Community Ecology: Feel the Love - Crash Course Ecology #4

Summary

This episode of Crash Course: Ecology delves into the competitive nature of life, exploring how species interact through competition for limited resources, a concept central to community ecology. It introduces the Competitive Exclusion Principle, ecological niches, and how species adapt to avoid direct competition, leading to resource partitioning and character displacement. The video also touches on mutualism and commensalism as alternative strategies for survival, hinting at the dramatic world of predation in the next episode.

Takeaways

• 🌿 Life is inherently competitive due to limited resources and the drive to survive and reproduce.
• 🔬 Biology is fundamentally about sex and avoiding death, which are complicated by competition among species.
• 🌳 Community ecology examines interactions between species that define ecological communities, from small habitats to vast ecosystems.
• 🦈 Competition is not always bloody; it often involves finding ways for species to coexist by dividing resources.
• 🧬 The Competitive Exclusion Principle, first identified by G. F. Gause, states that two species competing for the same resources cannot coexist indefinitely.
• 🌱 Species can avoid competitive exclusion by adapting to different ecological niches, which include both biotic and abiotic resources.
• 🏆 Ecological niches are like jobs in a community, providing species with a lifestyle based on the resources they secure.
• 🔑 The concept of 'fundamental niche' versus 'realized niche' illustrates the difference between an ideal situation and the actual role a species plays due to competition.
• 🔍 Robert MacArthur's research on warblers showed how species can partition resources and coexist without direct competition, a phenomenon known as resource partitioning.
• 📊 Character displacement is a result of natural selection favoring traits that minimize competition and increase survival chances.
• 🤝 Interspecies interactions aren't just competitive; mutualism and commensalism are examples of cooperative relationships that benefit species in different ways.

Q & A

What is the primary focus of the script's discussion on biology?

The script primarily discusses how competition for resources and the avoidance of direct competition shape the interactions between species in ecological communities.

Why is competition a significant factor in the interactions between species?

Competition is significant because there is a finite amount of resources on the planet, and evolution drives species to compete for these resources to ensure survival and reproduction.

What is the Competitive Exclusion Principle?

The Competitive Exclusion Principle, first identified by G. F. Gause, states that when two species are competing for the same resources, one of them will eventually outcompete the other, leading to the inferior competitor's elimination.

How did G. F. Gause demonstrate the Competitive Exclusion Principle in his experiments?

Gause demonstrated the principle by growing two species of protists, Paramecium aurelia and Paramecium caudatum, separately and together. When grown together, P. caudatum was driven to extinction by P. aurelia due to the latter's faster population growth.

What is an ecological niche, and why is it important for species survival?

An ecological niche is the sum of all resources, both biotic and abiotic, that a species uses in its environment. It is important for species survival because finding a niche allows a species to avoid competitive exclusion and secure a steady supply of resources.

What is the difference between a fundamental niche and a realized niche?

A fundamental niche represents the ideal situation where a species can live without competition, while a realized niche is the actual role and lifestyle a species adopts due to the need to avoid competition and survive.

What is resource partitioning, and how does it relate to the coexistence of similar species?

Resource partitioning is the phenomenon where similar species settle into separate niches, allowing them to coexist by dividing their use of limiting resources and minimizing direct competition.

Who was Robert MacArthur, and what was his contribution to community ecology?

Robert MacArthur was a Canadian-born ecologist known for his discovery of resource partitioning. He demonstrated that different species of warblers partitioned their resources by foraging, nesting, and breeding in different parts of trees, thus avoiding competition.

What is character displacement, and how did Peter and Rosemary Grant observe it in action?

Character displacement is a process where traits associated with minimizing competition are selected favorably. The Grants observed this in Galapagos finches, where smaller finches' beaks shrunk to specialize in eating smaller seeds, allowing them to coexist with larger finches that ate larger seeds.

What are mutualism and commensalism, and how do they represent conflict avoidance in interspecies interactions?

Mutualism is an interspecies interaction where both species benefit, such as in mycorrhizae relationships. Commensalism involves one species benefiting while the other is unaffected. Both represent conflict avoidance by creating relationships that are beneficial without competition.

Outlines

00:00

🌿 The Dynamics of Competition in Ecology

This paragraph introduces the concept of competition in ecology, emphasizing its role in shaping ecological communities. It explains that the finite nature of resources leads to competition among species, which is a driving force of evolution. The paragraph also touches on the idea that while competition is common, many species find ways to coexist by avoiding direct competition and dividing resources. The Competitive Exclusion Principle, introduced by G. F. Gause, is highlighted as a key principle in community ecology, stating that two species competing for the same resources cannot coexist indefinitely. The concept of ecological niches is introduced as a strategy for species to avoid competition and maintain a stable ecological community.

05:00

🕵️‍♂️ The Pioneering Work of Robert MacArthur

This section delves into the contributions of Robert MacArthur to the field of ecology, particularly his work on the niche differentiation of warbler species. MacArthur's research challenged the notion that similar species cannot coexist by demonstrating how five species of warblers partitioned resources in their environment. His detailed study of the birds' foraging, nesting, and mating habits revealed that each species utilized different parts of the trees and had unique behaviors, thus avoiding competition. This phenomenon, known as resource partitioning, is a key concept in understanding how species coexist and is a testament to MacArthur's influence on modern ecology.

10:02

🤝 The Cooperative Side of Interspecies Interactions

The final paragraph explores cooperative interactions between species, such as mutualism and commensalism, which are strategies to avoid competition. Mutualism is highlighted through examples like mycorrhizae and flowering plants attracting pollinators, where both parties benefit from the relationship. Commensalism is introduced with the example of barnacles on gray whales, where one species benefits without significantly affecting the other. The paragraph also mentions the potential complexities of these interactions, suggesting that what seems neutral may actually confer some advantage or disadvantage. The section ends with a teaser for the next episode on predation and its role in shaping ecological diversity.

Keywords

💡Competition

Competition in the context of the video refers to the struggle between organisms for the same resources, which is a driving force of evolution. It is central to the theme as it explains how species interact and adapt to survive in a world with finite resources. For example, the script mentions 'inter-species interaction is mostly competitive' and discusses the concept of competitive exclusion.

💡Ecological Communities

Ecological communities are groups of interacting species living in the same area. The video emphasizes that these communities are defined by the interactions between species, which can be competitive or cooperative. The script uses the term to describe the broader context in which species find their niches and interact.

💡Resource Partitioning

Resource partitioning is the concept where similar species divide resources to reduce competition, allowing them to coexist. The video explains this as a key mechanism in community ecology, using the example of different species of warblers utilizing different parts of trees to avoid direct competition.

💡Competitive Exclusion Principle

The Competitive Exclusion Principle, introduced by ecologist G. F. Gause, states that two species competing for the same resources cannot coexist indefinitely; one will eventually outcompete the other. The video uses this principle to illustrate the harsh realities of competition in nature and its implications for species survival.

💡Ecological Niche

An ecological niche is the role a species plays in its environment, defined by the sum of resources it uses. The video explains that finding a niche allows species to avoid competition and survive, using the metaphor of jobs in a community to illustrate how a species' lifestyle is determined by its niche.

💡Fundamental Niche

The fundamental niche represents the ideal set of resources and conditions a species would have if no competitors existed. The video contrasts this with the realized niche, which is the actual niche a species occupies due to competitive pressures, suggesting a trade-off between the ideal and the achievable.

💡Realized Niche

A realized niche is the niche a species actually occupies due to competition and other environmental pressures. The video explains that species may have to settle for a realized niche that is less than ideal to avoid competitive exclusion, as seen in the example of the warblers partitioning resources.

💡Character Displacement

Character displacement is the evolutionary process where traits of species diverge to reduce competition. The video describes this with the example of finches on Daphne Major, where the beak size of one species changed to specialize in different seeds, reducing competition with another species.

💡Mutualism

Mutualism is a type of interspecies interaction where both species benefit. The video provides examples such as mycorrhizae and flowering plants with pollinators, illustrating how mutualistic relationships can evolve to avoid competition and enhance survival.

💡Commensalism

Commensalism is an interaction where one species benefits while the other is unaffected. The video uses the example of barnacles on gray whales to explain this concept, suggesting that while the barnacles benefit, the whales are indifferent to their presence.

Highlights

Life is inherently tough and competitive due to limited resources, driving evolution for survival and gene spreading.

Competition is a key factor in species interaction and the formation of ecological communities.

Community ecology studies interactions from micro to macro scales, such as tide pools and oceans.

Inter-species interactions often involve avoiding direct competition to coexist peacefully.

Competitive exclusion is a fundamental ecological principle where one species outcompetes another for the same resources.

The Competitive Exclusion Principle was first identified by G. F. Gause through experiments with protists.

Not all resources are limiting, allowing for the coexistence of similar species in vast environments like oceans.

Species adapt to find ecological niches to survive competition, influencing their lifestyle and population growth.

An ecological niche is the sum of resources a species uses, defining its role and lifestyle in the community.

Competitive exclusion can be avoided by finding a unique niche, leading to a stable ecological community.

The fundamental niche represents an ideal situation where a species has no competition, rarely achieved in nature.

The realized niche is the actual ecological role a species plays due to competition and adaptation.

Robert MacArthur's research on warblers demonstrated resource partitioning, allowing similar species to coexist.

MacArthur's work emphasized the importance of niche differentiation in community ecology.

Character displacement is a natural selection process where traits evolve to minimize competition.

The Grants' study of Galapagos finches showed character displacement in response to competition for resources.

Mutualism and commensalism are forms of interspecies interaction that avoid competition through cooperation.

Mutualistic relationships, like mycorrhizae, benefit both parties involved, exemplifying successful cooperation in nature.

Commensalism is a relationship where one species benefits without affecting the other, like barnacles on whales.

Upcoming episodes will explore the world of animal predation and its impact on ecological diversity.

Transcripts

I wouldn't be much of a teacher if I didn't tell you that life is tough and that everyone's looking out for themselves in this world.

That's just the way it is, people.

You know how I always say that biology is ultimately about sex and not dying?

Well both of those things are more difficult than we'd like them to be, because of competition.

There's a finite amount of resources on this planet, so evolution drives us to compete for them

so that we can survive long enough to spread our genes all over the place

And naturally, competition is a really important part of how different species interact when their habitats overlap.

These interactions between species are what define ecological communities.

So it makes sense that community ecology studies these interactions anywhere they take place,

from a tide pool to the whole ocean, from a rotting log to an entire forest.

But just because inter-species interaction is mostly competitive doesn't necessarily

mean that community ecology is all about big, bloody, tooth-and-claw scenes like from cable-TV nature shows.

Actually, a lot of it is, but we're not going to get there until next week.

For now, let's just note that competition, while prevalent and important,

is also pretty dangerous, kind of a hassle, and can, like, really hurt.

So a lot of inter-species interaction is actually about sidestepping direct competition

and instead finding ways to divvy up resources, or otherwise let species just get along.

Can you feel the love?

[Theme Music]

Careful guys! Because right now we're surrounded potentially lethal interspecific competition going on all over the place.

Since we're animals, we usually think of competition as going on between animals,

but really it happens between almost all members of the four kingdoms of life.

Whenever species compete, they're going after the same resources that they need for their

survival and continued population growth.

In this garden, the weeds are competing with the sunflower, the corn and the dill for nutrients and water in the soil.

So these resources, because they're finite in this area, are the limiting factors that we've talked about.

The population can only get as big as these factors will allow.

Now, a particularly nasty weed could, over time, eliminate the veggies entirely.

Such elimination is known as competitive exclusion,

and it's one of the most fundamental properties in community ecology, and also, like, life.

Because the fact is, when two species are competing for the same resources,

one of them is eventually going to be more successful and eliminate the other.

This bitter truth is known as the Competitive Exclusion Principle,

and it was first identified in 1934 by Russian ecologist G. F. Gause

in a study of two closely-related species of microscopic protists.

When he was only 22 years old, Gause made a name for himself by conducting experiments

that pitted one species of protist, Paramecium aurelia, against another, Paramecium caudatum.

First, Gause grew each species separately with the exact same resources,

and found that each developed rapidly and established stable populations.

But, when he grew them in the same container, P. caudatum was soon driven to extinction by P. aurelia.

Paramecium aurelia gained a competitive advantage because its population grew slightly faster than P. caudatum's.

So Gause's experiment showed that, in the absence of another disturbance,

two species that require the same resources cannot live indefinitely in the same habitat.

The inferior competitor will be eliminated.

Makes sense, but if competitive exclusion is the natural law of the land,

then why isn't all of earth just a crazy crap-circus of constant competition, predation, and ultimately,

extinction of all those losers?

Well, for a couple of reasons: first, not all resources are limiting.

Two species of sharks may compete for water in the ocean, but the ocean is, you know, gigantic.

So that's not what limits their population growth.

Rather, the amount of food, like a specific fish that they both eat, could be limiting,

while other resources are plentiful.

Second, as the overwhelming diversity of life in almost any community shows us, most species --

even ones that are almost identical to each other -- are adaptable enough to find a way

to survive in the face of competition.

They do this by finding an ecological niche, the sum of all resources, both biotic and

abiotic, that a species uses in its environment.

You can think of an organism's niche as its job in the community that provides it with a certain lifestyle.

We tend to keep jobs that we can do better than anyone else in our community,

and if we're desperate, we do a job that nobody else wants to do.

But no matter what job we have, what it pays in terms of resources dictates our lifestyle.

So finding a nice, comfy niche that you have pretty much to yourself not only provides

a steady income of food and other stuff,

it also allows a species to avoid competitive exclusion, and this, in turn, helps create

a more stable ecological community.

It's and elegant and peaceful solution, I wish that we humans could figure out something as good,

but as with anything in life, this relative security and stability comes at a price.

The bummer is that it prevents some species from living the lifestyle that they could

have if nobody else competed with them at all.

This ideal situation is called a fundamental niche, and it's just that, an ideal.

Few, if any species ever get to live that way.

Instead, because of the need to avoid competitive exclusion in order to survive,

many species end up with a different job, and hence lifestyle.

It's not necessarily the job that they studied for in college, but it makes a decent living,

and that's called a realized niche.

This, my friends, is how nature does conflict management.

But it sounds kind of unnatural, doesn't it?

I mean, Gause taught us that competition, and winning the competition, was the natural order of things.

So how could it be that part of the natural order actually involves letting everyone compete and win just a little bit?

And how did we ever come to discover that things actually worked this way?

Well, it took a special kind of person, and to to tell you about him, I'm going to need a special kind of chair.

Canadian born ecologist Robert MacArthur was in his late 20s when he made a discovery

that made him one of the most influential ecologists of the 20th century.

While researching his doctoral thesis at Yale University in 1958,

he was studying five species of warblers that live in coniferous forests in the northeastern United States.

At the time, because there were so many different species of warblers that lived, fed, and mated in such close quarters,

many ornithologists thought that the birds occupied the exact same niche

and thus were an exception to Gause's competitive exclusion principle.

But MacArthur was not convinced.

A mathematician by training, he set out to measure exactly how and where each kind of

warbler did its foraging, nesting, and mating.

In order to do this, he studied each tree the birds lived in, dividing them into zones, 16 zones to be exact,

from bare lichen at the base of the trunk, to new needles and buds at the tips of the branches.

After many seasons of observing many birds in many trees,

he found that each species of warbler divided its time differently among the various parts of the tree.

One warbler, called the Cape May, for example, spent most of its time toward the outside of the tree at the top.

Meanwhile, the Bay Breasted fed mostly around the middle interior.

MacArthur also found that each of the warblers had different hunting and foraging habits

and even bred at slightly different times of the year, so that their highest food requirements didn't overlap.

These differences illustrated how the warblers partitioned their limiting resources,

each finding its realized niche that allowed it to escape the fate of competitive exclusion.

The phenomenon he observed is now known as resource partitioning,

when similar species settle into separate niches that let them coexist.

Thanks in part to this discovery, MacArthur became known as a pioneer of modern ecology,

encouraging curiosity and hypothesis driven research, championing the use of genetics in ecological study,

and collaborating with biologists like E. O. Wilson and Jared Diamond.

Sadly, he died of renal caner at the age of 42,

but his study of northern warblers remains a classic example of community ecology that is still taught today.

So, if organisms can do this, if they can behave in ways that help minimize competition

while increasing their odds for survival,

it follows that traits associated with this behavior would start being selected favorably.

After all, that's what natural selection is for. When this happens, it's known as character displacement.

To demonstrate, let's go back to some other famous ecologists,

our favorite couple of evolutionary biologists and love birds, Peter and Rosemary Grant.

I told you before about how they observed the process of speciation among Darwin's famous Galapagos finches.

Well on the same island, Daphne Major, in 2006, they witnessed character displacement in action.

For a long time, a small population of finches had the island to themselves,

where they ate a variety of seeds, including seeds of the feverplant,

which were bigger and more nutritious than the smaller seeds that were available but

were harder for the little finches to open.

Then in 1982, a group of much bigger finches showed up on the island,

and they began to commandeer the island's abundant supply of feverplant seeds.

Within just 20 years, the Grants found that the small finches' beaks shrunk to allow them

to specialize in eating only the smaller, less nutritious seeds.

But now the little finches had those seeds all to themselves.

The traits of the two populations had actually diverged to help facilitate the partitioning of resources.

See? Competition can be hard on us, but it also can make us better people,

or you know, finches or warblers or kangaroo mice.

But there are also kinds of interspecies interaction in which species actually join forces in the fights for survival.

This is the ultimate in conflict-avoidance.

In these cases species in a community actually manage to avoid competition altogether

by forming downright tight relationships that benefit one, if not both, of the parties involved.

You may have heard of both of these cases: First, mutualism, where both species benefit,

and commensalism, where one species benefits and the other is kind of like, "Whatever."

Mutualism abounds in nature, and for those who've been paying attention to Crash Course,

you've heard me talk about it many, many times before.

A prime example [of mutualism] are mychorrhizae, the fungal root that we talked about a few weeks ago,

where fungi and plant roots get tangled and essentially rub each other's backs for nutritious favors.

Others you may have heard about include flowering plants that produce nectars to attract pollinators,

and that bear fruit to attract animals to help spread the seeds inside.

Oftentimes these relationships become rather needy, like in the case of termites --

they can't break down the cellulose in the wood they eat without the enzymes produced

by the microorganisms that live inside their digestive systems.

Without the little critters, the bigger critters would die.

Such a needy relationship is called obligate mutualism.

By contrast, commensalism is where one species definitely benefits and the other isn't really hurt or helped.

Such neutrality, of course, is difficult to prove because even a seemingly benign interaction probably has some effect.

Barnacles, for example, hitchhike on gray whales, getting a free ride through swaths

of plankton-rich water for feeding.

While clearly a benefit to the barnacles, the relationship is often considered commensal

because the whales probably don't really care whether the barnacles are there or not.

Or do they? The barnacles might slow down the whale as it swims through the water,

but on the other hand, they might also serve as a type of camouflage from predators like orcas,

in which case they confer an advantage.

So it probably comes down to "meh" for the whale.

And when you consider all the other possibilities out there when species interact, "meh" isn't such a bad option.

Especially considering that next week, we're going for the throat,

by which I mean we'll be investigating the kill-or-be-killed world of animal predation

and all of the fantastic evolutionary changes it can trigger that lead to even greater diversity in ecological communities.

There probably is going to be a lot of blood though, so you might want to bring your poncho.

Thank you for watching this episode of Crash Course: Ecology.

If you want to review anything, there's a table of contents over here for you to click

on any of the parts that you may want to review.

Much love and appreciation to all the people who helped us put this episode together,

and if you have any questions or comments or ideas, you can leave them for us on Facebook or on Twitter,

or, of course, down in the comments below.