What are the things you, or any organisms, need to survive?
What do you need to stay alive every day? Do you have to hear your favorite music or watch a certain show on TV? Do you need a hair dryer? Will you die if you don't have a can of soda or a bag of chips? The answer to all of these questions is, “Probably not!” But you do need some basic things to keep you going. This section will introduce some of the important resources living organisms need to survive, grow, and reproduce.
“People. . . [who]. . . live in a skyscrapered city . . . will likely forget who and where they are. If people are stopped on the street of a major city today and asked what supports the life of the earth, they will probably reply that their city does.”
Steve Van Matre
The Earth Speaks
First, you need water in some form or another. You may not often drink a glass of fresh, plain water to quench your thirst. So you may think you don't drink much water. But you probably drink plenty of water that is in juice, milk, or soft drinks. You also get some water you need from foods you eat. Without water you would dry up and die!
Food is another important requirement you need to stay alive. Remember that you need food to generate the energy to run around, grow, eat, think, talk, and do all of the other things you do. Occasionally you may miss a meal. But on the whole, you need food to stay healthy.
The last big requirement for you to stay alive is space. You probably live in some sort of structure such as an apartment building, a house, or some other dwelling. Where you live provides you the space you need to live. But the space you need to live is not restricted to your home. The space you regularly occupy probably includes your school, stores, play areas, and many more places you visit. Finally, the areas you travel through to get to all of these places are part of the space you use, too.
Figure 7.1 Common loons summer on lakes across Canada and the northern United States.
You are not the only living organism which needs water, food, and space. Water, food, and space are three of the resources you and all other organisms need to survive. A resource is something needed by an organism to live, grow, and reproduce. What are some other resources you can think of?
Resource needs can differ from person to person. For example, people who exercise a lot need more food and oxygen than people who do not exercise. Different kinds of living organisms have different resource needs, too. Compare what you need to stay alive to what an average hummingbird needs. You probably would not do very well hovering over a morning glory trying to drink its nectar. You would also have a lot of trouble building and living in a nest high in a tree.
A loon's Resources
Let's explore the world of just one species-the common loon-to find out more about resources. A species is a group of organisms that look alike and can reproduce with one another. The common loon is a species of bird. It is a black and white bird that spends its summers on lakes across the northern United States and Canada. If you saw one, you might think it was a duck, because it spends most of its time on the water paddling around, hunting, and raising its chicks. On the other hand, if you heard its call, you would never mistake it for a duck. The loon has an eerie, haunting voice that moviemakers sometimes use as background sounds for horror movies!
Loons are water birds. They have webbed feet for swimming and they are excellent divers. They have long and pointed bills for catching fish. Their dense feathers keep them warm and dry even though they spend most of their time in or on water. Swimming comes naturally to loons. Little loon chicks can swim within hours of hatching. As a matter of fact, loons are so attached to water that they leave it only when they are flying, mating, or trying to hatch eggs on their nests in the spring. In the winter, loons fly to the coasts of North America to feed, rest, and wait for the lakes on which they spend the summer to thaw.
Figure 7.2 Loons need a running start (or in their case, a paddling start) to become airborne.
After reading about the loons' attraction to water, what resource do you think a loon might need to survive? First, they need water, of course-and lots of it! Loons rarely venture onto land. They have to have a large expanse of water to use as a “runway” when trying to take off. Unlike ducks, which are light enough to take off from a standstill, loons need a chance to build up their speed before they can become airborne. If they land on a pond that is too small, they may become trapped and be unable to take off.
What do you think is another resource loons need? If you think food, you're correct. Loons need fish for food. A loon goes fishing everyday as it swims on the surface of its lake watching for fish to swim beneath it. To catch the fish, a loon first spots it swimming below. Then the loon swims swiftly underwater to grab the fish in its beak. Loons need lots of fish. One researcher calculated that a pair of loons and their two chicks could eat 430 kilograms of fish in a summer. A loon weighs only about four kilograms, which means the adults eat approximately 50 times their weight each summer. Just imagine- if you weighed 50 kilograms (about 110 pounds), you would need to eat about 2,500 kilograms (5,500 pounds) of fish in one summer to keep up with a loon!
In order for the loons to be able to spot their fish dinners, the water in the lake has to be clear, because loons chase fish underwater. The loons won't be able to see well enough to fish successfully if a lake is too cloudy. Besides being fresh, clear water, the lakes must also support lots of producers to feed the herbivores, which feed the fish the loons eat. Unfortunately, many of the producers that live in the lakes where loons live are algae. And algae tend to make lake water cloudy. So like many other organisms, loons must balance their needs. Loons balance their need between clear waters and waters rich with food.
Figure 7.3 Loons are good swimmers and can catch fish by chasing them underwater.
Think about the resources you use in a typical day. If you had to give up three resources, what would you give up? How difficult would it be to do this? Compare your resource use to a loon's. How difficult would it be for a loon to give up three of its resources?
Loons need space to survive just like we do. Loons need a large amount of space on a lake just to take off. They also need a lake big enough to support the large amount of fish they need to eat. Loons also prefer lakes with one or more small islands. Small islands are less likely than large islands, or the mainland, to have predators such as skunks, which might attack nesting loons or their eggs. Because of these space requirements, loons usually spend the summer on lakes that have more than 40 hectares of surface area. That's a lake about the size of 80 football fields.
Now review what you've just learned about the resources loons need. How would you describe the resources a loon needs each summer? A Short description of the resources might simply be water, food, and space. A more specific description would be clear lakes in the northern United States or Canada with enough surface area for taking off, and with lots of fish and small islands.
How do the three main categories of resources differ for plants and animals?
Obviously, too little of something is not good. But sometimes too much of a resource isn't good for living organisms either. In most cases, organisms need a certain amount of a resource to survive successfully-not too much or too little. For example, to grow lettuce in your garden you have to provide it with all of the resources it needs in the proper amounts. You need to provide adequate sunlight, water, and nutrients. If you try to grow lettuce in a dark closet, it simply won't grow. However, if you plant it in an extra-hot place in your garden where it gets full sun all day long, it won't grow there either. If the lettuce in your garden doesn't get enough water from rain, you have to provide additional water. But if you flood your garden, you will kill the lettuce.
Figure 7.4 A freshwater pond habitat contains all of the resources in the correct amounts for many different organisms to survive, grow, and reproduce.
You also have to provide your lettuce with the appropriate space it needs to grow. And the space has to provide the right conditions for the lettuce. You wouldn't think of sowing lettuce seeds in the middle of a driveway. You also have to provide the lettuce with enough room to grow. You won't get a healthy lettuce plant growing on one square centimeter of dirt. However, it doesn't seem likely that you could provide a lettuce plant with too much space. Sometimes resources such as space have only a lower limit or an upper limit, but not both. For example, lettuce needs a minimum amount of space, but no maximum amount.
What Do You Think?
How do you think the resources you use differ from those used by a teenager living in Bangladesh or Budapest? Which is a better use of the resources?
So you've learned what loons and lettuce plants need to live and grow. The garden or farm field where the lettuce grows is its habitat. The clear lakes in the northern United States or Canada where the loon lives is the loon's habitat. A habitat is the physical place where a plant or animal usually lives. A habitat contains all the resources required by an organism to live. But a habitat usually contains more than what is required by only one type of plant or animal. For example, freshwater lakes provide a habitat not only for loons, but also for many fish, algae, other water birds, aquatic plants, and probably a frog or two or three-or hundreds. The habitat of a lettuce plant is usually a garden that is also a habitat for other types of garden plants, slugs, beetles, and weeds. The habitat of a dog, cat, flies, ladybugs, and spiders might be where you live, too!
Activity 7-1: Too Many Bobcats
How many squirrels can live in Central Park in New York City? At first you might think that Central Park could support millions of squirrels. But when you take a closer look, you find something very different. Central Park cannot support millions of squirrels because resources are limited. Food, water, and space are called limiting resources. Food, water, and space determine the number of squirrels that can survive in an area. The ability of a habitat to supply these resources for a species is called its carrying capacity. In this activity you pretend to be bobcats while investigating the carrying capacity of a habitat. What happens when there are more bobcats than the habitat can support?
- Pieces of colored paper (6 different colors that are cut into rectangles)
- 1 Sandwich-size plastic bag
- Masking tape
- Large open area
- Activity Report
Step 1 You and your classmates are bobcats in this game of survival. But remember, survival is not a game for organisms such as the bobcat. So here are some rules you have to follow in this activity. (Remember that these rules are for this activity only. Real bobcats don't actually behave this way in nature.)
- Bobcats do not fight because it takes energy away from the food-gathering activities.
- Bobcats do not eat more than they need of one kind of food or drink more water than they need.
- Bobcats do not snatch food away from other bobcats.
- Bobcats do not take food from the den if it belongs to another bobcat.
Step 2 Gather all of the bobcats in your group in the den of your habitat area. Collect your plastic bag. Write your name on a piece of masking tape. Put your name on your bag, using the masking tape. The plastic bag will be used for collecting your food and water. Water and food items are represented in this game by rectangles of colored paper. Your collecting bag must remain in the den at all times.
Step 3 In round one, only five bobcats line up. Then, at the signal from your teacher, the bobcats go out into their habitat to get food and water. You need to collect one of each of the foods available (one rectangle of each color), as well as one sample of water (blue rectangle).
Altogether, you need to collect 6 rectangles in your plastic bag in order to survive as a bobcat. You can collect only one rectangle at a time. After you collect each one, you must bring it back to the den. You must put the rectangle in your plastic bag before you go out to collect the next one.
Step 4 When all five bobcats in your den have collected the required food and water rectangles, you may rest. Your teacher will collect and redistribute the rectangles for the next round.
Step 5 At the signal for round two, ten bobcats (the bobcats who haven't had a turn yet) will go out to collect their required food and water according to the same rules. After all the food and water have been collected, the bobcats can return to the den to rest. Your teacher will collect and redistribute the rectangles for the next round.
Step 6 At the signal for round three, all 15 bobcats will go out to collect food and water according to the same rules. When all available food and water has been collected, all bobcats return to the den.
Step 7 Find out which bobcats have survived. Remember that each bobcat needs six rectangles to survive-one of each color that represents water and five types of food.
Step 8 Analyze the game by discussing and answering the following questions. Summarize your group's discussion by writing your answers on your Activity Report.
- What happened to the bobcats in your den during each of the three rounds?
- What factors determined whether bobcats survived or not?
- What other factors might affect the carrying capacity of a habitat for bobcats? How could you alter the game to include these other factors?
- Analyze the graph on the Resource. Explain what is happening to the growth in section 2 of the graph. Why isn't the line a straight line?
- Compare the graph to what happened in the bobcat activity.
- What do you think is happening in section 4 of the graph? Why?
- Do you think the bobcats follow the rules you followed in this game of survival?
- Do you think that the Earth has a carrying capacity for humans? Explain your answer.
Define the Niche of an Animal Describe the niche of an animal of your choice. What are the resources it needs to survive? In what amounts does it need each of these resources?
If a habitat is where an organism lives, then what is a niche? Ecologists use the term niche in a very specific way. When they investigate an organism's niche, ecologists find out what resources are needed in order for it to survive, grow, and reproduce in its habitat. They look at the limits of these resources and how the organism fits in with the rest of the community. Finally, ecologists combine all of this information to describe the organism's niche-where it lives, what it needs to survive, and how it interacts with other organisms.
What is your niche in life? How do you fit in? What are the resources you need to survive? What do you like to do? What do you have to do? How do you interact with the other organisms around you in your environment?
- What is a resource? Describe three general categories of resources.
- Do all organisms require the exact same resources? Give an example or two to support your answer.
- Is it possible to have too much of a needed resource? Support your answer with an example.
- What is the difference between the habitat and the niche of a plant?