Some Animals Are More Equal than Others: Keystone Species and Trophic Cascades

Summary

The script narrates the pivotal experiments of ecologist Robert Paine, who discovered the concept of 'keystone species' and 'trophic cascades'. Paine's removal of a predator, the purple starfish, from a coastal ecosystem led to a dramatic decrease in species diversity, illustrating the starfish's key role. Further studies by Paine and James Estes on sea otters and their impact on kelp forests reinforced the top-down control predators exert on ecosystems. The script underscores the significance of apex predators in maintaining ecological balance.

Takeaways

• 🌿 The concept of 'green world hypothesis' suggests that predators play a crucial role in maintaining the health of ecosystems by controlling herbivore populations.
• 🔬 Robert Paine's experiment with starfish on the Pacific coast demonstrated the 'keystone species' concept, where the removal of a top predator can lead to a significant decrease in species diversity.
• 🌊 Paine's research showed that a single predator, like the starfish, can regulate the composition of an entire community, emphasizing the importance of predators in ecosystems.
• 🐙 The study of sea otters and their impact on kelp forests by James Estes revealed another example of a keystone species, where sea otters control sea urchin populations, which in turn affect kelp growth.
• 🐋 The decline in sea otter populations due to orca predation highlighted the 'trophic cascade' effect, where the removal or addition of a species at one trophic level can have cascading effects on other levels.
• 🌳 The script underscores the importance of understanding the role of apex predators in maintaining biodiversity and the structure of ecosystems.
• 🌍 The concept of 'top-down forcing' in ecology, introduced by Paine's work, shifted the focus from a purely bottom-up view of ecosystems to one that considers the impact of predators at the top of the food chain.
• 🐳 The script illustrates how human activities, such as whaling, can indirectly affect ecosystems by altering predator-prey dynamics and leading to unforeseen consequences.
• 🔍 The research discussed in the script has practical implications for conservation efforts, emphasizing the need to consider the role of keystone species and trophic cascades in ecosystem management.
• 🌱 The story of Paine's and Estes' work serves as a reminder of the interconnectedness of ecological communities and the potential for human actions to have far-reaching effects on the natural world.

Q & A

What was the significance of Robert Paine's experiment with starfish on the rocky Pacific shore in 1963?

Robert Paine's experiment was significant because it marked one of the most important experiments in the history of ecology, demonstrating the concept of a 'keystone species' and its impact on the ecosystem. By removing starfish, Paine observed the rapid change in the community structure, leading to a decrease in species diversity.

What is the 'green world hypothesis' mentioned in the script?

The 'green world hypothesis' is a concept that suggests the world is green because predators keep herbivores in check, thus preventing them from consuming all the plant life. This hypothesis was radical at the time as it proposed that predators play a crucial role in regulating ecosystems.

How did the removal of starfish by Robert Paine affect the number of species in the rock community?

The removal of starfish led to a decrease in the number of species in the rock community. Initially, the number of species decreased from 15 to eight, and after seven years, it further simplified to a monoculture dominated by mussels, showing the starfish's role as a keystone species in maintaining biodiversity.

What is a 'keystone species' and how did Paine's experiment help define this term?

A 'keystone species' is a species that has a disproportionately large effect on its environment relative to its abundance. Paine's experiment helped define this term by showing that the removal of a single predator, the starfish, could drastically alter the entire community structure and lead to a significant decrease in species diversity.

What is a 'trophic cascade' and how was it demonstrated in the script?

A 'trophic cascade' refers to the indirect effects that a predator can have on an ecosystem by controlling the distribution of resources and influencing the populations of other species. In the script, it was demonstrated through the example of sea otters controlling sea urchins, which in turn affect kelp populations.

How did the fur trade impact the ecosystem as described in the script?

The fur trade led to the near extinction of sea otters, which resulted in an increase in sea urchin populations as there were no longer any predators to control them. This caused a decrease in kelp, demonstrating the top-down impact of predator removal on the ecosystem.

What role did sea otters play in the coastal ecosystem according to James Estes' research?

Sea otters played a key role in the coastal ecosystem by controlling the population of sea urchins, which in turn affected the abundance of kelp. The presence of sea otters maintained the balance of the kelp forest, which is crucial for many coastal species.

Why did the orcas start eating sea otters according to the script?

The orcas started eating sea otters because their primary prey, whales, had been significantly reduced due to whaling activities. This forced the orcas to broaden their diet and start feeding on other species, including sea otters.

How did the decline in whale populations affect the coastal ecosystem?

The decline in whale populations due to whaling activities led to a trophic cascade effect. With fewer whales, orcas began preying on sea otters, which in turn caused an increase in sea urchin populations and a decrease in kelp, illustrating the far-reaching impacts of human activities on ecosystems.

What is the importance of understanding the role of apex predators in ecosystems as emphasized by Robert Paine?

Understanding the role of apex predators is crucial because they can have significant top-down effects on ecosystems. Ignoring this can lead to ecological imbalances and mistakes in conservation efforts. Apex predators help maintain biodiversity and the overall health of the ecosystem.

Outlines

00:00

🌿 The Birth of the Green World Hypothesis

The script begins with a discussion on the diversity of Earth's habitats and the factors influencing species populations. It recounts Robert Paine's pivotal 1963 experiment on the Pacific coast, which marked a significant moment in ecology. The narrative then shifts to a classroom at the University of Michigan, where Professor Fred Smith posed a thought-provoking question about the greenery of a tree, leading to a discussion on food chains. The script introduces the concept of the 'green world hypothesis,' which suggests that predators play a crucial role in maintaining the balance of ecosystems by controlling herbivore populations, thus preventing them from over-consuming plant life.

05:09

🌊 Paine's Experiment and the Keystone Species

This section delves into Robert Paine's fieldwork on the rocky shores of the Pacific, where he meticulously studied the interrelationships among various marine species. Paine identified the large purple starfish, Pisaster ochraceus, as a top predator and proceeded to remove it from certain areas to observe the consequences. His findings revealed that the absence of this predator led to a dramatic decrease in species diversity, as mussels began to dominate the ecosystem. Paine coined the term 'keystone species' to describe the outsized influence such predators have on their environments, emphasizing that not all species impact their ecosystems equally.

10:11

🐾 Trophic Cascades and the Role of Sea Otters

The script then explores the concept of 'trophic cascades,' where the removal or presence of a species can have a ripple effect on an ecosystem. It introduces James Estes, who collaborated with Paine to study the impact of sea otters on kelp forests. Estes discovered that in areas where sea otters were absent, sea urchin populations thrived, leading to the decimation of kelp. This finding underscored the green world hypothesis and demonstrated how predators like sea otters are essential for maintaining the health and diversity of coastal ecosystems.

15:13

🐋 The Impact of Killer Whales on the Ecosystem

In the final section, the script discusses how human activities, such as whaling, can indirectly affect ecosystems through a process known as trophic cascades. It details how the depletion of whale populations forced killer whales to expand their diet to include sea otters, which in turn led to an increase in sea urchin populations and the subsequent collapse of kelp forests. This chain of events illustrates the interconnectedness of ecosystems and the far-reaching consequences of human actions on biodiversity. The script concludes by emphasizing the importance of understanding and conserving top predators for the health of ecosystems.

Keywords

💡Ecology

Ecology is the scientific study of the interactions among organisms and their environment. In the video, ecology is central to understanding how different species interact within their habitats and how these interactions shape the overall health and diversity of ecosystems. The video explores the concept of keystone species and trophic cascades, illustrating how the removal or presence of certain species can have profound effects on the entire ecosystem.

💡Habitat

A habitat refers to the natural environment in which an organism or group of organisms live. The video script mentions various habitats such as jungles, deserts, and seashores, emphasizing the diversity of ecosystems on Earth. Each habitat supports a unique community of plants and animals, highlighting the importance of preserving these environments for biodiversity.

💡Species

Species are groups of living organisms that can interbreed and produce fertile offspring. The video discusses the variety of species present in different habitats and how their populations are regulated. It also touches on the concept of keystone species, which are species that have a disproportionately large effect on their environment relative to their abundance.

💡Population

A population is all the individuals of the same species living in a particular area. The video script discusses how the number of species and the size of populations are determined by various ecological factors. It also explores how the removal of predators can lead to an increase in certain populations, such as that of sea urchins, which can then have cascading effects on the ecosystem.

💡Food Chain

A food chain is a linear network of links in an ecosystem starting from producer organisms (green plants) and ending at predator species, decomposed by decomposer organisms. The video script discusses the idea that the number of producers limits the number of herbivores, which in turn limits the number of predators, illustrating the top-down and bottom-up regulation of ecosystems.

💡Green World Hypothesis

The Green World Hypothesis suggests that the world is green because predators keep herbivores in check, thus preventing them from over-consuming plant life. The video script recounts how this hypothesis was tested and confirmed through experiments, showing that predators play a crucial role in maintaining the balance of ecosystems.

💡Trophic Cascade

A trophic cascade is a phenomenon where changes at one trophic level (or step in the food chain) create ripple effects through the entire ecosystem. The video script provides examples of trophic cascades, such as when the removal of sea otters leads to an increase in sea urchin populations, which in turn results in the decline of kelp forests.

💡Keystone Species

A keystone species is a species that has a disproportionately large effect on its environment relative to its abundance. The video script introduces the concept through the example of the starfish, which, despite not being a large or numerous species, plays a critical role in maintaining the diversity of its ecosystem by controlling mussel populations.

💡Robert Paine

Robert Paine was an American marine biologist and a pioneer in the study of ecological communities, particularly in the field of keystone species. The video script describes his influential experiments on the Pacific coast, which helped to establish the concept of keystone species and their role in ecosystems.

💡James Estes

James Estes is a prominent marine ecologist known for his work on the role of sea otters in kelp forest ecosystems. The video script details his research, which demonstrated how the decline of sea otter populations due to killer whales led to a significant increase in sea urchins and the subsequent collapse of kelp forests.

💡Biodiversity

Biodiversity refers to the variety of life in an area and the variability within and between species. The video script underscores the importance of biodiversity by showing how the presence or absence of keystone species can lead to significant changes in the number and variety of other species in an ecosystem.

Highlights

Robert Paine's experiment with starfish on the Pacific shore in 1963 marked a pivotal moment in ecology, challenging existing theories on species population and community structure.

The 'green world hypothesis' proposed by Fred Smith, Nelson Hairston, and Lawrence Slobodkin suggested that predators play a crucial role in ecosystem regulation, contrary to the prevailing bottom-up theory.

Paine's removal of starfish from rocky outcrops led to a decrease in species diversity, demonstrating the 'keystone species' concept where a single predator can significantly influence an ecosystem.

The term 'keystone species' was coined by Paine to describe species that have a disproportionately large effect on their environment relative to their abundance.

James Estes' encounter with sea otters and their impact on kelp forests provided further evidence for the 'green world hypothesis' and the concept of trophic cascades.

The decline in sea otter populations due to killer whales, a result of over-hunting of whales, exemplified how human activities can indirectly cause trophic cascades in ecosystems.

Estes' research showed that the removal of sea otters led to an increase in sea urchin populations and a subsequent decline in kelp, highlighting the interconnectedness of ecological communities.

The concept of trophic cascades, where changes at one level of a food chain affect all other levels, has been instrumental in shaping modern ecological understanding.

Paine's work underscored the importance of predators in maintaining biodiversity and the balance of ecosystems, a perspective that has influenced conservation strategies.

The study of keystone species and their effects has led to a paradigm shift in ecology, moving from a bottom-up to a top-down perspective on ecosystem regulation.

The Aleutian Islands provided a natural experiment site for studying the effects of sea otters on kelp forests, illustrating the power of predators in shaping coastal ecosystems.

The decline in whale populations due to whaling activities had unforeseen consequences on coastal ecosystems, demonstrating the far-reaching impacts of human actions on nature.

Estes' discovery that killer whales were preying on sea otters, a response to the depletion of their traditional food sources, underscored the dynamic and adaptive nature of predator-prey relationships.

The study of trophic cascades has provided valuable insights for conservation efforts, emphasizing the need to consider the role of apex predators in ecosystem health.

The recognition of top-down effects in ecosystems has been crucial for understanding and managing biodiversity, a lesson underscored by the work of Paine and Estes.

The transcript highlights the importance of long-term ecological research in uncovering the complex relationships and dynamics within ecosystems.

Transcripts

[MUSIC PLAYING]

SEAN CARROLL: From jungle to desert, from forest

to PLANE from mountaintops to the seashore,

the Earth is home to many habitats.

And every habitat contains a community of plants and animals

each community is populated by different species.

And each species is present in different numbers.

So what determines how many species live in a given place,

or how large each population can grow?

The answers to such basic questions

about how nature works eluded biologists for a long time,

until, on this rocky Pacific shore in 1963,

young zoology professor Robert Paine

pried a purple starfish off the rocks

and threw it out into the bay.

And so began one of the most important experiments

in the history of ecology.

[MUSIC PLAYING]

So what brought Robert Paine to this rugged coast?

And why was he hurling starfish?

The answer takes us back a few years to a classroom

at the University of Michigan.

ROBERT PAINE: It was a lovely day.

The old zoology building at Ann Arbor had a courtyard.

And in that courtyard, there was a tree

which was beginning to bud out.

SEAN CARROLL: Professor Fred Smith

asked his students a seemingly simple question.

ROBERT PAINE: And he said, class,

I want you to think about this.

Why is that tree green?

And someone said--

SPEAKER: Chlorophyll.

ROBERT PAINE: Fred said, what keeps the leaves there?

SEAN CARROLL: Although technically, chlorophyll

is what makes trees green, Fred Smith

was asking a bigger question.

He was thinking about food chains.

ROBERT PAINE: You obviously had producers.

They are the energy suppliers to whatever lives off of them.

You have consumers on top of that.

And we know the herbivores.

SEAN CARROLL: The popular idea at the time

was that the number of producers limits

the number of herbivores.

In turn, the number of herbivores

limits the number of predators that feed on them.

Every level was regulated by the amount of food

from the bottom of the food chain going up.

But this view didn't explain why herbivore populations don't

simply grow to the point where they eat

all of the leaves on the tree.

Professor Smith had discussed this conundrum

with two colleagues, Nelson Hairston and Lawrence Slobodkin

They proposed a new idea.

The number of herbivores must be controlled

not only from the bottom up, but also from the top down.

ROBERT PAINE: The herbivores had the capacity of destroying

the plant community.

Trees could be defoliated.

And why weren't they defoliated?

And the answer was because there weren't enough insects around

to do that.

And that was the role of predators.

SEAN CARROLL: The world is green because predators

keep herbivores in check.

This was a radical concept that became known as the green world

hypothesis.

Up until that time, no one thought

predators had any role in regulating ecosystems.

ROBERT PAINE: This class was the first public vetting

of the green world hypothesis.

SEAN CARROLL: And one of Smith's students, Robert Paine,

would be the one to put this idea to the test.

A few years later, as a new professor

at the University of Washington, Paine

went looking for a system where he could

study the role of predators.

ROBERT PAINE: I discovered the Pacific Ocean

and this magnificent array of organisms

which lives along its margins.

There it was, spread out in front of me.

It was nirvana.

SEAN CARROLL: He began by identifying all the organisms.

And then he started mapping out who eats whom.

ROBERT PAINE: There were carnivorous gastropods

feeding on barnacles.

There were sea urchins feeding on algae.

There was a lot of pattern.

SEAN CARROLL: His observation showed

that a species of large purple and orange starfish

called pisaster ochraceus was at the top of the food chain.

Starfish may seem like unlikely predators,

but speed time up a bit, and you'll see deadly hunters.

ROBERT PAINE: If a starfish is feeding, you turn it over

and you see what the starfish is eating.

They're eating mussels.

They're eating a lot of other things as well,

but they're eating mussels.

SEAN CARROLL: So Paine asked, what

happens when you remove the predator

starfish from a single outcrop?

ROBERT PAINE: You have to surprise them.

Because a starfish clamps down.

It takes a strong wrist and a pry bar.

I would then scale them as far as I could.

And in those days I could throw a starfish 60 or 70 feet out

to deeper water.

There were always starfish marching in.

So during the summer months, I would drive the 350-mile round

trip, hit the area at low tide, do my removal, take other data,

and then return to Seattle.

SEAN CARROLL: The ecosystem started to change rapidly.

ROBERT PAINE: Within a year and a half,

I knew that I had ecological gold.

SEAN CARROLL: Although the top predator

had been removed, surprisingly, the number

of species in the rock actually decreased from 15 to eight.

ROBERT PAINE: After three years, I think it went down to seven.

But then by seven years, it simplified itself.

It was basically a monoculture.

I had changed the nature of the system.

SEAN CARROLL: As the experiment continued, the line of mussels

advanced down the rock face, monopolizing almost all

of the available space and pushing all other species out.

Paine had discovered that one predator

could regulate the composition of an entire community.

He coined a term to describe the power a single species can

exert on an ecosystem.

ROBERT PAINE: I know very little about architecture.

If you build an arch, you have to get the two sides of it

to put pressure against one other.

And therefore, at the apex of the arch, you have a keystone.

You pull the keystone out, and the structure collapses.

SEAN CARROLL: Many predators, like pisaster starfish,

turn out to be keystone species.

ROBERT PAINE: These keystone species

have a huge impact, which extends

well beyond to the species they primarily prey on.

SEAN CARROLL: Most species do not have large impacts.

In other experiments, Paine had removed various species.

But that had little or no effect on the ecosystem as a whole.

ROBERT PAINE: All animals are equal,

but some animals are more equal than others.

And that expresses the fact that all species don't

have the same impact on the system they're in.

It takes experiments to tease that out.

And that's often not easily done.

SEAN CARROLL: Paine's pioneering experiments

and the concept of keystone species

sent ripples through the field of ecology

and turned thinking about the regulation of communities

upside down.

ROBERT PAINE: Remove the predator,

the system simplifies itself.

This is an ecological concept which is general and global.

SEAN CARROLL: As Paine continued his studies

a little further from shore, he noticed

another striking pattern.

ROBERT PAINE: There were a lot of tide pools.

And some of the tide pools were dominated by urchins.

Some weren't.

SEAN CARROLL: In the tide pools with lots of urchins,

there was much less kelp.

Paine suspected the urchins were keeping the kelp from growing.

ROBERT PAINE: And I said to myself, that's

my next round of experiments.

SEAN CARROLL: Paine removed all the urchins by hand

from some pools, and left nearby pools untouched.

Again, the results were dramatic.

In the pools where he removed urchins,

the kelp started growing almost immediately.

ROBERT PAINE: Urchins control the kelp.

Therefore, this is a total violation

of the green world hypothesis.

SEAN CARROLL: The urchins in Paine's pools

were eating all of the kelp.

So why was nothing regulating the urchin populations?

The answer would come from a fortuitous

meeting on a remote island in Alaska's Aleutian Island chain.

There, Paine would cross paths with another scientist.

In 1971, James Estes was an ambitious young graduate

student.

JAMES ESTES: At the time that Bob and I met,

I was just beginning to try to think my way through what

it was I was going to do.

ROBERT PAINE: We met in a bar after a movie.

I was just in sea urchins.

And Jim, I think, was doing a study on sea otter physiology.

JAMES ESTES: I was explaining to him

what it was that I was thinking of trying to do,

which was somehow understand how an ecosystem

like the one in Amchitka Island could

support such a high abundance of predators

and do that through an understanding of production

and efficiency of energy and material flow

upward through the food web.

And Bob's explicit or implicit reaction to that

was, that's just not very interesting,

and, have you ever thought about what these animals might

be doing to the system?

SEAN CARROLL: Paine realized if Estes focused

on what sea otters were doing from the top

down rather than the kelp from the bottom up,

he might discover the role otters play

in the organization of nature.

JAMES ESTES: And so I thought, why not?

Let's go out and have a look.

SEAN CARROLL: Paine was suggesting

an approach similar to his starfish throwing experiment--

remove otters from the ecosystem and test the impact

that had on other species.

JAMES ESTES: But I don't think, at that time,

that Bob had any perception of how that might be done.

But I did, because I knew quite a bit

about the history of the otter.

They were abundant across the North Pacific.

And then the Pacific Maritime fur trade began in 1741.

And over the subsequent 150 years,

otters were hunted to the brink of extinction.

In 1911 or 1912, fur take was prohibited.

And a few of those colony survived and served as a seed

for the recovery of the species.

SEAN CARROLL: But the sea otter recovery was spotty.

JAMES ESTES: They had completely recovered

from the fur trade at a number of island systems

across the Aleutian archipelago, of which Amchitka is a part.

There were other island systems where they had not yet

recovered.

SEAN CARROLL: The experiment was simple--

compare ecosystems with otters to those without.

He began with his home island of Amchitka.

JAMES ESTES: I knew a lot about what Amchitka looked like.

I knew that sea urchins were common, but very small.

SEAN CARROLL: The next step was to arrange

for a dive at nearby Shemya Island,

a location with no otters.

JAMES ESTES: The most dramatic moment

of learning in my life happened in less than a second.

And that was sticking my head in the water at Shemya Island.

It was just green with urchins and no kelp.

And it all sort of fell into place in just an instant,

that the loss of otters from that system

had completely reorganized that system from which

kelps had probably been very abundant before the loss

of otters to one in which the sea urchins now had become

abundant in the absence of the otters

and had eaten all the kelps.

SEAN CARROLL: It was a striking demonstration

of the green world hypothesis.

Sea otters, the predators, were controlling the urchins

that fed on the kelp.

Remove the sea otters, and the kelp forests disappear.

Paine called these cascading effects

of one species downward upon others trophic cascades.

ROBERT PAINE: Trophic cascade is when

you have an apex predator controlling

the distribution of resources, and they

lead to these cascades of indirect effects--

lots and lots of indirect effects.

You have fewer sea otters.

You have more sea urchins.

You have fewer kelp.

JAMES ESTES: I expect every coastal species is probably

impacted in one way or another by the presence

or absence of kelp.

Kelp forest fishes depend a lot on kelp.

There are birds that feed in the kelp forests.

There are invertebrates that feed in the kelp forest.

Virtually everything that lives in the coastal zone

depends upon that system in some way.

SEAN CARROLL: So sea otters are another keystone species.

They regulate the structure of this coastal marine community.

ROBERT PAINE: The results are unambiguous.

Sea otters drive the system from the top down.

So the message is clear, and it's

been enormously important in how ecologists

tend to view the world.

SEAN CARROLL: Estes returned regularly to Alaska

to study otters.

Some 20 years later, he noticed something strange

was happening.

JAMES ESTES: We were capturing otters,

having a devil of a time catching enough.

And that was peculiar, because I'd never

had trouble catching otters.

SEAN CARROLL: Otter populations seemed to be declining.

He tried to think of every possible explanation.

JAMES ESTES: And we essentially lined up all of the hypotheses

that we could think of that could be causing

this population decline.

SEAN CARROLL: He ruled out starvation.

He ruled out disease.

And then a third hypothesis emerged.

JAMES ESTES: Tim Tinker, who is a technician,

called me one day in the winter and said,

you know, I'm starting to wonder if it might be killer whales.

And I said, you're crazy.

I mean, this just couldn't happen.

They don't eat otters.

He said, yes, they do.

I've seen them eat a couple.

SEAN CARROLL: But how could he test it?

Once again, nature provided an ideal site.

JAMES ESTES: We went into a place called Clam Lagoon.

It provided us a site that orcas could not get to.

We had no problem catching about 30 animals in two or three

days.

And the fact that that little population did not

decline when everything else did the orcas had access to

helped me become convinced that it was a viable hypothesis.

SEAN CARROLL: Why were the orcas now eating otters?

Orcas generally eat whales, not otters.

JAMES ESTES: There were a lot of whales

around after World War II.

After World War II, the Japanese and the Russians

started reducing those whales.

And by the late 1960s, they had been depleted by 90%.

And the full stripping of all these big whales

out of the system shocked these killer whales and forced

them to broaden their diet and start

feeding on these other species.

What had happened is that we had taken

this three-level trophic cascade,

and the orcas had added a fourth trophic level,

and it made that system behave just like the theory predicted.

SEAN CARROLL: With the orcas eating otters,

urchin populations increased, and kelp disappeared.

JAMES ESTES: To me, the amazing part of that

was the notion that something like whaling, that

started in the middle of the 20th century way

out in the oceanic realm of the North Pacific,

could affect something like urchins and kelp

and the coastal ecosystem.

It was mind-boggling to even conceive of something.

It was almost like science fiction.

SEAN CARROLL: To Robert Paine, this

was a satisfying confirmation.

ROBERT PAINE: And it provided an example

of how the concept of a trophic cascade functions in nature.

And it's Jim's work in the Aleutians

which in fact solved the case.

SEAN CARROLL: As ecologists explored other habitats

with new eyes, they discovered keystone species

and trophic cascades in many places.

And just as with otters, the removal

of predators such as wolves, sharks, and lions

has had profound effects on the number

and variety of other species and on ecosystems as a whole.

These fundamental insights have changed

the way we look at the world, and they've

given ecologists and conservationists

a new set of tools.

JAMES ESTES: It has turned us from a fundamental view

of nature that was bottom-up.

More than any other single ecologist,

he was the one that transitioned our thinking to the importance

of top-down forcing.

ROBERT PAINE: Oh, thank you.

JAMES ESTES: No, it's the truth.

SEAN CARROLL: But from Paine's vantage point,

humans still have much to learn.

ROBERT PAINE: To ignore the fact that there are top down effects

is to invite mistakes.

One ignores at one's own risk what role apex predators play.

[HOWLING]