wherever possible. Wolves, for instance, were recently reintroduced in Yellowstone.
  • The disappearance of apex consumers isn’t a new phenomenon. Much of the megafauna that once populated the planet—mastodons, giant kangaroos, saber-toothed tigers—has been extinct for millennia. For buttressing these ancient ecosystems, since the apex consumers can’t simply be brought back, some conservationists advocate rewilding: subbing in modern approximations for the extinct species of yesteryear.

Reference: James A. Estes et al. “Trophic Downgrading of Planet Earth.” Science, July 15, 2011. DOI: 10.1126/science.1205106

Image: US Fish & Wildlife Service

  • E.M. Lores

    As a retired marine scientist, I studied plankton communities in our local bay. I think that the loss of too many fish from our bay has caused a dramatic shift in the basic phytoplankton to pico-cyanobacteria. A type of algae that does not support most organisms in the estuarine ecosystem and therefore significantly reduces the productivity of the system. We need to restore fish populations, but at this point the system will not support them. I think we need studies to investigate how to restore systems when the loss of predators has lead to dramatic changes that are difficult to reverse.

  • Karen

    I wish they would qualify hunting instead of blaming hunting in general. REAL hunting aims at eco-management. It is poachers or those hunting illegally who are destroying the ecosystem. Villainizing all hunting needs to stop.

  • http://discovermagazine.com Susan P.

    I think we should stop breaking ANY new ground ANYwhere – and simply rebuild where structures are now. There are many vacant places everywhere – houses, strip malls, etc. – Why aren’t we reusing all these buildings? Even by me, they are about to start “development” in some fields.. (argh! I hate that word – It sugarcoates it)
    What more can I do, without an environmental background?!

  • m

    Karen – agreed. I would go even further and say hunting should be expanded! Too many people have “Bambi” syndrome. Deer are nothing more than rats with antlers (albeit tasty ones!).

  • Brian Too

    @2. Karen,

    There is no such thing as “real” hunting. Hunting is hunting. In low enough levels all hunting is a minor blip on prey populations. At high enough levels, any hunting at all can be an extinction level event. Eco-management must encompass the idea that hunting must be banned in certain places, at certain times, for certain species.

    I vividly remember an interview published locally, with a hunter. Grizzly populations are in trouble but this guy simply could not accept that “animal needs could be placed above human needs.” In fact this brilliant character couldn’t recognize that the grizzly’s need to exist, as a species, completely trumped his need to shoot them.

    Is hunting then bad? Of course not. However pretending that poaching, overharvesting, and underground economies aren’t “real” could lead to a world where large predator and prey species no longer exist. I don’t want such a world.

    @4. m,

    Your comment equating deer with rats shows that you have little to contribute. Come back when you grow up.

  • Cottereaux

    So how is it that Mother Nature has wiped out hundreds of thousands if not millions of species since life began on Earth including those LARGE dinosaurs yet life goes on? What is the real purpose of this story?

    Seems to me the all these do good environmentalists should just let Nature do its thing, after all, Nature has been at this species extinction thing for over a billion years. That is a lot of practice time!

  • Tim

    @ Cottereaux That is a great point. Mother nature has also regulated the earth’s temperature for millions of years, so we should continue to pump green house gases into the atmosphere and let the earth figure it out. What’s the worst that could happen?

    And hey, human beings have managed to survive for thousands of years before the discovery of “calories” and “vitamins”. People should just ignore silly things like “science”, and just eat whatever they want whenever they want. Things worked out fine in the past, so QED it must continue to work out fine in the future.

  • Travis

    I am no environmentalist nor am I an avid hunter. But in light of the subject at hand it seems that most have not gotten the point of this topic.

    By in large the human race as a species is self preserving and destructive. We take what we want and need and throw away the rest. Through our history we have caused entire eco-systems to fail. Once vibrant forests now reduced to shopping malls, parking lots, and residential housing. We build in places where we encroach on the habitat of other species taking from them their food, water, and shelters. Yes I hunt, yes I fish, but I do so by US federal regulations. I don’t go out and hunt deer when its turkey season and vise-versa. To blame just one or even several groups of humanity doesn’t solve any problems. We as a collective species is at fault for harming this planet the way we have. Yes we haven’t been on this planet for a very long time. But we have been here long enough to do the damage we have.


Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!


80beats is DISCOVER's news aggregator, weaving together the choicest tidbits from the best articles covering the day's most compelling topics.

See More

Collapse bottom bar