What do you call a collection of organisms that belong to different populations but all live in the same area and interact with one another?

Observe the cheetah hunting its prey. What is it called when one organism hunts another organism? Predation. Predation may not be good for the survival of an individual organism, but it is a very important part of life. This is because every interaction between an organism affects other organisms in an ecosystem.

What other things do you notice about the image? Where is the cheetah hunting? How do you think the cheetah has adapted to live in that particular environment? What do you think the weather is like? Does it rain a lot? Are there bigger trees? Or just small grasses?

All of the living and non-living things and how they interact with each other make up an ecosystem. The study of these interactions is called ecology. Ecologists ask questions like, "What would happen if the cheetahs' prey goes extinct?" and, "What would happen if a fire wiped out the grasslands where cheetahs live?"

Think about other interactions between organisms you have observed. Maybe you have seen a bee sucking the nectar out of a flower, or a cow grazing on grass. What habitats do these organisms live in? How do humans affect their habitats?

All of these questions are ecological questions. Think about them as you read the following chapter.

Introduction to Ecology

Lesson Objectives

• Define ecology.
• Describe how organisms can interact with their environments.
• Describe levels of organization in ecology.

Check Your Understanding

• What is an adaptation?
• What is the scientific method?

Vocabulary

• abiotic
• biome
• biosphere
• biotic
• community
• ecology
• ecosystem

What is Ecology?

Life Science can be studied at many different levels. You can study small things like molecules or cells. Or you can study big things like whole organisms or groups of organisms. The largest level that you can study is the level of ecology. Ecology is the study of how living organisms interact with each other and with their environment.

Because it is such a large field, ecology involves many different fields, including geology, soil science, geography, meteorology, genetics, chemistry, and physics. You can also divide ecology into the study of different organisms, such as animal ecology, plant ecology, insect ecology, and so on.

A biome is a large community of plants and animals that live in the same place. Ecologists can also study biomes. For example, ecologists can study the Arctic, the tropics, or the desert (Figure below). Can you think of different species or biomes that ecologists could study?

An example of a biome, the Atacama Desert, in Chile.

Ecologists do two types of research:

1. Field studies.
2. Laboratory studies.

Field studies involve collecting data outside in the natural world. An ecologist who completes a field study may travel to a tropical rain forest and count all of the insects that live in a certain area. Laboratory studies involve working inside, not in the natural world. Sometimes, ecologists collect data from the field, and then analyze it in the lab. Also, they use computer programs to predict what will happen to organisms in who live in a specific area. For example, they may make predictions about what happens to insects in the rainforest after a fire.

Organisms and Environments

All organisms have the ability to grow and reproduce. To grow and reproduce, organisms must get materials and energy from the environment.

An organism’s environment includes two types of factors:

1. Abiotic factors are the parts of the environment that have never been alive, such as sunlight, climate, soil, water and air.
2. Biotic factors are the parts of the environment that are alive, or were alive and then died, such as plants, animals, and their remains.

Biotic factors, like organisms, interact with abiotic factors. For example, all animals (biotic factors) breathe in oxygen (abiotic factor). All plants (biotic factor) absorb carbon dioxide (abiotic factor).

Can you think of another way that abiotic and biotic factors interact with each other?

Levels of Organization in Ecology

Ecology can be studied at small levels or at large levels. Levels of organization are described below from the largest to the smallest:

• The biosphere is the part of the planet that has living things on it (Figure below and Table below). This is most of Earth.
• An ecosystem is the living things in an area interacting with all of the abiotic parts of the environment (Figure below).
• A community are all of the populations of different species that live in the same area and interact with one another.
• A population is a group of organisms belonging to the same species that live in the same area and interact with one another.

The global biosphere, which includes all areas that contain life, from the sea to the atmosphere.

Satellite image of Australia

Ecologists study ecosystems at every level. They can ask different types of questions at each level. Examples of these questions are given in Table below, using the zebra as an example.

Lesson Summary

• Ecology is the scientific study of how living organisms interact with each other and with their environment.
• The study of ecology can be broken down into different fields and studied in the field or in the lab.
• An organism’s environment includes abiotic and biotic factors.
• Levels of organization in ecology include the population, community, ecosystem and biosphere.

Review Questions

Recall

1. Name three fields you can study when you study ecology.

2. Define ecosystem.

3. Define organism.

4. What are the four main levels of organization in ecology?

Apply Concepts

5. What is the difference between field studies and laboratory studies?

6. What is the difference between a population and a community?

7. Explain why almost the entire planet is a biosphere.

Critical Thinking

8. Give an example of how an abiotic factor can interact with the environment.

9. A question that an ecologist could ask at the population level is, “What factors control zebra populations?” Think of two examples of how other species may affect the zebra population.

Further Reading / Supplemental Links

Points to Consider

• What do you think causes populations to grow?
• What causes populations to decrease?

Populations

Lesson Objectives

• Define population.
• Describe how births, deaths and migration affect population size.
• Explain how populations grow.
• Describe how limiting factors affect population growth.
• Describe growth of the human population.

Check Your Understanding

• What is ecology?
• How does an organism interact with its environment?

Vocabulary

• birth rate
• carrying capacity
• death rate
• dispersion
• emigration
• immigration
• limiting factor
• population growth rate

What is a Population?

A population is a group of organisms of the same species, all living in the same area and interacting with each other. Since they live together in one area, members of the same species reproduce together. Ecologists who study populations figure out how healthy or stable the populations are. They also look at how the populations interact with the environment.

First, ecologists will measure the size of the population. The population density is the number of individuals of the same species in a particular area. Ecologists also look at how individuals in a population are spread across an environment. How individuals are spaced within a population is called dispersion. Some species may be clumped or clustered (Figure below) in an area. Others may be evenly spaced (Figure below). Still others may be spaced randomly within an area.

Individuals within this population of purple loosestrife plants are clumped because of the soil quality.

A population of cacti in the Sonoran Desert generally shows even dispersion due to competition for water.

Ecologists also study age and sex. The birth rate is the number of births per individual within a specific time period. The death rate is the number of deaths within a population during a specific time period. Knowing the birth and death rates of populations gives you information about a population’s health. For example, when a population is made up of mostly young organisms, it means that the population is growing.

A population with equal birth and death rates will have equal numbers of individuals at each age level. A population with more individuals at or above an age when they can reproduce means that the number of individuals is decreasing in the population. This is because the organisms in this population cannot reproduce any more, so more children cannot be born, and then the population cannot grow.

Births, Deaths, and Migration

Births, deaths and migration all affect population growth. The population growth rate tells you if the number of individuals in a population is increasing or decreasing. Population growth rate depends on birth rate and on death rate. You can predict the growth rate by using the simple equation below:

If the birth rate is larger than the death rate, then the population grows. If the death rate is larger than the birth rate, what will happen to the population? The population will go down. If the birth and death rates are equal, then the population will stay the same.

Factors that affect reproduction are:

1. Age at first reproduction.
2. How often an organisms reproduces.
3. The number of offspring.
4. Parental care.
5. How long an organisms is able to reproduce.
6. Death rate of offspring.

Organisms can use different strategies to increase their reproduction rate. Altricial organisms are helpless at birth and their parents give them a lot of care (Figure below), while precocial organisms can take care of themselves at birth and do not require help from their parents (Figure below). In order to reproduce as much as possible, they use very different strategies.

A hummingbird nest with young illustrates an altricial reproductive strategy, with a few small eggs, helpless and naked young, and intensive parental care.

The Canada goose shows a precocial reproductive strategy. It lays a large number of large eggs, producing well-developed young.

Migration

Migration is the movement of individual organisms into or out of a population. Migration affects population growth rate. There are two types of migration:

1. Immigration is the movement of individuals into a population from other areas. This increases the population growth rate.
2. Emigration is the movement of individuals out of a population. This decreases the population growth rate.

The earlier growth rate equation now looks like this:

One type of migration that you are probably familiar with is the migration of birds. Maybe you have heard that birds fly south for the winter. In the fall, birds fly thousands of miles to the south where is warmer. In the spring, they return to their homes. (Figure below).

Monarch butterflies also migrate from Mexico to the northern U.S. in the summer and back to Mexico in the winter. These types of migrations move entire populations from one location to another.

A flock of barnacle geese fly in formation during the autumn migration in Finland.

Population Growth

If a population is given unlimited amounts of food, moisture, and oxygen, and other environmental factors, it will show a type of growth called exponential growth. Exponential growth means that as a population grows larger, the growth rate increases. This is shown as the J-shaped curve in Figure below. You can see that the population grows slowly at first, but as time passes, growth occurs more and more rapidly.

Growth of populations according to exponential (or J-curve) growth model (left) and logistic (or S-curve) growth model (right)

In nature, organisms do not usually have ideal environments with unlimited food. In nature, there are limits. Sometimes, there will be a lot of food. Sometimes, a fire will wipe out all of the available nutrients. Sometimes a predator will kill many individuals in a population. How do you think these limits affect the way organisms grow?

Usually, populations first grow exponentially. But as populations increase, rates of growth slow down and slowly level off. This is shown as an S-shaped curve in Figure above, and is called logistic growth. Why do you think occurs?

Limiting Factors

Limiting factors are things in the environment that can lower the population growth rate. Limiting factors include a low food supply and lack of space. Limiting factors can lower birth rates, increase death rates, or lead to emigration.

When organisms face limiting factors, they show logistic type of growth (S-curve). Competition for resources like food and space cause the growth rate to stop increasing, so the population levels off. This flat line in growth is known as the carrying capacity. The carrying capacity is the maximum population size that can be supported in a particular area without destroying the habitat. Limiting factors determine what the carrying capacity is.

Food Supply as Limiting Factor

If there are 12 hamburgers at a lunch table and 24 people sit down at a lunch table, will everyone be able to eat? At first, maybe you will split hamburgers in half, but if more and more people keep coming to sit at the lunch table, you will not be able to feed everyone. This is what happens in nature. But in nature, organisms that cannot get food will die or find a new place to live.

In nature, when the population size is small, there is plenty of food for each individual. When there is plenty of food, organisms can reproduce, so the birth rate is high. As the population increases, the food supply decreases. When food decreases, organisms cannot reproduce as well, so the birth rates goes down. This will cause the population growth rate to decrease.

When the population decreases to a certain level where every individual can get enough food to eat, and the birth and death rates are stable, the population has reached its carrying capacity.

Other Limiting Factors

Other limiting factors include light, water, nutrients or minerals, oxygen, the ability of an ecosystem to recycle nutrients and/or waste, disease and/or parasites, temperature, space, and predation. Can you think of some other factors that limit populations?

Weather is also a limiting factor. For example, an individual Agave americana actually likes to grow when it is dry. Rainfall limits reproduction, which in turn limits growth rate. Can you think of some other factors like this?

Human activities can also limit the growth of populations. Such activities include use of pesticides, such as DDT, use of herbicides, and habitat destruction.

What kind of growth rate do you think humans follow? Are they growing exponentially (J-curve) or logistically (S-curve)?

Growth of the Human Population

There are two different beliefs about what type of growth the human population undergoes:

1. Neo-Malthusians believe that human population growth cannot continue without destroying the environment, and maybe humans themselves.
2. Cornucopians believe that the Earth can give humans a limitless amount of resources. They also believe that technology can solve problems caused by limited resources, such as lack of food.

Which do you think is correct?

Does human growth looks like the exponential (J-shaped) graph or the logistic (S-shaped) graph? We don’t know all the answers yet, but history gives us some clues. For example, if we look at worldwide human population growth from 10,000 BCE through today, our growth looks like exponential growth. It increases very slowly at first, but later grows at a faster rate. It also does not approach a carrying capacity (Figure below). So maybe humans show exponential growth.

Worldwide human population growth from 10,000 BCE through today

On the other hand, if you look at human population growth in specific countries, you may see a different pattern. On the level of a country, the history of human population growth can be divided into five stages, as described in Table below.

The United Nations and the U.S. Census Bureau predict that by 2050, the Earth will be populated by 9.4 billion people. Other estimates predict 10 to 11 billion.

The Cornucopians believe that a larger population is good for technology and innovation. The 5-stage model above predicts that when all countries are industrialized, the human population will eventually reach a carrying capacity. But many scientists and other Neo-Malthusians believe that humans have already gone over the Earth’s carrying capacity for resources and habitat. If this is true, then human overpopulation will lead to a lack of food, disease, or war. These things will cause the population of humans to crash, or cause humans to go extinct.

For additional information, see this 2010 video: http://whoknew.news.yahoo.com/?vid=21435088.

Which of the above theories makes sense to you? Why?

Lesson Summary

• A population is made of organisms belonging to the same species, all living in the same area and interacting with each other
• One measure of a population’s health is the dispersion of individuals within a population
• The population growth rate shows how the population size changes per population member per unit of time.
• Birth rate, death rate, and migration affect population growth rate.
• In an ideal environment, populations show exponential growth. In nature, limiting factors cause logistic growth.
• There are two major beliefs about human population growth. Neo-Malthusians believe that human population growth is limited, and that overpopulation could have serious consequences. Cornucopians believe that human population growth can continue because of natural resources and technology.

Review Questions

Recall

1. Name two ways ecologists know that a population is healthy.

2. Define Birth Rate.

3. Define Death Rate.

4. What is the equation that calculates growth rate in a population, include information on migration?

5. What are three factors that affect reproduction within a population?

Apply Concepts

6. How does a limiting factor such as food supply limit population size?

7. Give two examples of environmental crises that support the idea that our human population has already grown beyond the carrying capacity resulting in environmental degradation.

8. What is the difference between Neo-Malthusian beliefs and Cornucopian beliefs about human population growth?

Critical Thinking

9. In the altricial reproductive strategy used by robins and hummingbirds, the birds hatch helpless and naked. Parents spend little energy in just a few small eggs. It is important these offspring survive because there are not very many of them. What strategies might parents use to make sure their young survive?

10. In human history, major advances in technology caused our population to increase rapidly. What do you think these major advances were?

Further Reading / Supplemental Links

Points to Consider

• Now that you understand what makes up a population, what do you think makes up a community?
• You have learned about some of the factors that limit populations. What do you think are some interactions that affect the community?

Communities

Lesson Objectives

• Define community.
• Describe community interactions.
• Explain how competition affects the community.
• Describe predation and how it affects prey density.
• Explain what symbiosis is and give examples of different kinds of symbiosis.

Check Your Understanding

• What is a population?
• How do limited resources encourage competition?

Vocabulary

• camouflage
• character displacement
• commensalism
• competition
• competitive exclusion principle
• keystone species
• mutualism
• parasitism
• predation
• symbiosis

What is a Community?

From populations, we are moving to the next level of ecology: the community level. In a community, different species that live in the same area interact with each other. The term "community" can be used in different ways. You can study populations in different areas of during different time periods. For example, you may study the fish community in Lake Ontario. But you could also study fish in a lake during a particular time period, like after 1990.

Community Interactions

Community interactions can be either:

1. Intraspecific: Interactions between members of the same species.
2. Interspecific: Interactions between members of different species.

There are a number of different types of interactions, but we will look at three different types:

1. Competition.
2. Predation.
3. Symbiosis.

Competition

Competition occurs when organisms compete for limited resources, and the “fitness” of one individual is lowered by competing with another individual. The interaction can be between organisms of the same species (intraspecific) or different species (interspecific).

Intraspecific competition happens when members of the same species compete for the same resources. They can compete for food, nutrients, space, or light. For example, two trees may grow close together and compete for light. One may out-compete the other by growing taller to get more available light. The organism that is better adapted to that environment gets to survive. In this case, it is the taller tree.

Interspecific competition happens when individuals of different species share a limited resource in the same area. One species will have lowered reproductive success, growth, or survival. For example, cheetahs and lions feed on similar prey. If prey is limited, then lions may catch more prey than cheetahs. This will force the cheetahs to either leave the area or suffer a decrease in population.

Looking at different types of competition, ecologists developed the competitive exclusion principle. The principle states that species less suited to compete for resources will either adapt, move from the area, or die out. This is similar to what happens within a species. Evolutionary theory says that competition for resources within and between species plays an important role in natural selection (Table below).

In order for two species within the same area to adapt, they may develop different specializations in order to coexist. This is known as character displacement. An example of character displacement is when different birds adapt to eating different types of food. They can develop different types of bills, like Darwin’s Finches (Figure below).

An example of character displacement, showing different types of bill for eating different types of foods, in Darwin

Predation

Predation happens when a predator organism feeds on another living organism or organisms, known as prey. The predator always lowers the prey’s fitness. It does this by keeping the prey from surviving, reproducing, or both.

There are different types of predation, including:

• True predation.
• Grazing.
• Parasitism.

True predation happens when a predator kills and eats its prey. Some predators of this type, such as jaguars, kill large prey. They tear it apart and chew it before eating it (Figure below). Others, like bottlenose dolphins or snakes, may eat their prey whole. In some cases, the prey dies in the mouth or digestive system of the predator. Baleen whales, for example, eat millions of plankton at once. The prey is digested afterward. True predators may hunt actively for prey, or they may sit and wait for prey to get within striking distance.

This example of a true predator shows a lioness actively hunting warthogs in the western corridor of the Serengeti, in Africa.

In grazing, the predator eats part of the prey, but does not usually kill it. You may have seen cows grazing on grass. The grass they eat grows back, so there is no real effect on the population. In the ocean, kelp (a type of seaweed) can regrow after being eaten by fish. Starfish can regenerate lost arms when they are eaten.

Predators play an important role in an ecosystem. For example, if they did not exist, then a single species could become dominant over others. Grazers on a grassland keep grass from growing out of control. Predators can be keystone species. These are species that can have a large affect on the balance of organisms in an ecosystem. For example, if all of the wolves are removed from a population, then the population of deer may increase. If there are too many deer, then they may decrease the amount of plants or grasses in the ecosystem.

The act of predation can be broken down into four stages:

1. Predator senses the prey.
2. Predator attacks the prey.
3. Predator captures the prey.
4. Predator eats the prey.

At each stage, predators have adaptations for getting the prey. Prey also have adaptations for avoiding predators. (Table below).

Prey sometimes avoid detection by using camouflage (Figure below). Camouflage means that species have an appearance (color, shape or pattern) that helps them blend into the background. Mimicry is a related adaptation where a species uses appearance to copy another species. For example, a non-poisonous dart frog may evolve to look like a poisonous dart frog. Why do you think this is an adaptation for the non-poisonous dart frog? Mimicry can be used by both predators and prey (Figure below).

Camouflage by the dead leaf mantis makes it less visible to both its predators and prey. If alarmed, it lies motionless on the rainforest floor of Madagascar, Africa, camouflaged among the actual dead leaves. It eats other animals up to the size of small lizards.

An example of Batesian mimicry, where the Viceroy butterfly (right) mimics the unpalatable Monarch butterfly (left). Both species are avoided by predators to a greater degree than either one would be otherwise.

Symbiosis

Symbiosis describes a close and long-term interaction between different species. At least one species will benefit in a symbiotic relationship. There are three types of symbiotic relationships:

1. Mutualism: Both species benefit.
2. Commensalism: One species benefits while the other is not affected.
3. Parasitism: The parasitic species benefits, while the host species is harmed.

An example of a mutualistic relationship is between herbivores (plant-eaters) and the bacteria that live in their intestines. The bacteria get a place to live while they also help the herbivore to digest food. Both species benefit, so it is a mutualistic relationship.

The Ocellaris clownfish and the Ritteri sea anemones also have a mutualistic relationship. The clownfish protects the anemone from anemone-eating fish, and the stinging tentacles of the anemone protect the clownfish from predators (Figure below).

Commensal relationships may involve an organism using another for transportation or housing. For example, spiders build their webs on trees. The spider gets to live in the tree, but the tree is unaffected.

An example of a parasite is a hookworms. Hookworms live inside of humans and cause them pain, but the hookworms must live inside of a host in order to survive. Parasites may even kill the host they live on. Parasites are found in animals, plants, and fungi.

A mutualistic relationship between the Ocellaris clownfish and the Ritteri sea anemone. Myako Island, Japan. The fish protects the anemone from anemone-eating fish, while the anemone protects the clownfish from its predators, with its stinging tentacles. The clownfish has a special mucus which protects it from the tentacles.

Lesson Summary

• A community is a collection of populations of different species interacting with one another in the same area.
• Community interactions include competition, predation, and symbiosis.
• Intraspecific and interspecific competition occur when individuals share a limiting resource in the same area.
• The competitive exclusion principle plays an important role in natural selection.
• Types of predation include true predation, grazing, and parasitism.
• Prey use different adaptations to avoid detection, attack and capture by predators.
• Symbiosis includes mutualism, commensalism, and parasitism.

Review Questions

Recall

1. Define competition.

2. What is the difference between intraspecific and interspecific competition?

3. Name three different types of predation.

4. In the mutualistic relationship between the Ocellaris clownfish and the Ritteri sea anemones, what benefit does the fish get?

Apply Concepts

5. If two similar species do not live in the same area, would you expect the two species to compete? Why or why not?

6. How might a predator lower a prey’s fitness?

7. In most types of grazing, does the predator lower a prey’s fitness? Why or why not?

8. A drone fly looks a lot like a bee, yet it is completely harmless, as it cannot sting at all. What anti-predator mechanism is the drone fly using? Would you expect predators to always avoid drone flies?

Critical Thinking

9. Choose one of the symbiotic relationships: mutualism, parasitism, or commensalism. Think of an example of that type of symbiosis. Explain why it is that type.

Further Reading / Supplemental Links

en.wikipedia.org/wiki/Symbiosis

Points to Consider

• How do you think predation helps a species to survive?

Ecosystems

Lesson Objectives

• Define ecosystem.
• Discuss how biotic and abiotic factors play a role in ecosystems.
• Explain what a niche is and its importance in an ecosystem.
• Describe what a habitat is and how an organism is adapted to live in the habitat.

Check Your Understanding

• What is a community?
• What are the different types of community interactions?

Vocabulary

What is an Ecosystem?

The next level after community is an ecosystem. An ecosystem consists of all the biotic factors (plants, animals and micro-organisms) interacting with all of the abiotic factors (water, soil, and air, for instance) in the same area.

You can find an ecosystem in a large body of freshwater or in a small piece of dead wood. Other examples of ecosystems include the coral reef, the Greater Yellowstone ecosystem, the rainforest, the savanna, the tundra, the desert and the urban ecosystem (Figure below).

An example of a desert ecosystem in Baja California, showing Saguaro cacti.

Ecosystems need energy. They mostly get their energy in the form of sunlight. Matter is also recycled in ecosystems. Recycling of nutrients is important so they can always be available. Elements like carbon, nitrogen, and water are used over and over again by organisms. Human ecosystems could be a household, neighborhood, college, or even a nation. Human ecosystems interact with each other. Since humans live virtually all over the planet today, nearly all ecosystems could be considered human ecosystems.

In 2005, the largest assessment ever conducted of the earth’s ecosystems was done by a research team of over 1,000 scientists. The study concluded that in the past 50 years, humans have altered the earth’s ecosystems more than any other time in our history.

Biotic and Abiotic Factors

Biotic factors of an ecosystem include all living parts. Examples of biotic factors include bacteria, fungi, unicellular and multicellular plants, and unicellular and multicellular animals.

Abiotic factors are non-living chemical and physical factors in the environment. The six major abiotic factors are water, sunlight, oxygen, temperature, soil and climate (such as humidity, atmosphere, and wind). Other factors include carbon dioxide, geography, and geology.

Abiotic and biotic factors interact within ecosystems and also between ecosystems. For example, water may be recycled between ecosystems, by the means of a river or ocean current. Some species, such as salmon or freshwater eels, move between marine and freshwater ecosystems.

Niche

Each organisms plays a particular role, or niche, in its ecosystem. A niche is the role a species or population plays in the ecosystem. In other words, a niche is how an organism “makes a living.” A niche will include the food of an organism and how it obtains its food and space. Different species can hold similar niches in different locations. The same species may occupy different niches in different locations. Species of the Australian grasslands have the same niche. Once a niche is left vacant, other organisms can fill that position. When the tarpan, a small, wild horse found mainly in southern Russia, became extinct in the early 1900s, the niche was filled by a small horse breed, the konik (Figure below).

The konik horse, which filled the niche left by the tarpan, a horse that became extinct in the early 1900s in southern Russia.

When plants and animals are introduced, either intentionally or by accident, into a new environment, they can occupy new niches or the existing niches of native organisms. Sometimes new species out-compete native species. They can even become a serious pest.

For example, kudzu, a Japanese vine, was planted in the southeastern United States in the 1870s to help control soil loss. Kudzu had no natural predators, so it was able to out-compete native species of vine and take over their niches (Figure below).

Kudzu, a Japanese vine, introduced intentionally to the southeastern United States, has out-competed the native vegetation.

As discussed in the previous lesson, the competitive exclusion principle states that if niche overlap occurs, either one species will be excluded, character displacement will happen (as in Darwin’s Finches), or the species will go extinct.

Habitat

The habitat is the environmental area where a particular species lives (Figure below). Abiotic factors are used to describe a habitat. The average amount of sunlight received each day, the range of annual temperatures, and average yearly rainfall can all describe a habitat. These and other factors will affect the kind of traits an organism must have in order to survive there (Figure below and Figure below).

Santa Cruz, the largest of the northern Channel Islands, has the most diverse of habitats in the sanctuary, including a coastline with steep cliffs, coves, gigantic caves, and sandy beaches.

Another example of a type of habitat, showing a meadow and representative vegetation.

The above image shows wetland reeds, another type of habitat.

Habitat destruction means what it sounds like - a species' habitat is destroyed. Habitat destruction can cause a species' population to decrease. If bad enough, it can also cause species to go extinct. Clearing large areas of land for housing developments or businesses can cause habitat destruction. Poor fire management, pest and weed invasion, and storm damage can also destroy habitats.

National parks, nature reserves, and other protected areas all preserve habitats. The Environmental Problems chapter will discuss habitat destruction in further detail.

Habitats can also be examined from a human point of view. The environments where we live, work, and reproduce are our habitats.

Lesson Summary

• An ecosystem consists of all the biotic and abiotic factors interacting together in an area.
• Biotic factors include all living components of an ecosystem. Abiotic factors are the non-living chemical and physical factors in the environment.
• The niche concept is one of the most important ideas associated with ecosystems.
• If niche overlap occurs, then the competitive exclusion principle comes into play.
• The habitat is the area where a particular species, species population, or community lives.
• Habitat destruction is a major cause of population decrease, leading to possible extinction.
• Both the ecosystem and habitat can be looked at from a human point of view.

Review Questions

Recall

1. Give three examples of ecosystems.

2. List the six most common abiotic factors.

3. What is a niche?

4. Give an example of an organism filling a vacant niche.

5. What is a habitat?

Apply Concepts

6. Why might a newly introduced species become a pest?

7. Name three abiotic factors that can be used to describe a habitat.

8. Give one example of an organism and its niche that is not included in the chapter.

Critical Thinking

9. Species that travel distances between important areas for their survival, like migrating birds, may be particularly vulnerable to habitat destruction. How might the creation of multiple national parks or nature reserves help such species?

Further Reading / Supplemental Links

Points to Consider

• Now that you understand what makes up an ecosystem, what additional factors do you think might be added to get to the next level, the biome?
• How do you think what you have learned about abiotic and biotic factors might be applied to the classification of different biomes?
• The biosphere is considered to be a global ecological system. Given all you now know about ecology, what do you think the biosphere consists of?

Biomes and the Biosphere

Lesson Objectives

• Explain what biomes are.
• Describe terrestrial biomes.
• Describe aquatic biomes.
• Describe the features of the biosphere and list specific systems.

Check Your Understanding

• What is an ecosystem?
• How do ecosystems relate to humans?

Vocabulary

• aquatic biomes
• elevation
• GAIA hypothesis
• humidity
• latitude
• terrestrial biomes

What are Biomes?

The biome is the highest level of organization in ecology. Biomes include populations, communities, and ecosystems. A biome is an area with similar geography and climate that includes similar communities of plants and animals.

There are into two major groups of biomes:

1. Terrestrial biomes (land).
2. Aquatic biomes (water).

Different biomes are habitats for different organisms. For example, one may find algae only in the part of the ocean where there is light, while conifers may be mostly found in mountains.

The diversity of animals and plants that can live in a specific biome is determined by the abiotic factors. For example, where there is more land, there are more species. Near the equator, there is also more biodiversity, probably because there is more water caused by high humidity levels.

Biomes are classified in terms of two factors:

Using these two factors, the World Wildlife Fund (WWF) identified fourteen biomes. They then divided those 14 biomes into 825 terrestrial ecoregions.

Biomes are often given local names. For example, a "temperate grassland" biome is known as "steppe" in central Asia, "prairie" in North America, and "pampas" in South America.

Terrestrial Biomes

Different terrestrial biomes are defined in terms of their plant structures (such as trees, shrubs, and grasses), leaf types (such as broadleaf and needleleaf), and plant spacing (forest, woodland, savanna). Climate also affects what type of terrestrial biomes will exist in a specific area. The following factors affect biome type:

• Latitude means how far a biome is from the equator. Moving from the poles to the equator, you will find Arctic, boreal, temperate, subtropical, tropical biomes.
• Humidity is the amount of water in the air. Air with a high concentration of water will be called humid. Moving away from the most humid climate, biomes will be called semi-humid, semi-arid, or arid (the driest).
• Elevation measures how high land is above sea level. Higher elevations have a similar affect on biomes as increasing latitude.

Terrestrial biomes (Figure below) lying within the Arctic and Antarctic Circles do not have very much plant or animal life. Biomes with the highest amount of diversity are near the equator (Figure below).

One of the terrestrial biomes, taiga, is a coniferous evergreen forest of the subarctic, covering extensive areas of northern North America and Eurasia. This taiga is along the Denali Highway in Alaska. The Alaska Range is in the background.

Another terrestrial biome is tropical rainforest. The one pictured here is located in the Amazon basin north of Manaus, Brazil. The image was taken within 30 minutes of a rain event, and a few white clouds above the canopy are indicative of rapid evaporation from wet leaves after the rain.

Aquatic Biomes

Aquatic biomes can be defined according to:

• Size.
• Depth.
• Vegetation, such as a kelp forest.
• Animal communities.

According to the WWF scheme, freshwater biomes can be classified as the following:

• Large lakes (Figure below).
• Large river deltas.
• Polar freshwaters.
• Montane freshwaters (in mountain areas).
• Temperate coastal rivers.
• Temperate floodplain rivers and wetlands.
• Temperate upland rivers.
• Tropical and subtropical coastal rivers.
• Tropical and subtropical floodplain rivers and wetlands.
• Tropical and subtropical upland rivers.
• Xeric (dry habitat) freshwaters and endorheic (interior drainage) basins.
• Oceanic islands.

The WWF classifies marine (salt or ocean water) biomes according to:

• Polar habitat types.
• Temperate seas.
• Temperate upwelling.
• Tropical upwelling.
• Tropical coral.

Other marine habitat types include:

• Continental shelf.
• Littoral/intertidal zone.
• Coral reef.
• Kelp forest (Figure below).
• Pack ice (Figure below).
• Hydrothermal vents.
• Cold seeps.
• Benthic zone.
• Pelagic zone.
• Neritic zone.

An example of an aquatic marine biome, a kelp forest, located near Santa Cruz Island, Channel Islands National Park, California.

An example of an aquatic marine biome, pack ice.

Lake Tahoe in Northern California is a freshwater biome.

The Biosphere

The highest level of ecology is the biosphere. It is the part of the Earth, including the air, land, surface rocks, and water, where you can find life.

The biosphere interacts with the:

• Lithosphere: sphere of soils and rocks.
• Hydrosphere: water.
• Atmosphere: air.

The biosphere includes an area between 11,000 meters below sea level to 15,000 meters above sea level. It overlaps with the above three spheres.

The GAIA hypothesis states that the biosphere is its own living organism. The hypothesis explains how biotic and abiotic factors interact in the biosphere.

The atmosphere, hydrosphere and lithosphere are cooperating systems that produce a biosphere full of life.

Lynn Margulis, a microbiologist, added to the hypothesis, specifically noting the ties between the biosphere and other Earth systems. For example, when carbon dioxide levels increase in the atmosphere, plants grow more quickly. As their growth continues, they remove more carbon dioxide from the atmosphere.

For a better understanding of how the biosphere works and various dysfunctions related to human activity, scientists have simulated the biosphere in small-scale models. Biosphere 2 (Figure below) is a laboratory in Arizona that contains 3.15 acres of closed ecosystem. BIOS-3 was a closed ecosystem in Siberia, and Biosphere J is located in Japan.

Biosphere 2, in Arizona, contains 3.15 acres of closed ecosystem and is a small-scale model of the biosphere.

Direct human interactions with ecosystems, including agriculture, city development and other land uses, affect the health of the biosphere and their ecosystems. In terms of the human impact on biomes and ecosystems, the study of ecology is now more important than ever. Scientists that study ecology will move us toward an understanding of how best to live in and manage our biosphere.

Lesson Summary

• A biome is an area with similar geography and climate that contains ecologically similar communities of plants and animals.
• Biomes are classified in different ways, sometimes according to differences in the physical environment, and sometimes according to latitude and humidity.
• Biodiversity of each biome is determined by abiotic factors, such as water and temperature.
• Terrestrial biomes are classified based on various plant factors and on climate.
• Aquatic biomes are classified based on various factors and divided into freshwater and marine biomes.
• The biosphere is a global ecological system.
• The biosphere is itself a living organism, as explained by the GAIA hypothesis.
• Humans have changed global patterns of biodiversity and ecosystem processes.

Review Questions

Recall

1. Define biome.

2. What is the difference between a terrestrial and an aquatic biome?

3. Name a type of biome based on the physical environment.

4. Name the aquatic biomes classified according to depth.

5. What is the GAIA hypothesis?

Apply Concepts

6. Where would you expect to find more biodiversity, in a rainforest on the equator, or in a desert? Explain why.

7. As you climb a mountain, you will see the vegetation a habitat type change as you gain elevation. What kind of change will result in a similar change in habitat?

8. Name one way that human activity has affected the biosphere (maybe you have heard something on the news?)

Critical Thinking

9. Water is recycled between the hydrosphere, lithosphere, atmosphere, and biosphere in regular cycles. Why do you think oceans are important for this type of water recycling?

Further Reading / Supplemental Links

Points to Consider

You now have a general idea of what a biome is and how the diversity of a biome is related to other factors. The next chapter, on ecosystem dynamics, will give you a greater understanding of how energy flow, cycling of matter, and succession vary from one biome to another.

• One of the aquatic biomes, the hydrothermal vents, is not dependent on sunlight but on bacteria, which utilize the chemistry of the hot volcanic vents. Can guess where these bacteria fit into the flow of energy in such an ecosystem?