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No species can survive by itself. Each one depends on the actions of others for its survival. Think about yourself at this very minute. What do you need RIGHT NOW at this very minute to continue living? Is it food? Possibly. Is it water? Maybe. Take a deep breath. What if there was no oxygen in the air you just inhaled? You wouldn't last very long without oxygen. Every bit of oxygen you take in is produced by a plant. Therefore, you are dependent on plants for your very survival — and you eat them, too! In this lesson, you will learn that species are dependent on others and their environment for survival.

Now you know that humans are dependent on others and the environment for survival. So, what about animals in the wild? There is a relationship between predators and prey. While the predators live off the prey, they also help the prey. Think of it this way: If there were no coyotes eating mice, there would be so many mice that they would get sick or weaken from lack of food or a disease might be spread more easily than normal. The coyotes, although they are killing individual mice for their food, are actually helping the mouse population. Think of who the coyotes catch. They catch the old, the weak, and the sick mice first. This allows the healthiest mice to survive and reproduce, which keeps the species strong as a group.

@creativecommons

Another way to think about dependence is to think of a food chain. A food chain is simply a list of what eats what until you reach the top of the chain. For example:

grass ⇒ grasshopper ⇒ frog ⇒ snake ⇒ hawk

In this example, the grasshopper eats the grass, the frog eats the grasshopper, the snake eats the frog, and the hawk eats the snake. Therefore, the hawk would be at the top of this food chain. Each species are dependent on the others for its survival.

@creativecommons

grass

@creativecommons

frog eats grasshopper

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snake eating frog

@creativecommons

hawk eating snake

In this case, the bottom of the chain is a simple seed (the grass) and the top of the chain is a hawk. If any part of this chain were not present, the entire chain would be affected. For example, if there were no grasshoppers, the number of frogs, snakes, and hawks would go down. On the other hand, if there were a large number of grasshoppers, the number of frogs, snakes, and hawks would go up because there would be more food for them!

Species are also dependent on the environment for their survival. Have you ever seen a spring where you did not see many baby deer (fawns)? This may have been caused by a harsh winter. If a winter is really bad and food is scarce for the deer, they may only have a single fawn instead of twins. This cuts down on the number of deer that will be available to reproduce when they reach maturity, which hurts the species as a whole! Species can also be affected by drought, fire, severe winds, or floods. The environment is important, and all species depend on it for their survival.

Digging Deeper!

Click here to go to the Study Jams! website to watch a video on food chains. When you have finished watching the video, click on the "close" button in the upper-right hand corner to exit the video. Then, click on the "Test Yourself" button to see how much you know about food chains.