|
|
page 1
|
Introduction
When the environment changes, plants and animals must adapt in order
to survive. It takes many generations for a population of plants to
evolve in response to a change in the environment. Along with the
plants, the animals that eat those plants must change. If they
cannot adapt, the population will die.
In this activity, you will explore how adding a dam to the Virtual Ecosystem affects the plants and animals living there. Will some members of the grass and rabbit populations be able to survive this change?
Rabbit families
Remember when you learned that plant babies might not look exactly
like their parents? Animals are the same way, even humans! Your
grandfather may be tall, your father may be even taller and when you
grow up, you may be taller than both of them! Rabbit babies are the
same way. Does being a certain size help some rabbits?
Inherited traits are the features of animals that are passed down from parents to children. In the rabbit family below, the two parents are medium sized. Size is a trait that is inherited in rabbits, but sometimes there can be variation in size. Their offspring are mostly medium sized, but one is large and one is small. And this variation is important because different sized rabbits prefer to eat different grasses.
Grass population
You learned that there is variation in plants and grass is a type of
plant. In the Virtual Field, there are three types of grass that
rabbits like to eat. All of these plants grow well when there is
enough water. Only Grass C can live in less water. Grass C has an
advantage in dry environments. When some grass in a population can
survive changes in the environment, while the other grass dies, that
is called natural selection. A large population of grass that has
enough water will have lots of all three grass varieties. Over time,
if there is less water, the amounts of each type of grass in the
population will shift.
You also learned that each size of rabbit prefers to eat a different type of grass. On the next page, you will experiment to see what will happen to the rabbits if the environment dries out.
|
|
|
| Grass A | Grass B | Grass C |
First, make some predictions:
Go to the next page to test your predictions!
Experiment: Building a dam
Water is an important, nonliving part of every ecosystem on Earth.
People build dams across rivers for many reasons. For example, a dam
can be used to get power from the water. By changing the water
flow, a dam can affect the amount of water in an environment. What
do you think will happen to the population of rabbits living below
the dam if water is blocked from flowing there?
Instructions
1. Click the rabbit button to add a population of rabbits to the Virtual Ecosystem. Click the plant button to add a population of grass.
2. Press play . After a few seconds, press the button to Build Dam.
3. Watch the graphs to see how the number of rabbits changes as the water level changes below the dam. You can pause the model at any time to look at the graphs.
Your challenge: To determine how the rabbit population is
affected when a dam is built.
|
Who survived?
Think about the impact the dam had on the ecosystem. The two graphs
below show the rabbit population above and below the dam after many
years have past.
|
|
When one type of rabbit has a trait that makes it able to survive an environmental change better than others in a population, that is an advantage. The rabbits with an advantage will live and be able to have more babies. That is natural selection.
Experiment: Removing the dam
Sometimes dams do more harm than good to an environment and they are
removed. In this experiment, you will remove the dam.
Instructions
1. The Virtual Ecosystem below has a dam across the middle. Look at the two graphs to see what types of rabbits live in the top half of the field and the bottom half.
2. Press play . After a few seconds, press the button to Remove the Dam.
3. Watch the graphs to see how the number of rabbits changes as the water level changes below the dam. You can pause the model at any time to look at the graphs.
Your challenge:
To determine if your prediction is correct.
|
Shift in population
Did you predict that the population would shift back and contain all
three types of rabbits? Think about how the environment changed when
the dam was removed.
Conclusion
In this activity, certain traits are selected for in a population as
the environment dried out. When there was little water, the large
rabbits had an advantage because they could eat the tall grass that
could live with less water. Large rabbits survived and had more
babies so, over time, the population of rabbits shifted to larger
sized rabbits. The small and medium sized rabbits could not eat the
tall grass, so if any smaller rabbits were born, they died before
they were old enough to have babies.
In the Virtual Ecosystem, you learned that as the environment changes, the population can shift back and forth so that plants and animals with certain traits are more likely to survive. There are many different kinds of advantages like size or color that an animal or plant can have. In the next activity, you will explore how color can be an advantage to some rabbits in the Virtual Ecosystem.
Click the X at the top of this window to close the activity and save your work.