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12.1: Defining Biological Diversity

Difficulty Level: At Grade Created by: CK-12
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What is biological diversity?

What is an endangered species? What can you do to keep a species from disappearing or becoming extinct (ek-STINKT)? These are questions that conservation biologists try to answer. Conservation biology is a field of study in which scientists try to find ways to maintain biological diversity.

“What is life? It is the flash of a firefly in the night. It is the breath of a buffalo in the wintertime. It is the little shadow which runs across the grass and loses itself in the Sunset.”


quoted in The Earth Speaks

Biological Diversity

What is biological diversity? The word diversity means variety. Diversity refers to how things are different. If you have a box full of purple crayons, the colors in me box are not diverse. On the other hand, if each crayon is a different color, your box of crayons is very diverse. The word biological refers to life or living processes. So biological diversity means the variety of life mat exists in an area.

Conservation biologists tend to look at three levels of biological diversity-habitat diversity, species diversity, and genetic diversity.

Remember that habitats are the places that contain all me resources an organism needs to live. A bullfrog's habitat may be a pond.

A species is a group of organisms that are so much alike that they can reproduce and make others like themselves. Bullfrogs, sugar maples, and dogs are three different species.

Genes are contained in almost every living cell. Genes carry genetic information from one generation to the next. Genes are responsible for most of the different characteristics of individuals and of a species. Different versions of genes may make a dog's hair brown or black, your hair curly or straight, or the leaves on a tree in your yard greener or more yellow.

Figure 11.1 How many habitats can you find around your school?

Count Your Habitats How many habitats can you find at school? Count all the habitats you can find in your school. Then write them down on a piece of paper or in your journal. Describe what makes each habitat different.

Now let's investigate the different levels of biodiversity you might see around your school. First, think about the habitat diversity around the building. Is there an open-space habitat, such as a sport field, for grass, dandelions, and ants? Are there any woods or parks near the school that provide a habitat for some birds, squirrels, and raccoons? You might even discover that the drain in the boiler room provides a perfect habitat for silverfish. But you'll see silverfish only if you look very fast when you turn on the light. The field, woods, and drain are very different from one another. But each offers a habitat for different species.

Local Species Use the same list you started that includes the different habitats around your school. List the species of living organisms you can think of or observe in each habitat. When you finish your list, look over it again. Are there any species that live in more than one of the habitats?

Now think about the species diversity you might find in various habitats around your school. You probably have many different species in each of these habitats. Some of these species may include grass, dandelions, trees, ants, birds, raccoons, animals kept in the classrooms, silverfish, spiders, and cockroaches. Can you think of any other species? Don't forget about the species sitting next to you.

Now let's investigate the genetic diversity in a species around your school. It's probably easier to focus on one species and think about how the individuals in that species differ. So let's pick you, your classmates, and your teacher! What makes you different from the people around you? What makes them different from everybody else? Do some people have black hair? Do others have blond hair? Does anyone have brown or red hair? Hair color is one example of genetic diversity in humans. What are some other types of genetic diversity you can think of? After you identify some characteristics that make humans different, think of some characteristics that make humans similar. What characteristics do humans have in common?

Now let's investigate a larger area than that around your school. Let's take an imaginary trip to the Congo River region of west and central Africa to investigate the levels of biodiversity. Flying over the region, you can see many different types of habitats. The habitat diversity of the Congo River region includes swamps, grassland, the tropical dry forest, the tropical rain forest, human villages, and the Congo River (also called the Zaire River).

Did You Know?

Rain forests aren't the only habitats so biologically diverse that they contain thousands and even millions of species. Coral reefs team with hundreds, even thousands of species. And wetlands such as marshes and estuaries support an incredible variety of birds, insects, and other organisms.

When we land and get a closer look at the living organisms, we can observe a lot of species diversity in each habitat. Our trip takes us into the tropical rain forest near the Congo River. The tropical rain forest is a large habitat, which contains millions of different species. A few of these are wild pigs, driver ants, African elephants, Myrianthusarboreus (an edible fruit tree), duikers (deer-like animals), lemurs, and gorillas.

Did You Know?

Rain forests make up only two percent of the Earth's surface. But more than half the world's wild plant and animal species live there.

As we make our way through the Congo River rain forests, we notice a band of gorillas. The gorillas would be a good species in which to investigate genetic diversity. Every once in a while a gorilla is born with a gene that does not produce melanin (MEL-uh-nin), which is the pigment that gives color to hair, skin, and eyes. These gorillas are called albinos. Albino gorillas have white fur and pink eyes. Most gorillas are dark in color. So these few albinos represent one unusual example of genetic diversity occurring among gorillas.

Figure 11.2 This figure shows examples of biological diversity in the Congo River region. Notice how biological diversity exists at many different levels.

Activity 11-1: Expedition to the Kalimantan Rain Forest


Your environment contains many different kinds of organisms. However, rain forests contain a wider variety of organisms than almost any other environment. In this activity you plan an expedition to study the biological diversity of the Kalimantan rain forest on the island of Borneo in Indonesia. Imagine that you have been invited by the government to measure the species diversity of the forest. You must count the number of different kinds of organisms you observe there. You have been given enough money to pay for supplies and three assistants to help you during one month of field study.


  • Marking pens, colored pencils, crayons
  • Paper
  • Maps, drawings, photographs of the rain forests of
  • Indonesia
  • Resource 1
  • Resource 2
  • Activity Report


Step 1 You must prepare yourself and your team for your imaginary expedition into the rain forest. You will be working and living in harsh environmental conditions. Use the following questions as a guide to find out more about the rain forest's location, climate, and surroundings as described on Resources 1 and 2:

  • What is the weather like? How hot or cold is it? How much rain falls there? What animals (especially insects) and plants will you be observing?
  • What equipment and clothing will you need to live in these conditions?
  • What scientific equipment will you need to study and record your observations in the rain forest?

Step 2 Use the information you researched to write out a packing list for what you will bring on your trip. Don't forget. The forest is so dense that you and your team will have to carry everything you need in your backpacks!

Step 3 Draw a picture of you and your team prepared to walk into the forest to begin your expedition.

Step 4 Now you are ready to explore the Kalimantan rain forest. Listen carefully while the reader describes your journey through the Kalimantan. Picture in your mind the plants and animals described in the story. Use all your senses to gather information about the forest-the sights, sounds, smells, and sensations. Then when the story is finished, discuss the questions on your Activity Report and write your answers.

Conservation biologists strive to preserve biological diversity at all levels-from genes to species to habitats. One challenge in achieving this goal is measuring biological diversity. Conservation biologists need to measure diversity so that they can track it and monitor whether or not they are achieving their goal.

One of the most common ways of measuring biodiversity is to count the numbers of species in an area. This task may seem easy to you. But it can be very challenging. For example, ecologists who want to count the species living in a specific section of the tropical rain forest have to be able to observe all of the living things in the treetops called the canopy. They also have to measure everything they observe on the ground.

Figure 11.3 Researchers have to use scaffolding and climbing gear to reach the top of the tree canopy to count the species in a rain forest.

So the ecologists counting species have to count every living organism from the ground to the canopies towering above. Making these observations can be a challenge because the treetops may be 30 meters up in the air! The ecologists often have to use ropes, climbing gear, and scaffolds just to reach the tree canopy.

Once in the canopy, the ecologists may see many insects, birds, and even plants. But they will probably miss a lot, too. Many animals are afraid of humans. Some animals are active only at night. And some animals pass through an area for only a few minutes in a day. So researchers often look for signs of animals, such as burrows, nests, chewed up food, and scat (animal droppings). As you can see, trying to count all of the species in an area can be a lot of hard work.

One of the reasons it's important to measure biodiversity is that humans tend to destroy plants and animals when they alter habitats for their own use. Although there are some habitats that haven't been significantly altered by human activities, most habitats are disturbed in one way or another. Some disturbances caused by humans are major disturbances, such as building roads, cutting down trees, and damming rivers. But humans alter habitats in more subtle ways, too, such as when they replace a meadow with a lawn.

Did You Know?

Forests provide essential services to humans. It is estimated that one mature tree consumes almost 6 kilograms (about 13 pounds) of carbon dioxide per year.

Why does biodiversity matter? Who cares if species become extinct? Don't things become extinct naturally? A species is extinct when no members of that species exist. The dinosaurs are extinct. Passenger pigeons are extinct. American chestnut trees are an endangered species, which means they may soon become extinct. In fact, many species do become extinct eventually. But usually it takes millions of years. Currently humans are causing an extinction crisis. We are altering many of Earth's habitats more and more drastically. Now species are becoming extinct at a rate much faster than at any other time, as shown in the fossil record.

The huge biological diversity of rain forests, coral reefs, and wetlands has been attracting many tourists to areas with these habitats. These tourists learn and appreciate the biodiversity, but also consume local resources and create waste. How should the local communities deal with this new development? What policies would best promote a balance between these two concerns?

As long as we have enough food, why should we care if biodiversity is decreasing and species are becoming extinct?

First of all, you know that species constantly interact with other species. All of these species' interactions affect one another and create healthy, functioning communities. If these communities fall apart, many of these services that the species provide will fall apart, too.

Here's one big example of a service provided by intact communities: What do you think would happen if all the decomposers in the world became extinct? Soon we would be up to our necks in dead animals and plants that would not decay. The cycling of nutrients would stop. Eventually, no new organisms would be able to grow, because they couldn't get the nutrients that were locked up in all of the dead bodies.

But that example is pretty dramatic. Let's look at a less drastic example of what might happen if one species, such as honeybees, became extinct. Honeybees, like other organisms in a community, provide valuable services. The pollination of plants occurs when pollen is carried from one flower to another so that the flower can be fertilized and make fruit and seeds to produce new plants. Often honeybees carry the pollen. What do you think would happen if honeybees became extinct? One obvious change is that there would be no more honey. A more important result would be that no apple tree blossoms would be pollinated, so no apples would grow. The same thing would be true for all bee-pollinated fruit crops. You would not be the only living organism to suffer. Other animals, which rely on the fruit, would be affected, too.

Figure 11.4 Disturbance of a habitat by humans can occur at different levels. Here is a meadow that becomes more and more disturbed by development.

Take a moment to consider how disturbance affects species diversity. Which do you think would have more species in Figure 11.4, the undisturbed meadow or the street with buildings? Explain the reasons for your answer.

Did You Know?

One-quarter of all medicines comes from tropical rain forest plants.

A second reason to preserve biological diversity is the present and future economic value of biodiversity. All of our domestic plants and animals came from wild species. Researchers often study the wild forms of these organisms to see if they can breed better versions for farmers. One study of better breeding is the production of drought-tolerant wheat or pestresistant potatoes. We don't know which wild species may be useful for humans in the future. So we don't want to lose any today.

Figure 11.5 Honeybees do most of the pollination of apple blossoms. If apple blossoms are not pollinated, then apples will not grow.

Wild species are an important source of medicine. About a third of all modern medicines come from different types of plants and molds. No one knows when a new medicine might be discovered. Drug companies continually test many wild plants to see if they have medicinal value. In fact, two drugs that have revolutionized the treatment of leukemia came from a little-known plant called the Madagascar periwinkle, which is shown in Figure 11.6.

Figure 11.6 The Madagascar periwinkle is a plant that is the source of two drugs used in treating leukemia.

Figure 11.7 The California gnatcatcher and the blue whale are just two of the thousands of species that are close to extinction.

A third reason to preserve all species is aesthetics (as-THET-iks). Aesthetics is beauty. The aesthetics of nature refers to the fact that the sights and sounds of nature are beautiful and pleasing to have around. For example, it's nice to have different species of plants and animals outside. Many people enjoy walking in the woods, strolling along the beach, or climbing a mountain to interact with nature's diversity. More than 30 million people in the United States say they are bird watchers. About one family out of every three feeds birds for fun. And together they spend over half of a billion dollars a year doing it! If bird diversity wasn't naturally interesting, millions of people wouldn't have so much interest in bird watching.

What Do You Think?

Do you think that it is important for humans to keep other species from becoming extinct? Review the four reasons listed. What are some other reasons you can think of for humans to preserve biodiversity?

A fourth reason to preserve biodiversity is ethics. Many people believe that all species have a right to exist whether they serve a need for humans or not. Is it our right to destroy all of the habitats of the tiny California gnatcatcher? Is it our right to hunt all of the blue whales, which are Earth's largest animals, out of existence?

Review Questions

  1. What is biological diversity?
  2. What are three levels of biodiversity?
  3. Who are conservation biologists and what do they do?
  4. How do humans affect biodiversity?
  5. What are three reasons to preserve biodiversity?

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Date Created:
Feb 23, 2012
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