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  • A biome is a large region which has a certain, or typical, climate, animal life and vegetation.
  • Tropical forest biomes are located in equatorial regions. They have the largest animal diversity of any biome. Multiple levels, including canopy, shrub and herb layers are found in tropical forests.
  • Temperate broadleaf forests have cool to cold winters, and warm summers. They are characterized by broad leaf trees, typically deciduous, especially in the northern hemisphere.
  • Coniferous/Taiga biomes contain coniferous trees, which are resistant to damage by snow. Taiga is located between latitudes 38° to 45° north.
  • Deserts have low precipitation and are inhabited by drought resistant plants, including low shrubs and cacti. Many animals in desert biomes are nocturnal.
  • Grasslands include the savannas as well as the North American prairies. Plant life is adapted to tolerate fire and drought and primarily consists of grasses, along with some trees.
  • Tundra is characterized by cold, long winters and cool summers. There is a layer of permafrost below the surface. Herbs, grasses, small shrubs and lichen are found in this biome.


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  • Intro 0:00
  • Ecology 0:08
    • Ecology
    • Environment
    • Integrates
    • Environment Impacts
  • Population and Distribution 3:20
    • Population
    • Range
    • Potential Range
    • Abiotic
    • Biotic
  • Climate 7:55
    • Temperature
    • Precipitation
    • Wind
    • Sunlight
    • Macroclimates & Microclimates
  • Other Abiotic Factors 12:20
    • Geography
    • Water
    • Soil and Rocks
  • Sunlight 14:42
    • Sunlight
  • Seasons 15:43
    • June Solstice, December Solstice, March Equinox, and September Equinox
    • Tropics
    • Seasonability
  • Wind and Weather Patterns 20:44
    • Vertical Circulation
    • Surface Wind Patterns
  • Local Climate Effects 26:51
    • Local Climate Effects
  • Terrestrial Biomes 30:04
    • Biome
    • Forest
  • Tropical Forest 32:00
    • Tropical Forest
  • Temperate Broadleaf Forest 32:55
    • Temperate Broadleaf Forest
  • Coniferous/Taiga Forest 34:10
    • Coniferous/Taiga Forest
  • Desert 36:05
    • Desert
  • Grassland 37:45
    • Grassland
  • Tundra 40:09
    • Tundra
  • Freshwater Biomes 42:25
    • Freshwater Biomes: Zones
    • Eutrophic Lakes
    • Oligotrophic Lakes
    • Lakes Turnover
    • Rivers
    • Wetlands
    • Estuary
  • Marine Biomes 48:45
    • Marine Biomes: Zones
  • Example 1: Diversity of Life 52:18
  • Example 2: Marine Biome 53:08
  • Example 3: Season 54:20
  • Example 4: Biotic vs. Abiotic 55:54

Transcription: Biomes

Welcome to

Today, we are going to begin a series of lectures on ecology beginning with the topic of biomes.0002

Since, this is the first lecture on ecology, I am going to start out with a general introduction to the subject.0008

So, first of all, ecology is the study of the interaction of organisms with each other and with their environment.0014

The environment is the surroundings that affect an organism, population or community.0024

And in later lectures, we will talk about ecology on a population and community level.0053

Some examples of topics and questions that would be covered by the field of ecology are for example:0058

How does long term climate change affect a population of amphibians in the Central American mountains?0065

Or what is the impact of drought on the Ash-throated Flycatcher behavior in the Sonoran Desert?0072

or a study of the relationship between sea urchin populations and kelp growth.0080

Also, an ecologist might try to determine the possible impact of the use of a particular pesticide on the health of birds in an area.0086

So, as you can see, ecology is an extremely broad topic, and it is the integration of many areas of study.0097

Some of these areas that it integrates are the study of weather, climate, geology, animal behavior, which was discussed under a separate lecture,0105

evolutionary biology - again, that is a set of separate lectures in this course - natural history and others.0121

Environmental impacts are a key area of study in the field of ecology,0142

topics such as climate change, air and water pollution, land use, water use, eutrophication and others.0155

So, we are going to start out now with definitions and then, go on and talk about factors such as climates,0181

geological features that can affect populations and then, talk about various biomes and their characteristics.0192

A population is a group of organisms from a particular species that is found within one physical area.0202

And these organisms have the ability to breed and to interact.0212

The range is the geographic or physical area in which is a species is located.0220

Now, a population of a species may or may not be present in a particular location due to a variety of factors.0229

And we are going to examine some of these factors today.0239

In some cases, a species is not present, but it has the potential to live in that location.0245

That location has the right climate and food sources and other things to support the species.0250

But, the species may not be there for example because of geographic limitations.0256

A land mammal cannot cross a large ocean, or it will be extremely difficult.0262

So, that geographic barrier of a large body of water might prevent that mammal from settling in this new area.0269

Or it may be possible for an animal, a species, to travel over a body of water, but it just has not happened yet.0278

Birds and insects are actively and constantly populating new areas.0286

So, there is range, which is the actual area, so the range or actual range of a species is the area it is located in.0291

However, there is also the potential range, and these are locations with conditions that are favorable to a species.0308

So, if a species were to end up in that area, it could live there, but it is not there yet, so actual range versus potential range.0330

And various factors cause a particular species to be present or allow it to survive there.0340

And these can be classed into two broad categories: abiotic factors and biotic factors.0346

Abiotic factors are non-living. These are non-living physical features, chemicals that are present or events that occur.0353

And we are going to be discussing these various factors throughout this lecture.0374

Biotic factors that can affect a species range, so biotic are biological features, so biotic are living or biological factors that can influence a population's range.0379

So, it is the influence of one organism on another organism or on an ecosystem, for example, a predator would affect a prey in a particular environment.0397

The availability of food, if there is a type of plant in an area that an animal feeds on, that will affect the ability of that population to settle there.0422

Disease: if there is a fungal infection present, that can decrease or prevent a population from settling in a certain area, so these would be biotic factors.0430

I mentioned the word ecosystem just now, and so I am going to go ahead and define that.0441

This is the combination of all of the organisms, geology, geography, water, light, weather, climate, so this is all the abiotic and biotic factors in a given area.0446

We are going to start out by talking about climate first, so some abiotic factors here.0469

Climate describes a region in terms of factors like temperature, precipitation, wind and sunlight over the long term.0477

And I want to note that this is different than weather.0486

Weather describes the conditions of the moment. It is short term.0489

So, It can be raining outside, but that does not mean that it is a wet climate overall.0493

Climate has a profound effect on the species of animals that can live in a location- affects species ability to live in a location.0498

We will discuss some of these major factors now beginning with temperature.0518

Most proteins break down at about 45°C. At 0°C, water freezes and cells can rupture.0524

Organisms have an ideal temperature depending on a particular organism, and the range of temperatures that an organism can tolerate varies.0546

Some organisms can survive large variations. It is not just the absolute temperature, it is variations.0557

Some animals can survive large variations, large swings in temperatures. Others need a stable environment in terms of temperature.0566

Also, the extremes: some organisms are very sensitive to higher or lower temperatures.0573

On the other end, we have the extremophiles that can survive high temperatures or other extreme factors.0582

Some examples: reptiles require relatively warm temperatures, while mammals have a wider range.0589

They are endothermic and can maintain their body temperature more easily.0597

Precipitation is a second major factor in climate.0603

Precipitation provides water. It also determines the availability and type of surface water.0607

So, that is clearly going to affect the species of animals and plants, so animals and plants that can settle in a region and the same with temperature.0620

I was focusing on animals, but, of course, temperature is going to affect the type of plants that can live in a region.0631

Wind: wind spreads seeds. It can do things like influence bird migration.0638

It also affects the soil. It affects plant growth, tree growth.0647

Sunlight: sunlight is another factor in a climate, and of course, sunlight is required for photosynthesis. However, sunlight also damages DNA.0657

When we talk about aquatic biomes, I am going to discuss that water absorbs the sunlight.0672

What life survives at the various depths of water depends in part by the amount of sunlight at that depth.0683

We can look at climates in terms of macroclimates, very large regions, the global climate or a regional climate.0692

We could say "OK, the south-western U.S.", local climate in a particular area near the ocean, for example.0703

We can take this down to an even smaller level and look at microclimates.0716

Literally, a very small area, like the forest floor, is going to have a different climate than outside the forest a mile away or something.0720

Even smaller, looking under a rock, because it is going to be cooler and moister under a rock.0729

There is a different climate there than just a foot away outside in the sun.0734

Other abiotic factors in an ecosystem also affect the distribution of species.0741

One of these is the geography of a region. Are there steep slopes?0749

Only certain plants and animals can survive on a steep side of a mountain.0756

Surface water: how much water is available? Where is it located?0761

The size of an ecosystem: is it a small island, a large land mass, a narrow isthmus?0770

Isolation: is it an island way out distant from other islands?0779

Elevation: elevation has an influence on climate. Higher up, there is going to be more ultraviolet radiation, greater winds, lower temperatures.0785

OK, so, geography is an abiotic factor.0795

A second one that I already mentioned when we go into a little more detail is water.0797

What are the characteristics of the water? It is salinity, the pH, the temperature.0802

How about the flow of the water, is it slow or fast moving? Is there a tidal action in the water.0810

What is the availability and reliability of surface water and ground water?0819

Other abiotic factors, soil and rocks, if you look at the mineral composition of the soil and the pH, that is going to determine in part the availability of nutrients.0832

Physical structure of the soil can determine the growth of plant roots, the ability of animals to burrow.0850

The chemistry of soil and rock also influences the chemistry of the water, of the ground and surface water. Chemistry of soil and rock affects the water.0861

So, you can see how all of the features of a system affect other features, both living and non-living.0871

Sunlight is a primary driver of climate in weather. Plants and by extension other life depend on sunlight for energy.0884

Now, latitude determines the intensity of sunlight, and this is because at higher latitudes, the surface is always at an angle to the incoming sunlight.0893

So, this would be an example of a higher latitude.0903

The same amount of sunlight reaching the ground is spread over a larger area at higher latitudes, and that is what this shows versus closer to the equator.0910

So, this is higher latitude. This is closer to the equator.0921

And because the sunlight is coming at an angle, it is spread all over a larger surface area than sun that is hitting the ground more directly.0926

Because of that, there is a major effect on climate caused by sunlight.0936

Seasons are also important in an ecosystem.0945

Is there variability between the seasons? How long of a growing season is there?0949

It could be very long in one area and very shorter almost non-existent in another area.0956

So, to understand seasons, we just have to go back and look at some basics.0961

And recall that the earth's axis of rotation is tilted at 23.5° relative to the sun.0966

Now, at June solstice, and I just want to note that in the northern hemisphere, June solstice is often just called summer solstice.0974

And the December solstice is often the winter solstice, called the winter solstice.0986

OK, at June solstice, as you can see here, the North Pole is tilted towards the sun. At December solstice, the South Pole is tilted towards the sun.0994

At March equinox and September equinox, so spring and autumn equinox in the Northern hemisphere,1012

the axis of rotation is neither towards or away the direction of the incoming sunlight.1020

Therefore, at March and autumn equinox, the sun is directly overhead at the equator at noon,1029

And all parts of the earth receive 12 hours of light and 12 hours of dark.1040

So, here, sun is directly overhead at the equator at noon.1051

And when we talk about biomes, we will talk more about the different types of season in these various biomes.1060

So, if we look now again at summer solstice or June solstice, on approximately June 21st,1067

sunlight is directly overhead at noon at 23.5° North latitude.1077

However, anything south of the Antarctic Circle is completely dark.1092

So, obviously, a situation where there is complete darkness, where there is little or no hours of daylight is going to have a major effect on an ecosystem.1098

Now, looking at the northern hemisphere during December or winter solstice,1108

at approximately December 21st, sunlight is directly overhead at 23.5° South.1115

Anything north of the Arctic Circle is dark for 24 hours.1136

The tropics receive the most sunlight and have the least seasonal variation. Therefore, the tropics are warmer, whereas, the higher latitudes are cooler.1141

So, the tropics tend to be warmer. The higher latitudes are cooler.1168

Seasonality: to give you an overview before we get to specific biomes, there are strong seasonal variations in the mid to high latitudes.1180

Whereas as I said, closer to the equator, there is little seasonal variation, and some plants and animals do OK with variation.1204

They can survive if being very cold at one time and very hot at another, whereas, other plants and animals cannot tolerate a lot of variation.1216

Around 20° latitude, there are regions that often have a rainy season and then, a dry season versus other1225

areas that may have rain intermittently more spread out throughout the year, not a distinct rainy and dry season.1238

We are now going to discuss some global patterns of wind movement and their effect on the weather.1245

Vertical circulation is the first topic. Near the equator, there is intense solar radiation that causes air near the surface to warm and rise.1253

The warm air also picks up moisture from the earth surface, and this moisture is released as the air rises.1294

As this air rises, it becomes part of a vertical circulation, and I am going to explain what I mean by vertical circulation.1325

So, just to recap, near the equator, the solar radiation causes air near the surface to warm and to rise.1339

As it rises, this warm air picks up moisture, and this moisture gets released as the air rises. This rising air becomes part of the vertical circulation.1351

One, what happens is as the air travels towards the poles releasing moisture as it cools. Then, it descends.1365

The air, it travels towards the pole releasing moisture as it is cooling down, as it is rising up.1392

Then, it descends towards the surface at around 30° latitude. At that point, the air is now relatively dry.1399

So, the air has risen up. It is releasing moisture, and it is cooling.1416

And then, it descends towards the surface of the earth around 30° latitude, and it is descending; and it is fairly dry at that point.1422

So, then, the air reaches the surface, recirculates towards the equator and then, repeats the cycle.1429

The same general pattern of vertical circulation repeats two more times.1450

So, it repeats again between latitudes 30° and 60° latitude and then, between 60° latitude and the poles.1460

So this rising and then, releasing the moisture, descending, picking up moisture, this repeats several times from the equator and then,1481

at 30° between 30 and 60 and then, again, between 60 and the poles.1491

Now, this is going to have an effect, then, at the temperature - excuse me - of the climate depending on what is happening with the circulation pattern.1499

At the equator, the Earth's surface is moving faster than it is towards the poles.1512

This creates a shear in the air mass and circulation patterns that encircle the entire globe.1519

So, global patterns of wind influenced by the fact that at the equator, the earth's surface is moving faster than it is toward the poles.1525

So, this is creating an air circulation pattern, and the air flow pattern is generally east to west air flow near1551

the equator and west to east in the middle latitudes or what is sometimes called temperate zones.1562

Now, these surface wind patterns together with vertical circulation define typical weather throughout the world.1583

We talked about sunlight as having a major influence on weather.1595

Also, these global patterns of vertical circulation and surface airflow all influence the various climates in regions throughout the world.1599

Now, we looked at broad patterns but, there are also local climate effects.1612

So, you might be living in a hot climate, a really hot dry climate, and then, you go down to the beach, and it is much cooler and moister.1616

Or you go up in the mountains, and it is a lot cooler up there.1625

And that may not even be very far away from where you are living in what is generally a hot dry climate.1627

So, climates vary locally, and this can result in different populations of animals and plants, for example, up in the mountain versus just below in a valley.1632

Some major features that can affect local climates are mountains.1645

And here is an example of the windward side of the Sierra Nevada versus the leeward side.1649

So, on the windward side, as air passes over the mountains and rises, moisture is released.1654

And you can see it is a lot greener, a lot more growth here. So, on the windward side, air passes over mountain and releases moisture.1661

So, this is going to result in a local climate that is much wetter, more rain fall, relative to the leeward side of the mountain,1677

on the leeward side and regions down when the mountain are going to be relatively dry.1693

This is sometimes called the rain shadow effect. You will see this not only in the Sierra Nevada’s, but another good example is in Hawaii.1700

Alright, so mountains can have an effect on the local climate. Large bodies of water can also have effects on local climate.1715

For example if you look at lakes and oceans, regions downwind of these large bodies of water receive1723

more precipitation due to moisture that is picked up by the air mass as it passes over the water.1730

Looking at the Pacific Northwest gets a lot of rainfall for these reasons, areas east of the Great Lakes in the United States, also the Gulf Coast of the U.S.1737

So, oceans: in addition to these examples where being near body of water causes more precipitation,1750

areas that are adjacent or downwind of oceans tend to have a moderate climate, and this is due to the moderating effect of the ocean.1758

The relatively constant ocean temperatures have a moderating effect on nearby areas.1773

And if you go back and watch those lectures on the properties of water,1778

you will understand how a large body of water can affect temperature and patterns in the land nearby, as well.1782

Now that we have talked about factors like sunlight, seasonality, wind, geographic features, we are going to talk about various biomes.1794

And these are important for you to know for the exam.1803

So, a biome is a large region that has a particular or what we call typical climate, animal life and vegetation.1806

You may hear the term biosphere as well, and this is the global ecosystem.1816

So, when we take the entire planet as a whole and look at it as an ecosystem, that is the biosphere.1822

We can, then, divide that up into large regions but not including the whole earth as biomes.1830

There are various classification methods for biomes. Generally though, they are arranged by climate.1837

The boundaries from one biome to another are gradual.1844

I am going to show you maps that are going to show desert biome versus taiga or tundra and all these different biomes.1847

But, there are not sharp demarcations. They can sometimes just blend very gradually one into the other.1856

Starting out talking about forest biomes, in general, forest biomes have moderate to heavy precipitation.1864

We are going to talk about a few different types of forest biomes, but just very generally, 70 to over 200 centimeters of rain fall per year.1880

They often have large trees and multiple layers. These layers are also called strata and a large animal...1891

Features: moderate to heavy precipitation, large trees with multiple layers and also, a large animal population.1905

Birds, large and small mammals, insects, various other organisms, and we are going to look first at tropical forest.1914

These are equatorial regions, and you can see here on this map, this shows the location of tropical forests.1925

And you will see that these are located near the equator. They have the largest animal diversity of any biome.1933

There are millions of insects species here. There are also many species that have not even yet been discovered.1947

There are reptiles and amphibians in addition to various birds and mammals, and there are multiple tree layers including a canopy.1954

So, there is this overlying canopy, and then, lower down, there are shrub layers and then, herb layers.1966

A second type of forest biome is the temperate broadly forest, and this is found, as you can see from this map, at the mid-latitudes.1977

Temperate broadly forests have cool to cold winters and warm summers.1988

And you can see that much of the eastern coast is the United States, and large regions of Europe have temperate broadly forest.1998

They have broadly trees, and these are typically deciduous trees that lose their leaves in the winter especially in the northern hemisphere.2013

Animals in temperate broadly forest may hibernate, and here, you can see an example of a broadly forest in the autumn when the trees are changing.2034

Coniferous or taiga forest are the next type we are going to cover, and I just want to talk a little bit about classification.2053

Some classification schemes say that the broad name or the broad classification is coniferous and that taiga are subset of that.2060

Others classify coniferous as one type and taiga as another, so you are going to see different classifications schemes.2068

I have put them together here, but I am going to mention the specific definition of taiga that is often used.2074

So, some examples of coniferous forest are the Coniferous Montane Forest.2080

These are forests that are found in the European Alps, so shown here, as well as the Rocky Mountains in the U.S.2089

Its name tells you and this picture shows you that coniferous trees are found here.2106

These are trees that are not damaged by snow. They also have less vegetation in the lower layers, this type of forest does.2111

As far as animals, there are often many large mammals found here such as bears, moose, wolves.2121

Taiga are coniferous forests that are found between latitudes 38 and 45° north.2133

Taiga is the largest biome, and it is characterized by cold winters and mild summers. Much of Canada, in fact, most of Canada is taiga.2144

Deserts have low precipitation. They are not necessarily hot, but they are typically variable.2167

So, the difference between, let's say, the day time and night time temperatures can be big or summer versus winter especially night time temperatures.2177

And they are typically found around 30° latitude.2185

They are also found on the interior areas of continents that are not necessarily at 30° latitude.2191

But, interior areas of continents may also have some deserts even though other parts of that continent are not desert climate.2202

As far as plant life, what you will often see in deserts, which you can see right here, is that there are low shrubs and cacti.2216

These are drought-resistant plants that have a minimal leaf area to conserve water.2224

Animal life: typically, reptiles are found here, rodents, small mammals, birds, insects and many of the animals that live in a desert biome are nocturnal.2240

Grasslands are temperate climates. An example of a grassland is temperate grassland.2268

Let me correct that- temperate, for example the North American Prairie, the Russian Steppes, as well as the South American Pampas.2279

These temperate grasslands have warm summers and cold winters.2312

The Savannahs can see it right here is where the Savannahs would be located or larger.2324

But, Savannahs are equatorial grasslands, and these have a warm climate year round.2333

So, even within one type of biome, there are subdivisions. There are differences.2345

Grasslands, as the name suggests, are mostly grass. There are some trees, and the plant life is adapted for fire and drought.2353

So, plant life, mostly grass, some trees, and these are adapted to survive periods of fire that come through and drought.2362

As far as animals, often in a grassland, what you will find is large grazing animals, large grazing mammals,2380

for example, elk, bison, zebra, also the predators of these mammals.2392

Burrowing rodents are often found in grasslands, as well.2400

The final terrestrial biome that we are going to cover is tundra.2406

Tundra is found at high latitudes and also found at higher elevations in mountains of all region, so high latitudes.2411

And there are other regions that have tundra that might be some mountains that are in the middle of another type of biome.2424

But if you go up to a high latitude in the mountain, what you will see is tundra sometimes and higher elevations of mountains in all regions.2430

Tundra is characterized by cold long winters and cool summers. One subtype of tundra is called alpine tundra.2448

An example would be the Himalayas and other mountains greater than 2000-4000 meters in height, so that is just a subtype of tundra.2467

Plant life: what you will typically see in tundra are herbs, grasses, smaller shrubs and lichen.2490

There is a layer of permafrost below the surface.2508

And grazing migrating large mammals such as elk and deer live on the tundra as well as their predators, predators like bears and wolves.2512

There are some rodents and also migrating birds.2531

So, we covered the terrestrial biomes. Now, we are going to talk about some aquatic biomes starting with freshwater biomes.2540

Aquatic biomes are often divided into zones, so what is shown here would be a freshwater lake for example.2548

And if you look at the lake in terms of zones relative to the distance from the shore, the littoral zone is the zone that is near the shore.2557

The limnetic zone is distant from the shore to the point where there are no rooting plants.2569

Whereas, the littoral zone could have plants that are rooted in the shore.2580

There is also in the limnetic zone, there is no shade or other influence from onshore vegetation.2583

You can also divide zones of a lake according to light, and that is what photic and aphotic has to do with.2591

Photic zones are the upper zones, and they receive light, so this area is limnetic and is also photic because if you are looking at the top part.2597

Whereas, if you are looking distant from the shore but deeper, it is going to be aphotic.2609

So, it is different characteristics that you are classifying it based on.2615

Photic means that it receives light because remember the water absorbs the sunlight,2619

so as you go deeper, you would enter the aphotic zone where there is little or no light.2624

The floor or bottom of a body of water is called the benthic zone. This is the floor.2633

Pelagic is out in the open water.2644

So, we have near shore, littoral, distant from shore, limnetic, receives light, photic, little to no light is aphotic.2648

The floor is the benthic zone, and pelagic zone is out in the open water.2657

Lakes can be categorized as eutrophic or oligotrophic.2667

Eutrophic lakes are nutrient-rich but oxygen-poor.2675

These are usually relatively shallow, and they are nutrient rich because they have decomposing organic matter in their sediment; so that is eutrophic.2686

Oligotrophic lakes are nutrient-poor but tend to be oxygen-rich. An example would be alpine lakes would be oligotrophic.2703

Type of life that is found in lakes: fish, invertebrates, various heterotrophs or the2724

heterotrophs that could be found floating and rooted plants in the shallow areas.2731

In deeper areas, phytoplankton is also found.2737

There is a stratification that can occur of the water especially in summer and winter, and the result is that there is low oxygen at the bottom.2741

There can also be a thermal gradient in a lake, and this is called a thermocline.2751

In lakes, often, the water becomes mixed in the summer and in the autumn.2766

So, this is called the turnover, the lakes turnover and both spring and autumn, so spring turnover and then again in the autumn.2771

What this does is it brings oxygen to the lower depths.2789

And it brings nutrients to the surface, so it brings oxygen.2797

It is going to descend, and then, the nutrients can ascend.2804

Rivers: so, a key point with rivers is that the chemistry can change if you move from the headwater to the mouth of the river.2814

So, from the origin of the river the headwater is to the mouth.2827

It is often starts out at the headwaters being a high oxygen, low solids and faster moving, and this is at the headwaters.2834

And then, as it proceeds, it changes, becomes lower in oxygen, increased organic matter and increased nutrients, and the water is typically slower-moving.2848

You should be all familiar with the term wetlands. Wetlands are land that is partially or intermittently inundated by water.2863

These wetlands are usually freshwater. They can be saltwater near the ocean, though.2884

They are nutrient-rich and have high organic production.2889

Estuaries: an estuary is a zone where freshwater meets the ocean.2894

So, an estuary is intermittently fresh versus salt water depending on the tides, and in an estuary, you will find life such as shellfish, worms and birds.2905

So, these are freshwater biomes. Although, as I said, estuary is a mix, but now, we are going to focus exclusively on marine biomes.2917

The definition of these various zones is pretty similar to freshwater. There are some slight differences.2927

For example, the region at the shore is intertidal, and the intertidal zone is intermittently submerged with waves.2933

And it is also depends on the tide- high tide versus low tide.2942

Neritic means near the shore, whereas, oceanic is away from the shore.2945

The same terminology we talked about with the freshwater zones is used here in terms of light:2955

photic zone- towards the surface, receives light; the aphotic zone- deeper down, receives little or no light.2961

As with freshwater, benthic means the bottom or floor of the ocean. Pelagic is open water.2973

And there is another term here just for marine biomes, which is abyssal, and these are areas that are deeper than 2000 meters.2983

Intertidal zone, as I said, it varies. It can be continuously submerged or occasionally submerged.2993

It depends on the structure and the features of the tides and things, but there are a lot of variations in intertidal zones.3000

They can be rocky or sandy, oxygen and nutrient-rich, and they support shellfish, worms, crabs and various other ocean life.3010

Out in the pelagic zone, that is open water, so oxygen levels are high. but nutrient levels are low.3019

There are phytoplankton found there including photosynthetic bacteria, zooplankton, worms, krill, larva many other animals consume phytoplankton.3026

There are also fish, squid and various marine mammals out in the open water.3037

Coral reefs, which have come up in various places in course, but again, these are formed from the skeletons of coral organisms.3043

They are high in oxygen but relatively low in nutrients.3060

The benthic zone often gets little or no sunlight.3067

In shallower areas of the benthic zone where there is light, you can get photosynthetic organisms like sea weed.3074

Near hydrothermal vents, there are organisms that I also discussed earlier in the course, so near hydrothermal vents.3082

There are organisms that use hydrogen sulfide for energy.3094

But, otherwise, deeper areas really just depend on nutrient-rich material settling down from above, from the shore in marine biomes.3102

OK, today, we have covered a variety of topics specifically focusing on biomes.3114

We are going to go ahead and review these, starting with example one.3120

Which location would be expected to have the greatest diversity of life forms?3123

Under which biome would it be classified: a forest in the mountains of Southwest Canada, the grassy plains of Southern Africa,3128

a forest in Central Brazil, forested areas of Western Europe or the deserts of Central Australia?3138

Well, I would expect the greatest diversity in a tropical rainforest, and in fact, a forest in Central Brazil would meet this definition.3147

So, the answer is C, and this would be classified as tropical rainforest.3155

Fill in the boxes with the proper terms for the zones in a marine biome.3165

Alright, we just discussed this, and this area that is alternately submerged and revealed over at the shore is known as the intertidal zone.3170

Near the shore is the neritic zone. Right here, what you see is right by the ocean floor and this is, therefore, the benthic zone.3184

Now, this can be classified a couple of ways. If you look distant from the shore, it is oceanic zone.3199

And if you look out in the open water, it is the pelagic zone.3209

I do want to note though that these more shallow areas you could have also classified as photic, and that would have been correct.3213

And then, the deeper area, because this would be also photic zone, you could have classified as aphotic. This did not specify.3220

But, if you are talking about in terms of distance from shore versus open water versus light or little to no light, you could classify them both ways.3229

So, intertidal, then, near the shore- neritic, distant- oceanic, open water- pelagic zone. Benthic is at the floor.3239

And then, photic versus aphotic closer to the surface is going to be photic and receive light. Deeper down, aphotic little to no light will reach those regions.3250

Example three: when would a newly sprouted seedling of a particular species of grass in3260

the North Central United States have a greater growth rate, mid-June or mid-September?3267

Explain and assume the same temperature and precipitation, so at both times, we are not going to worry about variations in temperature and precipitation.3274

Now, greater growth would be expected to occur in the northern hemisphere in mid-June.3284

And that is because in mid-June, there is going to be over 12 hours of sunlight.3293

Also, in June, the sun is going to be at a higher angle than in September in the northern hemisphere.3304

This higher angle means that there will be more sunlight per area on a leaf.3310

So, I would expect the growth rate to be faster in mid-June than in mid-September.3316

Example four: indicate whether each item in the list below is a biotic factor or an abiotic factor.3323

Remember that biotic factors are living, whereas, abiotic factors are non-living, so if we look at elevation, how would that affect an ecosystem?3330

Well, elevation is not living, so that is an abiotic factor. The density of phytoplankton, living organism, so it is biotic.3343

pH of lake water, non-living, so it is abiotic, and intestinal parasite, biotic because it is living.3354

Atmospheric carbon dioxide content, non-living, abiotic, and the introduction of an exotic species to an island- biotic.3367

Now, when this comes up, I want to note the idea of introduced species because this can have a profound effect on an ecosystem.3378

A classic example is the case of the brown tree snake in Guam. The brown tree snake was introduced accidentally to Guam in the 1940s.3386

It is believed that it came over in cargo holds of ships after World War II.3398

There are now estimated to be about two million of these snakes on the island of Guam.3404

And because it did not have natural predators, it really has caused a lot of problems.3410

And at least, ten species of birds have become extinct as well as five or more lizard species.3416

So, this is an example of the extreme effects that an introduced species can have because an introduced species may not have a natural predator.3421

And there is nothing then to keep its numbers under control.3432

That concludes this section on biomes here at

Thank you for visiting.3441