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Ecology, Part I


  • Intro 0:00
  • Ecology Basics 0:05
    • Ecology
    • Biotic vs. Abiotic Factors
    • Population
    • Community
    • Ecosystem
    • Biosphere
  • Individuals and Survival 4:13
    • Habitat
    • Niche
    • Symbiosis
  • Obtaining Energy 11:14
    • Producers
    • Consumers
  • Food Chain 17:11
    • Model to Illustrate How Matter Moves Through Organisms in an Ecosystem
    • Examples
  • Food Web 20:29
  • Keystone Species 22:55
  • Three Ecological Pyramids 27:28
    • Pyramid of Energy
    • Pyramid of Numbers
    • Pyramid of Biomass
  • The Water Cycle 37:24
  • The Carbon Cycle 40:19
  • The Nitrogen Cycle 43:34
  • The Phosphorus Cycle 46:42
  • Population Growth 49:35
  • Reproductive Patterns 51:58
    • Life History Patterns Vary
    • r-Selection
    • K-Selection
  • Density Factors 59:02
    • Density-Dependent Factors
    • Density-Independent Factors
  • Predator / Prey Relationships 1:03:59

Transcription: Ecology, Part I

Hi, welcome back to, this is the lesson on ecology, part 1.0000

First, we are going to talk about some basic terms that really encapsulate ecology as a whole.0006

These are very important terms that come up again and again, related to how organisms relate to each other and to their environment.0012

First off, ecology is the study of the interactions that take place between organisms and their environment,0018

and also organisms between each other.0024

Qualitative and quantitative data informed us.0029

Qualitative data is when we are talking not about numbers, but in terms of the quality of things.0031

If you look outside and it is a rainy day, you are not talking about exactly how much rainfall there is.0040

Or maybe an organism is stressed in their environment, you can tell they are stressed by their behavior.0046

You may be talking about descriptors about that particular organism and it moving around in a peculiar way that is not normal.0052

That would be qualitative data.0060

Quantitative data would be all those things involving numbers.0063

If there is a 3cm of rainfall in a day, that is quantitative.0068

If an organisms energy consumption is a particular amount per day,0073

we can measure exactly how much organic compounds they are consuming.0080

Biotic versus abiotic factors, if it has to do with life, I will underline it with green because green is photosynthesis and it supports life.0084

Biotic, any particular organism that exists in an environment, whether it is a parasite,0095

whether it is producing energy for community as does a plant,0105

or whether it is consuming energy because it is heterotrophic, that would be a biotic factor.0109

If it is abiotic, it is not alive.0117

An abiotic factor would be rainfall, though water supports life, water in itself is not alive.0120

Temperature would be an abiotic factor.0128

The amount of sunlight would be an abiotic factor.0133

These particular factors definitely have an impact on environments and the organisms that live in them.0136

A population, this term has come up numerous times in this course, in evolution, it comes up.0143

In ecology, a population is the same definition.0149

It is a group of individuals of the same species in a specific area.0152

If they can all mate and have offspring, and they are in one particular habitat, that is a population.0157

If we are talking about more than one type of organism in an area that is bigger than a population, and that would be a community.0165

A community is many populations living in an area.0173

If we talk about a food chain, what organisms are eating what, in a particular habitat?0176

That would be a community.0182

Bigger than that, if we consider the whole community and its environment,0184

in terms of all the factors that impact that terrain in those organisms, then we are talking about an ecosystem.0190

An ecosystem is populations of all species living in a particular environment and all those abiotic factors,0198

in addition to the biotic parts of it.0204

And then, the biosphere, it is the portion of earth that supports life.0207

Here is earth, it is the upper parts of the crust, the oceans, the lakes and rivers, the land masses,0213

those parts that support life, where you can find life on earth.0224

In the center, the core of the earth is much too hot, too much pressure, etc. , to support life.0229

If you are wondering about term biome, if you have heard about biome, the different kinds of ecosystems are called biomes.0236

We will cover the biomes later on in this course.0249

Individuals and survival, we have to keep in mind some terms associated with how individuals maximize their success.0255

You can find individuals in their own habitat.0263

This is a term most people know, it is the place where an organism lives its life.0266

That could be in the water, it can be on land, it can be a little bit of both depending on the organism.0271

A niche, depending on who you ask, I prefer to say niche.0277

A niche is all strategies in adaptations an organism uses in its environment.0281

That is a lot to remember, in terms of the definition, I think the easier way to remember is just think about its role.0287

What does the organism do and what is it provide in the particular habitat that it is in?0294

If you consider this organism here, this is a millipede, it does not actually have a thousand feet, but to it has a lot.0300

It has 4 little legs per segment and ends up being a lot of them.0313

A millipede is an herbivore, part of its role is that it munches on plant life and lichens,0317

which is a combination of a fungus and algae together in a relationship.0325

That is part of its role, the fact that it is an herbivore in its environment.0330

Another part of its role is that, it gets eaten by carnivores, birds will eat it.0334

In terms of where an animal resides, where it actually makes its little home and habitat, what it does on a daily basis,0340

how it fits into the food chain of what eats it, what does it eat, those are all part of its role, its particular niche.0348

In terms of competition, if two organisms in one habitat try to occupy the same niche,0356

you are probably going to have one being more successful than the other.0364

Potentially, one of them will only be able to exist in that niche.0367

A good example would be, if you consider a squirrel and a chipmunk, those are similar rodents,0372

squirrels have bushy tail and chipmunks do not, different species of rodents.0387

If they try to occupy the same tree and they are trying to eat the same foods in the same area,0392

the competition goes way up, that is pretty intense.0400

The best choice for them would be to try to occupy different trees in that community.0403

You can maximize the effectiveness of those two different organisms being successful, in terms of them getting food.0408

That is known as the competitive exclusion principle, in terms of them trying to occupy the same niche,0417

not the best idea in terms of long-term success.0423

When we talk about organisms relating to one another throughout their lives and dependency between different species, we call it a symbiosis.0427

Symbiosis literally means living together.0436

Mutualism is the most commonly talked about form of symbiosis.0440

It is a positive relationship for both, I scratch your back, you scratch mine, kind of thing.0444

A good example would be lichens, I just mention those a moment ago.0454

A lichen is a situation where you have a sac fungus that has algae living on it.0459

The algae gets benefit because it is able to exist on land, like in a forest, where you normally would not find algae.0472

Typically, you will find it near the shore or in the ocean, or in the lake.0478

But, you can have algae on these little sac fungi and they have a little home, they are being cradled by that fungus.0482

How does the fungus benefit from the algae?0490

The algae is doing photosynthesis and can provide sugars to that fungus.0493

They are both benefiting out of the situation.0498

Another example would be commensalism.0502

Commensalism is where it is positive for one but neutral for the other, meaning the other, whatever it is not positive, it is not negative, it is okay.0504

An example for that would be, there are cases where you have a shark patrolling, moving through the water, hunting.0519

You will have tiny little fish that kind of use the shark, in terms of helping them more easily navigate through the water.0526

That is like a race car driver driving behind another car, it is easier for them to make the way through, or if you are a bicyclist.0537

The other thing is that they get protection by being next to the shark, it is unlikely that some other fish is going to go after it.0549

The little fish get some benefit out of that.0561

They probably are not going to be in this quickly.0564

They are also not going to be where the shark.0567

The shark is going after bigger prey, and the shark is not going to spend its energy0569

trying to get those little fish that are this big and swimming near the back of its tail.0574

The shark does not really care, the shark does not have a negative result from that at all.0579

Parasitism is positive for one and definitely negative for the other.0586

A parasite feeding on a host.0597

A case there would be tapeworm in human or any other animal that can get a tapeworm inside of its digestive tract.0600

The tapeworm is definitely getting the positive, it is feeding off of partially digested food inside an organism.0613

The human is not feeling good, very uncomfortable, and it keeps growing inside of you.0621

It is just not a good thing.0625

Another example would be a foot fungus, athlete's foot growing on the bottom of the foot.0628

The fungus gets benefit because it is feeding off of your skin cells.0634

It is very uncomfortable, itching, and burning for the host.0637

Another example of commensalism is actually this picture right here.0641

If you are wondering what is going on here, you got these big trees with Spanish moss.0645

Spanish moss will hang from the branches and not negatively impact the large tree at all.0653

The large tree does not care but the Spanish moss gets closer to sunlight out of this.0660

It is actually being much higher up, it can do more photosynthesis, thanks to these large trees.0667

That is another example of commensalism.0672

In terms of obtaining energy, the flow of energy can be traced as it moves through a community,0676

from one level to the next, from the bottom up to the top.0681

In terms of the bottom, in terms of where the energy originates, we have to talk about producers.0684

They are producing the organic compounds that end up feeding whatever is eating it,0691

and eating the thing that eats it, and so on, and so forth.0697

Producers, typically, they are getting their energy from the sun.0700

The sun is powering these producers, that is the energy source that keeps organisms on earth alive.0707

There are examples of organisms that do not directly rely on the sun, I will mention that in a second.0713

We can also call producers autotrophs, self energizing autotrophs,0718

they make their own food which supports their cells, plants do that.0726

If they are using the sun, let me highlight this for you.0732

If they are using the sun, they are photoautotrophs, because photo means light.0740

A photoautotroph, classically a plant.0746

If they are not using light, if they are using chemicals like inorganic gases, for instance, they will be chemoautotrophs.0749

An example of a producer in a community that is getting energy into the system, into the other organisms above it on the food chain,0758

you can think of the bottom of the ocean, the bottom of the ocean where there is absolutely no sunlight down there.0768

You can have hydrothermal vents, we have all kinds of gases coming into the water.0774

These particular bacteria down there that are chemoautotrophic, they take these gases into their cells and they can make nutrients.0779

There is something that eats the bacteria, those would be consumers.0788

That ends up feeding the whole system.0792

These are self energizing with chemicals, specifically inorganic gas compounds.0794

This here, you have got a classic photoautotroph, this is a green algae on the shore near a body of water, that is a lot of green algae.0801

The consumers, like the economic term, in terms of consuming goods and products,0812

in the biological world, consumers they are consuming organisms.0822

They are consuming organic matter to feed themselves.0826

Anything that eats is a consumer.0829

They are heterotrophs, they are getting their energy from another source, outside of themselves, other than themselves.0832

This could be carnivores, where they are eating meat, they are eating other animal bodies dead or alive.0845

Omnivores, like us, eating all, that is what omni means.0853

We eat plant matter and animal matter.0862

There are some individuals in the human species that have chosen to not eat animal tissues,0867

they are vegetarians or vegans, in some cases.0876

That is their choice, biologically, in terms of the enzymes we are able to make,0880

in terms of what we are meant to eat in terms of the revolution, we can eat animal tissue.0885

That is natural for us to do that.0892

You got to have plants, you cannot be a carnivore.0895

Herbivores, eating only plant material.0899

Insectivores, these would be eating insects like an anteater or an aardvark.0902

There is an aardvark, similar to an anteater, in terms of what it relies on for food0909

but not very closely related to it, in terms of mammalian orders.0916

If you look at the other lessons earlier on in this course, regarding the orders of mammals,0923

aardvarks are in order by themselves called tubula dentata, because of their weird shaped teeth.0931

Aardvarks are insectivores.0939

Fruibivores, eating fruit, there a lot of fruit bats out there that rely on fruits and there are lots of other varieties.0942

There are even spongivores, there are sea turtles that rely on eating sponges completely.0950

Then, we have decomposers, they are heterotrophic, in a sense that they have to feed on something else.0958

What makes them unique is they are just breaking down tissue, oftentimes dead tissue.0964

Their response for getting those organic nutrients back into the soil, available to producers as vitamins, in a sense.0974

In terms of fertilizer, the plants rely on in the soil, what they can take it to their roots, thanks decomposers,0983

dead bodies get reincorporated back into the soil and allowing plants to support themselves.0991

Without plants supporting themselves, consumers are not going to be able to be supported.1000

Oftentimes, decomposers are bacteria, fungi, insects, worms, those are several examples.1005

In this picture right here, you have got mold eating these fruits.1024

Food chains, there are model that illustrates how matter moves through organisms in an ecosystem.1033

It is literally a chain of organisms, this is eaten by this, which is eaten by this, etc.1040

In the next slide, we will have a more complex food web which is more realistic depiction of how it actually happens.1045

It is not always that just one eats the one, eats the one, eats the one, but you have various food chains within food webs.1051

Typically, it goes from autotroph, whether its photoautotroph or chemoautotroph, to supporting heterotrophs.1057

There could be many heterotrophs in the food chain, there could be 3 of them, there could be 4 of them, potentially.1065

And then, decomposers, the reason why I have this in parenthesis is because,1072

if you think about like the top carnivore in an environment, it might be a bear,1079

sometimes it might be a human, you do not think about something eating them.1085

When that organism dies, its body does get decomposed back into the soil, like I mentioned on the previous slide.1090

Decomposers are definitely important part, in terms of getting these heterotrophs and their matter,1098

back into the food chain, in a sense recycling their matter.1105

Examples of food chains, this picture right here is this top example.1111

A berry bush, it is a producer, it is an autotroph, it is doing photosynthesis and it is making these lovely fruits to spread it seeds around.1114

Something like a mouse, little mice, will eat the berries.1125

Oftentimes, they are little herbivores.1131

These herbivores are eaten by carnivores like black bear.1134

Actually bears, oftentimes are omnivorous, they are usually omnivores.1138

Bears, they will eat fish, they will eat little animals, but they will also eat nuts and fruits, and other herbs and such.1146

This is definitely a heterotroph that is above the food chain, on this particular lineage or this line.1157

Another one, cyanobacteria which is not talked about a lot but very important worldwide,1167

cyanobacteria is a kind of bacterium that does photosynthesis.1172

Cyanobacteria, they exist all over the oceans.1178

Cyanobacteria can be eaten up by hermit crabs.1184

This producer is feeding this particular consumer.1187

This consumer, if it gets closer to a sea anemone, it gets eaten.1193

A sea anemone is a carnivore, a very simple animal in terms of its body design but deadly,1198

with its nematosis that sting hermit crab and paralyze it, and it gets eaten whole.1204

Grass is a producer, an autotroph that supports the herbivorous rabbit.1210

This consumer is eaten by this consumer, the fox, typically carnivorous.1217

And then, the fox get picked up by an eagle, and lunch for the eagle and its little eagle babies.1222

A food web is like a bunch of food chains together.1230

You could see how it kind of exists as this big picture.1234

In the Chesapeake Bay, you can find these various organisms and more.1239

I just want to clarify something.1243

Typically, primary consumers are herbivores.1245

In this line, you have primary producers which are at the bottom.1252

They are the ones doing photosynthesis, typically.1259

They are eaten by organisms that eat plant material.1262

That would be the primary level, the first level of consumers.1266

They are herbivores, since they are eating the primary producers.1271

With that point on, it is consumer eating consumer, eating consumer.1274

Secondary consumers, they eat primary consumers.1278

Tertiary consumers, eating secondary consumers.1281

You can have some scenarios where occasionally, you can have a secondary consumer1284

that actually will feed on the primary consumer and the primary producer.1290

Specially, if it is an omnivore, like a bear, if it is eating both primary consumer as the mouse and eating nuts or eating fruits, and such.1296

Let me go over few of these examples.1310

Phytoplankton, little microscopic beings that do photosynthesis, that would be primary producer.1312

There are other vegetations in this Chesapeake Bay.1318

You can have these little invertebrates benthic, that is a level in the lake or in the bay, in this case.1322

You got invertebrates feeding off this little phytoplankton, they can be eaten by sea ducks.1330

You can also have zooplankton being eaten by little bivalves like clams and such.1337

You can have birds eating those, bald eagle and an osprey, these are these tertiary consumers that are feeding off1344

of the secondary consumers such as these, which are feeding off of the primary consumers which were eating the producers.1350

That is a food web, inevitably these organisms die and the decomposers help break down their bodies and get those nutrients in the water.1360

They are supporting the producers.1370

Keystone species, this is a species that if removed from the population, or from the community specifically,1376

has a disproportional effect on the rest of the food web relative to its abundance.1383

What I mean is, if you look at this particular food web, both on land and in the water, it is pretty complicated.1389

Just because there is a lot of one organism does not mean they are the most important.1399

They all have importance in feeding something else and keeping certain populations in check,1403

keeping certain populations from getting out of control.1410

But, there are certain organisms that if you remove them, they may not be the most abundant organism,1412

but taking them out of the situation just messes up the whole scenario.1418

Whatever they were eating gets out of control, in terms of the population abundance and1424

they are eating too much and they can throw the whole thing into chaos.1429

The biodiversity goes down the tubes.1436

I will give you an example or two.1438

One of the classic ones is pisaster, if you are wondering what is pisaster, it rhymes with disaster.1440

If you take out pisaster, it is going to result to disaster.1450

Pisaster is a kind of starfish or sea star, that is what I prefer to call them because they are not fish.1453

In intertidal communities, usually in shallow areas, if you take out the sea stars, for some reason,1461

let us say there is a virus or they are taken out by humans too much, because people want to eat them, whatever the case is.1469

They feed on certain organisms and they are responsible for keeping those organisms in check,1478

one of them would be mussels, which is a bivalve related clams and scallops, etc.1484

If they are not feeding on them, they can get way out of control.1493

There have been studies where, to see the effects, they removed the sea stars to test this theory.1496

You go back 10 years later or more, it looks like the population is all mussels.1503

The biodiversity has gone down the toilet.1509

Biodiversity is very important, that will be mentioned a little bit later in this course,1514

in terms of the value of having a lot of different organisms in a community.1518

In terms of this whole scenario, I’m going to highlight a few organisms, in terms of the relative importance.1523

If you are going to take out all of these toads, the toad in this case could be the keystone species.1532

I do not know that for sure, I have not specifically gone into this community and investigated that, in terms of the toad’s impact.1540

When we look at all the arrows going to the toad and from the toad, the toad is responsible for eating a lot of different organisms.1547

You can see that it is eating these insects, it is eating these particular insects from over here.1554

It can also eat these little slugs.1563

The toad is responsible for eating a lot different organisms and a lot of organisms eat the toad.1567

It is possible that, if the toads all get sick, they all have some kind of disease and they die off.1573

It could end up decimating this community, in terms of all these different organisms1582

relying on one another in this set of food chain or this food web.1588

In this aquatic environment, the keystone species may actually be this organism.1593

Why, it feeds off of a variety of organisms from here, it supports these fish, or in this case this is a mammal, it is a dolphin.1609

This particular fish, though it may not be the most abundant organism or the abundant species, it could be the keystone species.1620

Removing this is way worse than removing this or removing this.1628

Enough study in a particular community, in terms of what relies on what and what is keeping what population in check,1634

can reveal which of these organisms is proportionally most important.1641

Three ecological pyramids, in terms of the movement of energy from producer on up through consumers.1649

We can look at it in a variety of ways.1655

The pyramid of energy would look like this.1658

There is a pyramid, the pyramid of energy.1669

At the bottom, we are going to have grass, the grass is the producer.1682

Here I will write primary producer.1694

By the way, this symbol 1 with a little circle, that is a notation that means primary.1701

Secondary will be a 2 with that little symbol, etc.1707

If we look at grass, in terms of the amount of energy it is producing because of photosynthesis getting CO₂, water, and sunlight together,1710

and making sugars, we are going to say 100% of the energy that starts off this community, in terms of fueling it is right there.1720

Next up the line, we are going to have grasshoppers.1731

This particular insect feeds on grasses, this would be the primary consumer.1742

When you consider that the grasshopper is eating all this plant material,1752

the actual amount of energy from the plants that directly gets into the grasshopper,1758

in terms of getting in its body and sustaining it, it is a 10% transfer.1764

The transfer from here to there is actually from 100% to 10%.1769

If you are wondering, why the heck does that happen, where does the other 90% go?1775

In terms of the efficiency of organisms getting food in the body and1779

converting that into ATP to that energy molecule that fuels our cells, it is not the most efficient process.1784

Just like where we can consider combustion engine in a motor vehicle, it is not 100% efficient.1793

I have heard that it is closer to like 40% efficient or even less, with the gas engine.1800

It is similar with our bodies, a lot of the energy is lost as heat in those metabolic processes that happen,1805

in terms of getting that grass in the body and digested.1812

Just the processes of breaking things down, it is not the most efficient energy transfer.1820

Only 10% goes from this level to the second level.1826

Then, something eats the grasshopper, that would be the secondary consumer.1830

That is going to be birds, these would be the secondary consumers.1836

As you may have guessed, once again, the 10% rule, 10% from here to there.1847

It is just 1% here from the total that was in the grasses two levels below.1856

Birds are eating grasshoppers, they have to eat a lot of grasshoppers to sustain themselves.1862

Something is going to eat the bird and it is going to be the fox.1868

This is the tertiary consumer and 0.1%, and that is the 10% energy transfer rule from producers on up to the top consumer.1875

Pyramid of numbers, this is when we look at the actual number of organisms in each of these trophic levels.1899

That is what the term is for these particular levels in the pyramid.1907

You can call it trophic levels, there are 4 of them there.1913

We are going to use the same organisms in the community up above.1924

We are also going to have grasses, grasshoppers, birds, and foxes.1937

We are going to say that with grass, maybe there are 3000 of them, 3000 of these grass plants.1947

They are sustaining 250 grasshoppers.1961

You can imagine that, if you have 3000 grass plants and you have 3000 grasshoppers, you probably run into a problem.1972

The grasshoppers would completely decimate or destroy the producers that are supporting them.1982

As you could see with these pyramids, the reason why it goes from large up to small, in terms of numbers,1989

is you cannot sustain it if it ends up being like this.1996

You need to have a solid base because that energy supporting every level above it.2001

You are going to see you less and less numbers as we go up the consumer ladder.2008

Next you have the birds, we will say that we got 25 birds.2014

Fox, there are two of them, a mating pair of foxes up the top.2027

Once again, if you have 25 birds and they were 21 foxes, chances are the foxes are going to eat all the birds and there is going to be a problem.2033

That is going to throw the whole thing out a whack.2044

Pyramid of biomass, that is good enough.2048

Here we are going to have 3 levels.2067

At this lowest level, we are going to talk about grain that is supporting some cattle.2075

We have got 100 kg of grain, that is producer, primary producer autotrophs.2084

This next level, what is relying on that grain.2099

We are going to say that, that exact amount of grain is helping to produce or make 10 kg of beef.2102

Obviously, a cow, an actual steer is going to have a lot more weight than that, in terms of kilograms it is going to be way heavier.2116

What this is saying is that, that amount of grain is required to support that amount of beef,2129

in terms of producing that tissue and sustaining that tissue.2136

That amount of beef can help produce 1 kg of human tissue.2140

A steak, a hamburger, whatever it might be.2154

What is this remind you of, the pyramid of energy that 10% transfer.2160

10 is 10% of 100, obviously, 1 is 10% of 10.2167

This goes back to that pyramid of energy, this is actually accounting for the actual mass of what is in these biological organisms.2172

This information here informs a lot of people who wish that there were more vegetarians and vegans in the world.2183

Because of poverty levels world wide and situations that are sometimes beyond people's control, in terms of political turmoil.2193

There are various population of humans that do not get enough food world wide.2202

There are billions of people that are malnourished, in terms of not getting enough nutrition.2207

People claim that, if we took all the grain that is required to sustain all that cows we have,2215

for the beef demand and cow milk demand, etc., there will be plenty of grain that will go around.2222

That maybe true mathematically, but it is hard to make those changes in people's lives.2230

Here are three ways of looking at energy transfer up through food webs or food chains.2237

There are various cycles in terms of how inorganic molecules move throughout an ecosystem.2246

Water is extremely important in sustaining life.2256

All life really depends on water for its origins.2260

A certain amount of water in its body and water in its diet, typically.2264

There is a lot going on, you may want to pause and just take this in.2269

Some of it, I’m not going to mention because this is such a busy, just full of terms and words, kind of diagram.2275

I like that it has all the stuff in here.2283

We are going to focus on certain parts of it.2286

For instance evaporation, evaporation from the ocean, you are going to have water going from liquid to gas.2290

As water ends up in the atmosphere, you get condensation.2300

Condensation is that term that is used for when you have a cold beverage and you get those droplets of water on the outside.2308

It is not that the water actually went through the glass, that is not it.2318

As a child, I was very perplexed, where did it come from?2321

It is because that temperature is so much colder than the water molecules and the air surrounding it,2324

that those little water vapor molecules are going condense.2332

There are to get to be liquid droplets on the outside because they have been cooled down so much.2337

In terms of forming clouds and getting to precipitation,2342

you can have water vapor condensing on dust particles in the air, that is how you get clouds.2346

And then, you have rain and snow, and lots of types of precipitation.2353

That is what all of this is referring to is precipitation.2358

That gets the water back down to land, back down to the bodies of water.2365

They talk about surface runoff, in terms of water ending up going back into rivers and oceans.2371

Groundwater ends up getting back in here.2379

When it is snowing up in the mountains, especially when springtime rise,2384

you get that snow melting and it runs off into the rivers that end up in lakes, back in the ocean.2388

It is that cycle that gets water from the land to the oceans backup in the air, lining again to support plant life.2394

Without producers getting water, it is going to be hard for consumers to get their energies.2404

Water cycle is very important, in terms of going from liquid to gas, and back again.2411

The carbon cycle, carbon is in every living being.2421

But in terms of it going from particular organisms up at the atmosphere and back, we have to consider how that happens.2426

There are always CO₂ in the atmosphere.2435

If you are wondering what are these numbers that you are seeing.2437

This is in gigatons, in terms of the amount of carbon that we see in these different parts of the biosphere.2440

The atmosphere you get CO₂ there.2448

What contributes to the increase in CO₂ overtime is fossil fuel.2452

Burning fossil fuels releases greenhouse gases, among them is CO₂.2459

We are adding CO₂ to the atmosphere as the years go by.2464

This is why planting trees is important and this is why reducing the number of trees2468

that we are chopping out every year is also important.2474

What keeps this atmospheric carbon level, in terms of how much is there in acceptable levels,2477

in terms of warming our planet, what keeps that at the right level is plants doing photosynthesis.2484

This arrow coming out of the atmosphere into plants, that is thanks to photosynthesis.2490

When all these leaves open up their stomata and take in CO₂,2495

they are getting CO₂ out of the atmosphere and into carbon based molecules such as sugars in the plants.2499

That is feeding cattle and other herbivores.2506

And then, the herbivores, their carbon ends up in the consumers and carnivores, and so on.2513

It ends up in soils inevitably because organisms die whether it is a plant, whether it is an animal,2519

you do get carbon compounds ending up in the soils.2528

It also ends up in the oceans, you get it coming from rivers.2531

You get it coming from algae, the amount of photosynthesis happening in the ocean is incredible,2538

in terms of the biomass that is generating those sugars.2547

Algae are getting CO₂ into their cells and you have organisms feeding off of that.2552

Inevitably, you can have CO₂ and other carbon based compounds ending up in sedimentary layers.2560

As organisms die and their bodies and cells detritus, it is what is called,2569

settles down to the bottom and ends up in sedimentary rock.2574

Long-term, very long-term, how do you think we end up getting fossil fuels?2578

You get it from underground.2585

It is part of the cycle, what ends up down here, we end up burning as a fossil fuel.2589

Thanks to plants, a lot of that CO₂ that we are putting up in the atmosphere with our factories and cars, etc.,2599

we can get it back into organisms and control the amount of carbon that is actually in the atmosphere.2608

The nitrogen cycle, nitrogen is important for making proteins, for making DNA and RNA.2615

Nitrogen is in those compounds, it is in every organism.2623

Nitrogen in the atmosphere that is the most abundant gas molecule in the atmosphere.2627

It is close to about 78% of our atmosphere.2634

Atmosphere and nitrogen, it is up there, how does it get out of the atmosphere and back?2638

Here is how, you actually get nitrogen into getting into soils because of bacteria.2642

These nitrogen fixing bacteria living in the legume root nodules.2651

It is an example of symbiosis, where you have these bacteria that are able to take nitrogen gas.2661

Through the molecules they have, they have like magnetism to get that nitrogen stuck inside of them2670

and incorporate it into organic compounds and in organic compounds, in terms of what they are producing.2678

You can have the process known as ammonofication, the production of ammonium.2686

Nitrogen is a part of the ammonium compound.2692

These nitrifying bacteria can help reduce nitrites and nitrates, slight difference in terms of the amount of oxygen found in them.2695

All of these are important as fertilizer, in a sense.2705

If you look at the main ingredients in a fertilizer that you buy at the store, we are talking nitrogen containing compounds.2709

It is like vitamins for plants.2716

Plants do not just need CO₂, water, and light.2718

Yes, that is important in photosynthesis, it is necessary.2723

But they also need compounds from the soil, like these nitrogen containing compounds.2726

You have this process called assimilation.2732

Assimilation is the way that plants get these nitrogen compounds into their bodies and it ends up in other organisms.2735

This little rabbit here that is feeding off of plants, that is how we get its nitrogen, in terms of replenishing its protein levels.2744

And, when it copies its DNA and makes new DNA and RNA, it needs nitrogen to have those raw materials.2754

Organisms are going to eat the rabbit, etc.2762

When organisms die, their nitrogen can also get incorporated back into the soils.2765

Assimilation is the way that plans get these nitrogen containing compounds back into the producers,2770

back into the life that is supporting what is above the surface.2779

Decomposers are instrumental in not only decomposing plants but other organisms like when a rabbit dies.2782

That is not just mushrooms, it is also bacteria.2792

Bacteria and fungi, major decomposers, an important part of cycling nitrogen through the biosphere.2796

Finally, the phosphorus cycle.2804

Phosphorus not as popular as the other three that I just told you about.2806

But, arguably just as important.2810

Phosphorus, you find that in a lot of important compounds, DNA and RNA among them.2812

Phosphorus, needed to grow and develop as an organism.2819

Without it, you cannot do that.2822

There is a short term phosphorus cycle and then there is a long-term one over here.2824

The short term one, in terms of phosphorus supporting those different trophic levels I mentioned earlier.2830

You have soils with plants in them.2838

Those plants are able to take in phosphors containing compounds into their bodies.2842

Animals end up eating those plants, it gets into their bodies.2848

Fertilizer runoff can sometimes result in phosphates ending up back into the soils.2853

Also, weathering and erosion gets phosphates into the water.2859

I just realized whoever made this spell phosphates, the word post fates.2866

This is spelled phosphates, they have post spelling.2871

It is phosphates, just to clarify.2881

Dissolved phosphates end up in marine base life, like algae and other plants2884

that do photosynthesis and marine animals that feed off of those.2890

Similar to the producer-consumer food web or food chain up on the surface.2893

In the long run, in terms of a long-term cycle, when organisms die, they end up in the sediment, in the sedimentary rock layers.2902

In the long run, phosphates and other phosphorus containing compounds, specifically phosphates end up in the rock formations.2915

Overtime, you can gradually get layers of earth being pushed up, in terms of mountains being formed.2923

We were talking over millions, billions of years.2931

This actually ends up contributing to phosphates that end up in river water.2936

River water associated with rain that you get from high up in mountains and rivers run to the sea.2941

You can get lots of phosphates ending up in river water that came from rocks in the mountains,2950

that you can trace back to just millions and millions of years ago, in terms of what died in oceans, a long time ago.2957

It is interesting to compare the short term phosphorus cycle to2965

how the long-term phosphorus cycle also contributes to the overall phosphorus cycle.2969

Population growth, a very important part of ecology.2977

As I pointed out in the evolution lessons, resources are limited.2980

There is only so much food, so much water, so much a light, so much space.2986

That is going to put limits on how big a population can get, in terms of the overall numbers.2992

When we only look at different growth patterns in populations, in terms of how they grow over time, there are two main trends.2998

That J curve also known as exponential growth, this looks like a J and the S curve looks like an S, that is known as logistic growth.3004

This curve right here, you are seeing the S curve.3015

N for the number of organisms, T for time, this right here is known as the carrying capacity.3019

You can have organisms exceed their carrying capacity but once they do, you are going to have a drop.3029

This came up in the evolution as well.3037

Let me actually draw a J curve, that will be like this.3040

See how it just boom, it just goes up exponential, like an exponential graph.3047

I have heard one example of this as like houseflies in your house, that is a pest, we do not want flies to be in there.3053

If you are not killing off the flies and getting rid of whatever they are feeding off,3060

whether it is rotting food or dirty dishes, or whatever, the amount of house flies will just continue to increase.3066

It will look like exponential growth for probably a while, this J curve.3072

Inevitably though, there is a carrying capacity even for your dirty house or dirty apartment.3080

Eventually, this will drop because there would not be enough material, enough food in that area,3086

enough space in the area to sustain that population.3093

Inevitably, these exponential or J curve population growths do taper off, typically.3095

An S curve like you can see here, it increases and increases but then slows down as you get limits,3102

in terms of the amount of resources available.3109

There you go, that is carrying capacity.3113

It can be exceeded but not for long.3114

Reproductive patterns, in terms of how different species become successful as an organism, there are two main strategies.3121

The life history patterns vary, in terms of how long they are alive, how many organisms they produce,3131

how quick do they have this turnover in generations.3138

There are advantage and disadvantage to both.3142

We have R strategists or K strategists.3144

Sometimes, you will see the term R selection or K selection, they are both the same term3148

but just depends on the source you are looking up.3154

If you are wondering what is the R and K stand for, what the heck?3157

They are these statistical population growth equations that relate to economics that relate to biology.3161

There is an R and a K variable in these particular formulas, I’m not going to write down for you.3170

But, that is what inspired these terms.3178

The way that I remember it is, it is always r and K, when you see these described.3180

The r means little organism and K bigger organisms, typically.3187

You can remember that we, humans, are K strategists or K selected.3195

You can think that we are okay, however you can remember it.3201

Let us discuss what is going on here.3208

R selection, here are some examples.3210

Bacteria, most insects, and rodents, are the r strategists.3212

Here is what true of them, they typically are smaller in size, that is true with these compared to other organisms.3219

Early maturity, how long an insect needs to be alive, or a rat need to be alive to make babies,3225

not that long compared to like a human or a monkey, very short amount of time that it takes for them to get to the maturity level.3234

They typically have shorter lifespan.3245

High fecundity, this is probably a new word.3248

Fecundity actually relates to this down here.3252

If you compare r selection and K selection, it is really opposites.3254

Down here, you see how I wrote offspring, high fecundity means a lot of offspring.3259

Fecundity is like amount of babies, in terms of the potential for making offspring.3266

Organisms like a rodent or a fly, it can make a lot of babies, a spider can make a lot of babies, that is a high fecundity.3283

Short lifespan, I mentioned that earlier, low paternal care, in terms of them actually caring for their offspring, usually it is not all.3295

Like when spiders hatch, they just go, bye and enjoy life, and they will rely on their instinct.3304

It is not that the mother is looking after them or raising them, or training them and teaching them things.3311

No, the mother will certainly guard those eggs before they hatch.3317

But once they hatch, goodbye.3323

This might seem like that is not as good as how we do it.3326

We are used to what we do, we are humans and we do what we do.3330

But, r selection has its advantages.3334

For the amount of years or sometimes days or months that they are on earth, they get it done quickly.3338

They mature quickly, they make a lot of babies, they are going to be the kind of organism where,3348

if there is a change in the environment, having a lot of babies just maximizes the chances that3356

maybe just one will survive or maybe a few will survive.3362

Because if you make 200 babies, it does not mean that all 200 are going to live to maturity.3365

The advantage there is that, in terms of the stressors in the environment, they are making a lot of babies,3374

and hopes some of them will be successful and they will go on to make hundreds or thousands of babies.3379

Part of this is, without r selection, without these organisms, you would not have K selection organisms being successful.3386

Because a lot of K selection organisms depend on the r selected or r strategists, in terms of the food chain.3393

These, usually being small organisms are typically lower in the food chain, in terms of the kind of consumer they are.3401

There are advantages to this and they are definitely advantages to being a K strategist or K selected organisms.3410

Elephants, whales, humans, typically they are larger in size.3417

Late maturity, it takes more years for them to develop, in terms whether they are ready to engage in sexual reproduction.3423

Fewer offspring, sometimes there are just 1 or 2 reproductions, or will be every few years.3431

Organisms like ourselves, as we age, it is harder to make offspring.3440

Long lifespan, typically, and high paternal care.3446

In every respect of this, it is the opposite of r selected or r strategy.3450

High paternal care, you see that with elephants, you see that with what is called humans.3456

There are apes that actually will care for their offspring for like 7 years, that is a long percentage of an ape’s lifespan.3461

They are showing them the ropes, they are showing them how it is done and3471

maximizing their chance for going out there and being successful.3476

Considering they are having fewer offspring, that is important.3479

If you are going to have few offspring, you want to do everything you can to make sure that3483

they are going to make it because you are not producing many babies.3487

I have this organism here because a lot of birds are not quite K selection.3491

There are birds and this is one of them.3499

It is an interesting example, it is known as the arctic tern.3503

The arctic tern actually really does raise its babies for a long period of time.3513

You will see it with its babies teaching them, actually teaching them what to do.3522

There are other bird examples too, it is not just mammals that are K strategists.3528

You will see ducklings walking around with their mom, and that is another example of K selecting.3534

Density factors, these are factors affecting population growth.3544

Sometimes, these factors, depending on the density, depending on the number of organisms in that habitat,3550

they become more of an effect or more of a factor.3556

There are other factors that are density independent meaning regardless of how dense the population gets, it is the same either way.3560

Here is what I mean, first let us start with the density dependent factors.3567

These get more intense, in terms of their effect, as the population gets more dense.3571

With an increase in density, you therefore get increase in its effect or how quickly it kind of spreads,3579

in terms of impacting these organisms.3600

Let us think about this disease, the closer quarters or the closer in proximity that animals get,3603

the quicker a virus or bacterial infection can hop from organism to organism.3612

Imagine a densely populated area of humans, and somebody has tuberculosis and they are coughing a lot.3617

They are coughing on people that are very close to them.3626

Those people are more likely to get tuberculosis and then spread it to people near them.3628

But if you think of a very rural area where there are thousands of yards between houses,3632

it is less likely for disease to spread quickly through that kind of scenario,3641

because it is not as dense in terms of the population density.3645

Disease like a viral infection or bacterial infection can actually have a big impact the more dense the population is.3650

Different kinds of competition, the competition for food, the competition for space,3658

it is more enhanced as the population density increases.3665

Predation, if you consider predators in terms of going after prey, if there is a lot of prey around,3669

that is going to affect the predation rate, if you want to think of it that way.3678

Parasites like this one, like a tick or a louse.3683

By the way, a louse is singular for lice.3689

A lot of people do not know that, that lice that end up in your hair, one of them is called a louse.3697

The kinds of insects that just bite at your skin and suck your blood.3703

Also internal parasites, the more organisms you have in a densely populated area,3710

the easier they are going to be able to hop around and infest those organisms.3718

Food availability, this is also related to competition.3721

It makes sense that the amount of food, the more organisms that are there,3726

the quicker that that food availability is probably going to just drop.3730

Those are density dependent factors, they do depend on the density level of organisms.3734

You have density independent factors, this means that as density increases or you have a decrease in density, same effect.3740

Effect with an E is the event or the result, affect with an A is the action affecting you.3769

Increase in density, decrease in density, has the same effect regardless.3777

Here is why, temperature, regardless of how many organisms are in an area, the atmosphere temperature is what it is.3782

If you are in a desert, the desert is going to be hot, regardless of how many cacti are there.3790

Regardless of how many kangaroo rats which you are going to find in desert population in certain areas.3795

Natural disasters like a tornado or a flood or an earthquake, it does not matter how many organisms there are,3802

it is going to have an equally devastating effect on that population or on that community.3809

Rainfall, regardless of how many organisms are there, the rainfall is what is.3814

Same with drought, the lack of rain.3819

Pesticides, pesticides which are meant to control the amount of insects feeding on plants or on crops.3823

Regardless of how many plants are there, it is going to have an equal impact on the soil and other organisms.3832

Predator/ prey relationships, in terms of the numbers of predators and the number of prey over time,3841

they have an impact on one another.3849

You want there to be a balance, if you have too many predators, the prey can drop too low.3851

If you have too many prey then they might be eating too many of the plant life in the area,3858

that can have an impact on the predator’s success.3865

It is this balance, here is what I mean.3868

If you consider the number of lynxes and number of hares in the population over 100 years time,3871

a lynx if you are unaware is kind of like a bobcat, different species, but it looks like a bobcat.3877

And a hare, it is a kind of rabbit, typically with pretty big ears.3883

Here on the Y axis, we have the number of organisms.3889

The exact numbers do not matter, this is just a good example of how a predator/ prey relationships impact one another,3894

in terms of the numbers.3900

Over 100 years time, we are seeing numerous generations of both the prey which is the hare,3902

they are being eaten by the lynx, the predators.3910

You can see that in general, you are typically going to have more prey than the predators.3913

The red lines corresponding to this relative of the rabbit is typically greater.3920

That should not be a surprise because when we look at the numbers pyramid,3925

you typically have more plants than the organisms that are eating plants like a hare.3931

You have more hares than organisms that are eating them, and so on.3936

But, you can see that every time you get a drop in the hare population,3939

you typically have a drop in the lynx population nearly afterwards.3945

Why, if you have less hares, less rabbits like here, the rabbit population drops, you have less food for the lynx.3949

The rabbit population drops, you then have a drop in the number of lynxes.3960

Eventually, you get a recovery of the hare population.3965

Let us think about the factors that could have had an impact on this.3969

Maybe, there was a disease, maybe too much hunting, maybe it was a drought and there was less plant life for the rabbits to depend up on.3972

Whatever it was, drop in the rabbit population, dropped significantly, right around looks like 38 or 40.3983

And then of course, the lynxes, they have less food to eat so they drop.3993

Inevitably, whatever rabbits were left, they make babies, the plant life returns, they have a lot of food.3998

And then, over this span of time, lot more rabbits.4007

The lynxes, over time, there are a lot of rabbits jumping around, food.4011

The lynx population starts to climb back up again.4018

If the rabbit population continues to climb here, we can assume that the blue problem would have continued to climb.4022

But for whatever reason, rabbit population drops followed by a lynx population drop.4029

You can see that they do impact each other overtime,4035

this is one of those classic examples of predator numbers versus prey numbers over time.4039

Thank you for watching