Monday, August 1, 2011

Aldo Leopold and the Mark of the Wolf’s Tooth by Cristina Eisenberg, Moderator

Discussion Topic:

The Wolf's Tooth: Keystone Predators, Trophic Cascades, and Biodiversity]



In the early 1900s, while cruising timber as a young forester, American conservationist Aldo Leopold, founder of the science of wildlife biology, encountered a female wolf with her pups. The common wisdom of that era was that the only good predator was a dead one, so he and his crew opened fire. But as he stood there watching the “fierce green light” fade in the wolf mother’s eyes, he felt a sharp, surprising pang of remorse. It would take him decades to parse out his feelings about her death.

In 1935, Leopold bought an abandoned farm in southwestern Wisconsin as a hunting reserve. Today known as the Leopold Memorial Reserve, this land, which he and his family dubbed “the shack,” became the site of some of his deepest lessons about the ecological value of predators. In shack journals between 1939 and 1940, he noted that deer were nipping plants and trees down to eighteen inches in height. In a 1940s game survey, he found that humans had eliminated wolves throughout North America, causing an explosion in deer and elk numbers, and resulting degradation of forests through over-browsing. Meanwhile, back at the shack, deer calmly stood their ground in the absence of wolves, chronically browsing tender young saplings to death.

Near the end of his life, in possibly his most famous and poignant essay, “Thinking Like a Mountain,” Leopold reflected on his early encounter with that mother wolf and the wildlife management implications of her death: “While a buck pulled down by wolves can be replaced in two or three years, a range pulled down by too many deer may fail of replacement in as many decades.”



Today ecologists refer to the powerful ecological link between predators, their prey, and the foods prey eat as trophic cascades. We have learned much about the conservation value of keystone predators, which have the ability to touch everything in a food web, thereby creating healthy, resilient ecosystems. Now more than sixty years since Leopold’s death, we are actively restoring these predators to oceans, streams, forests, and prairies worldwide.

Trophic cascades are an ecosystem’s stories writ large upon terrestrial and aquatic landscapes. Please join me over the next month to explore some of the ecological stories I write about in The Wolf’s Tooth. Ecosystems speak to all of us—researchers, managers, students, and plain members of the biotic community—through the glyphs left by the interactions of keystone predators and their prey. These stories are part of the rubric of conservation and can inform an alternative to single-species conservation. And if we play close attention, they will tell us what to do as we strive for sustainability in our rapidly changing world.

Here are some questions to which you can respond via the "Comment" link below.

How do keystone predators structure ecosystems

What are some of the patterns in an ecosystem linked to trophic cascades?

In places where we can’t have keystone predators, do you think hunting by humans can be used to create similar effects?

British ecologist Charles Elton referred to the food web as an “integrated economy” in which members exchange energy. Beyond keystone predators, their prey, and the food prey eat, what other kinds of exchanges could be created by trophic cascades?

How have Elton’s and Leopold’s ideas about the ecological value of predators influenced wildlife management today?

10 comments:

Margaret said...

Stories speak to all of us and it is very cool to read about those ecological concepts in a story telling format. I like to look at all of this through your "biologist eye," a differrent way to look at what I have often thought of as the food web. Help me understand how trophic cascades differs from the basic food chain with which we are all familiar? I look forward to hearing more about your conservation career choices and what made you choose this field....

Cristina Eisenberg said...

Dear Margaret,

Trophic cascades are a food web's stories written on a landscape. As humans, we respond instinctive to stories, because of our prehistoric and current tradition as storytellers. I chose the field of conservation biology, and specifically work as a wolf biologist, because when wolves recolonized the place where we live in rural Montana I saw everything change in a matter of five years. These compelling ecological changes made me deeply curious about how wolves can restructure ecosystems. This inspired me to study these relationships as a scientist. In subsequent posts I will share more about what I saw happen on our land and what I am seeing in the other lansdcapes where I conduct research.

Len said...

Dear Christina,

As someone who works overseas in "development," I am eager to know how I might apply your experiences and wisdom to communities in which human-predator conflicts are the norm rather than the exception. Here in Afghanistan, wolves prey on sheep and goats in the central highlands, as do snow leopards in Badakhshan. Proof of the presence of Persian leopards is in the skins for sale in Kabul. What is not similar, though, is the absence of wild ungulates; undoubtedly these have been replaced by domesticated livestock, to the great detriment of rangelands. Altering mindsets here is more a matter of survival - for the predators as well as human households - than in the US.

Cristina Eisenberg said...

Dear Len,

You have brought up the crux of matter. We live in a world with a burgeoning human population in which we have made enormous modifications to ecosystems. You describe how in Afghanistan lack of wild ungulates has created a situation where wolves and other predators are prey-switching to domestic ungulates (sheep), which have significantly damaged rangelands. You are right, fundamentally the way to create healthier, more resilient ecosystems is by opening minds and changing the way people think about the natural world.

I work as the research director on a 192,000 acre working ranch in Colorado, The High Lonesome Ranch. My job there is to implement science that can help managers improve ecosystem health amid very active cattle ranching and hunting. That the owners believe predators benefit land health via trophic cascades is the first step.

Recently, Wildlands Network and the High Lonesome Ranch convened a meeting of the largest landowners in the American West. We had 8 million acres of privately owned land represented at this gathering. We thought the topics that would come up would be primarly about ranching economics. We were wrong. The top topic was how to conserve predators—specifically wolves, but also cougars and bears--and why it is important to do so. That so many large landowners in the rural West support predator conservation and understand trophic cascades is encouraging. But much work needs to be done with rural communities in this country and abroad to increase understanding and tolerance, but more importantly, to offer the support to make living with predators feasible. Issues such as depredation on livestock, which in America is not a huge problem, need to be addressed everywhere.

Jim Estes said...

The issues that Christina speaks to concerning wolves and trophic cascades apply as well to other species of large apex consumers and their ecosystems. This in turn has direct relevance to conservation planning on a global scale. The following is is a blog piece I wrote on this
latter point for the Defenders of Wildlife (see next comment):

Jim Estes said...

Large predators are critical to the stability of our natural areas

In a world containing some 10 million or more species, the current tide of extinction cannot be stemmed one species at a time. More general strategies are needed. Nearly everyone understands this fundamental truth. But what are these strategies? Although the devil is in the details, the answer in the minds of most conservation thinkers and planners hinges on a single key factor—habitat. All species require habitat to survive and reproduce. Preserve enough habitat in the right places and species preservation will follow. The problem is that this strategy isn’t working very well. We continue to lose species, even from the largest conservation areas. Why is that? It might be that the strategy is fine but we have yet to get the details right—i.e., enough habitat with sufficient protection in the right places. Or it might be that something more is needed.

On 13 July, 2011, I coauthored a review in the journal Sciencewith 23 other ecologists from around the world in which we argue that something more is indeed needed. That something is the apex consumers. Our argument is this: Large apex consumers--creatures like lions, wolves, bears and killer whales--are key elements of nature. Virtually all habitats have had them for millions of years. That is, until recently. These large apex consumers have been among the first species to disappear from our increasingly human-dominated world. And along with the loss of these animals has been the loss of something even more fundamental—the essential roles they play in holding their ecosystems together. We are beginning to see these roles nearly everywhere—from the tropics to the poles, and on land, in rivers and lakes, and in the sea. Our review details the theoretical basis for this phenomenon and provides many specific examples.

My favorite example is the link between sea otters and coastal ecosystems in the North Pacific Ocean. The loss of otters has led to population irruptions of their prey—sea urchins. Hyperabundant urchins overgraze kelp forests, leading in turn to reductions or the loss of species and ecosystem services that depend on kelp forests. Similarly, the loss of wolves, grizzly bears and cougars from much of North America has led to population irruptions of their prey—moose, elk and deer—which in turn have overgrazed their range, thus leading to the loss of both plant species and the animals that depend on these plants. In another well known example, the loss of coyotes from chaparral fragments in southern California has allowed these habitats to be invaded by “mesopredators”--cats, foxes, and other small carnivore--that in turn have caused the extinction of birds and other small vertebrates. The list goes on and on. These are not unique stories but examples of a global phenomenon. And the effects of apex consumers extend widely across ecosystems to influence such diverse phenomena as wildfire, disease, and air and water quality. Trophic downgrading, which begins with the loss of large apex consumers from nature, can be thought of as an ecological chain reaction that is part and parcel to the biodiversity crisis.

What does this mean to wildlife conservation? It means that while habitat is essential, by itself habitat conservation is not enough to conserve biodiversity. This in turn has several obvious implications for conservation planning. Small conservation areas are doomed to fail, or at least doomed to be much less than they might otherwise be because small areas are incapable of maintaining viable populations of large, apex consumers. Even large conservation areas are doomed to under-perform unless they also contain the apex consumers.

The bottom line for conservation is simply this. Habitat is necessary but insufficient for biodiversity conservation. Apex consumers are also required to run nature’s engine.

[from Defenders of Wildlife blog post by James Estes]

Cristina Eisenberg said...

You can read much more about the effects of trophic downgrading and the importance of apex predators in the book "Trophic Cascades: Predators, Prey, and the Changing Dynamics of Nature," edited by John Terborgh and Jim Estes, published by Island Press in 2010. Jim's book is filled with examples of the effects of trophic downgrading across many different types of ecosystems.

What I call the Field of Dreams Hypothesis, e.g., "If you build it they will come," is essentially about habitat. In our rapidly changing world, sadly, we are learning that if you build it they don't always come, because we have removed the apex predators that maintain habitat structure and function in ecosystems.

Len said...

Jim et al., It's of course not only predators that are in the class "apex consumers." John (Terborgh) or Patricia Wright could weigh in here, in regard to the role lemurs play in regenerating Madagascar's rainforests. For those of us without easy access to Island Press - what (if anything) do we know about the role of fossas in Madagascar? Jaguars in the Amazon? For that matter, the feline triumvirate on the African plains, where their role in natural selection (vs. trophic cascades) has been recognized for decades? What actually constitutes an "apex predator" on these plains, given the number of competing predator species? Closer to home, pumas in the American West? How have Tasmanian forests changed with the loss of the Tasmanian tiger? Is there, do you speculate, inevitably a connection between an apex predator and a trophic cascade?

WILD READ Team said...

More information about Terborgh and Estes book that Cristina references in earlier comment: Trophic Cascades: Predators, Prey, and the Changing Dynamics of Nature edited by John Terborgh and James Estes and published by Island Press (2010).

Cristina Eisenberg said...

Dear Len,

Wonderful questions. My response is likely yes to all. the effects of loss of apex or keystone predagtors is profound, rev erberates through every part of a food web. Jim at al.'s Science article (link provided in Jim's post) about trophic downgrading provides an elegant, comprehensive overview of these relationships on a global scale. Another good source besides the Terborgh and Estes trophic cascades book and my book, is Will Stotzenburg's book, "Where the Wild Things Were," which is written for a more general audience.