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    Going Topless: The Loss Of Top Predators Drives Ecosystem Shifts
    By Holly Moeller | July 11th 2011 06:28 PM | 6 comments | Print | E-mail | Track Comments
    About Holly

    I'm a graduate student in Ecology and Evolution at Stanford University, where I study ecosystem metabolics and function. In particular, I'm interested...

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    I don’t care how long (or short) of a time you’ve spent lounging in the Stanford bubble. If you haven’t popped out yet to see a sea otter, I have an assignment for you: Drop everything and get to the coast. Charismatic fur balls await.

    Today, sea otters are the poster children of cuddle appeal, but their endearing behaviors were lost on the fur hunters of the 1800s. Otter fur lined jackets (and the fur trade lined pockets), but soon otters no longer lined the Pacific Coast.

    The sea otter, however, is a “keystone species” — its impact on our coastal ecosystems is disproportionately large compared to its natural abundance in the marine community — so its removal had profound effects that we only noticed recently, as the otter staged a dramatic return over the last 70 years.

    Otters like shellfish. So much so that where otters live, abalone and sea urchins are rare. Urchins eat kelp,so once otters devour the urchins, kelp grows in abundance. That’s good news from a restoration perspective: the return of the otter has also meant the return of kelp forests, historically “more natural” than rocky urchin barrens. And it makes the seaweed industry happy (kelp products turn up in ice cream and toothpaste, among other things). But plenty of fishermen find the change less palatable: the (now defunct)abalone industry, for example, arose largely because the loss of otters led to a population explosion in the snails. In the sea otter’s absence, we humans partially assumed the role of top predator, a role we’re hesitant to relinquish.

    Although the otter drama has died down, other predator comebacks remain controversial. Wolves, which exerted top-down controls on herbivore populations all across the northern portion of our continent, are slowly (under the stewardship of biologists and conservationists) regaining their ecological foothold in places like Yellowstone National Park. Where once an ecosystem was falling apart at the seams (overgrazing by elk decimated forests, leading to a lack of proper dam-building materials and many unhappy beavers; shifting vegetation changed the face of the park and its complement of animal species), wolves have almost magically stabilized it. For biologists observing the system, the reintroduction of wolves must have been like finding the missing key and unlocking a treasure trove.

    Of course, most of the nearby ranchers would rather the key had been permanently lost. Their treasures are their herds, and wolves are often blamed for any loss of stock. I, for one, am glad the wolves are back to playing their native role — and hoping they extend their range East, to control a deer population explosion that’s decimating my childhood forests. Hiking past the leafless stalks of what should be the next generation of trees, I’m frequently willing to shoot Bambi myself.

    The dramatic and complex effects stemming from the loss of top predators (and the reversals associated with their return) is not unique to these systems. Such “trophic cascades” (“trophic” for food chain, “cascade” for the direct and indirect ripples spreading downward through the system) have been found around the world. As we continue to monitor the accidental experiments created by human impacts, we’ll doubtless find many more examples.

    Will this knowledge help us predict the effects of future species losses?

    Probably not. Ecology is a complex science, and its overriding conclusion is that, well, “it’s complicated.” In some cases, apex predators and their top-down cascading effects rule the system. In other situations,though, the controls are bottom-up, and the community is limited by nutrients, the rate of plant growth or some other fundamental factor. And, because we’re seeing all these systems as snapshots (often heavily impacted by human activity), it’s hard to guess where the real balance between these two regimes lies.

    One thing is clear, though. We are an inextricable part of the system. Of course, we always have been.But before we learned to use oil for cheap energy, before we domesticated crops and settled onto farms, before we organized ourselves into hunter-gatherer clans, our own cascades were much smaller.

    Today, though, we are the keystone species. Our top-down effects cascade through the system when we fish out top predators like sharks or when we shoot the one mountain lion found roaming in Redwood City. Our bottom-up effects transform ecosystem processes when we add fertilizers or pollute landscapes.

    Our ability to modify the world has evolved faster than the world’s ability to deal with our modifications. Of course, there’s a growing feeling that we should try to limit these modifications — not least because they’re putting our future existence on this planet in serious jeopardy.

    Ina few pet systems, especially here in America, we entertain dreams of systems “restored” to the way they “must have looked” before us. But unless our population shrinks dramatically, it will be very hard to avoid pressing all of our accessible land area — and most of our coastal waters — into direct human service.

    So perhaps the real moral from the story of the otter, or of the wolf, is to impose our will with impunity, understanding that ecosystem cascades, like true waterfalls, are incredibly powerful, sometimes beautiful and often impossible to control.

    Holly welcomes fully-clothed reader comments and suggestions via email at hollyvm@stanford.edu.  This column was originally published in The Stanford Daily on May 12, 2011.

    Comments

    vongehr
    A refreshingly balanced view. After the title let me fear the worst, there was none of what I feared would come. Well done. So, you would actually look with some objectivity at imposing our will with impunity as the new top predator?
    hollyvm
    As an ecologist, and as a human, I believe the correct response is, "it's context dependent."  There are plenty of examples in which we're already critical to maintaining ecosystems "as we know them".  And depending on our conservation goals, it's sometimes necessary to cull herds, etc.  But in most cases, I believe reducing human impact, rather than increasing it, is the long-term way to go.  Of course, there's a balance between doing this, and meeting human needs, since with a population of 7 billion, we're already way above Earth's carrying capacity.
    Hank
     There are plenty of examples in which we're already critical to maintaining ecosystems "as we know them". And depending on our conservation goals, it's sometimes necessary to cull herds, etc. 
    You are what we call a 'sane hippie' - and that's good, though I think the carrying capacity of Earth has always been exceeded by its people.  That is how population increases.  Clearly a small tribe 10,000 years ago that was running out of wild game and berries could have talked about mitigation, rationing and culling its members but the scientific minds of the day created domesticated livestock and agriculture and we grew.  Europe led the world for hundreds of years because they created agriculture improvements no one else had and increased their carrying capacity dramatically, and wealth and therefore mass education with it.

    There is no population issue we have today that cannot be solved by energy - water, and therefore crops, can be produced anywhere with better energy technology, and agriculture over the last 30 years has become incredibly efficient.   That energy technology is not here yet but we make enough food already, we just can't distribute it efficiently - because of energy.    And even if we wanted to give every person on the planet a car and a blu-ray player for free we couldn't because we don't have the raw materials, also an energy issue.
    Gerhard Adam
    Clearly a small tribe 10,000 years ago that was running out of wild game and berries could have talked about mitigation, rationing and culling its members but the scientific minds of the day created domesticated livestock and agriculture and we grew.
    You've mentioned this before, but it simply isn't true.  No population under stress of survival "invents" domestication and/or agriculture.  These are the by-products of a well established group whose survival is not at risk.  While I can't claim knowledge of specifics, it seems an unusual move, as well, since it clearly requires more work and effort than traditional methods (although it appears that animals may have been easier to maintain).  Once again, this marks more of a shift in our social organization than our application of intellect.
    There is no population issue we have today that cannot be solved by energy - water, and therefore crops, can be produced anywhere with better energy technology, and agriculture over the last 30 years has become incredibly efficient.
    While true, it is also true that we are uniformly failing to solve this problem.  Population has continued to outpace our ability to address these issues which is precisely why millions upon millions of people end up starving.  We can certainly argue about whether we will ever solve this problem, but given our track record .... I would argue that it isn't likely.  Therefore, we are faced with the reality of a "carrying capacity" whether it be of the Earth or our society's institutions.  Dress it up how you like, but a substantial portion of the world's population will face a life with poor prospects for survival and simply continuing our unconstrained growth seems like a recipe for disaster.  Bear in mind, that this isn't simply an energy issue, but one that will affect and be effected by other organisms and how they interact with us.  By our growth we are changing the conditions of the environment, as well as exerting selection pressures on other organisms to survive as well.  We've already seen on those that can capitalize on human societies tend to do well (cockroaches, rats, etc.).  Others may well have responses for which we have little or no preparation (i.e. disease vectors).

    Mundus vult decipi
    rholley
    Since the red kites were re-introduced in our region, they’ve multiplied and in the last year we’ve regularly seen them from our road.  And we don’t see any more rats in our garden.

    One took off and flew past our kitchen window.  The impact was more like an aircraft than a bird!
    Robert H. Olley / Quondam Physics Department / University of Reading / England
    rholley
    Reading what you said about sea urchins, things are different over here in Europe.

    Sea urchins cannot control invasive seaweeds


    referring to the Mediterranean.
    Robert H. Olley / Quondam Physics Department / University of Reading / England