© Shell Education #50162—Leveled Texts for Science: Life Science

101

EcosystemsJackrabbits are a kind of hare. They live in the Mojave Desert.

You might think that there isn’t much life in the desert. The hare knows better. Every day it finds plants to eat. The hare eats sagebrush. It eats mesquite. It even eats cactus! The hare also has to watch out. There are predators out there. Coyotes and eagles eat hares.

There is a lot of life in the hare’s world. The desert is full of living things. They need each other to live. The hare needs the plants for food. The coyotes need hares for food. Even the plants need the animals. All the living things form an ecosystem. That is the group of all the living things that need each other.

The number of living things must stay balanced. Too many hares will eat too many plants. They will eat them faster than they can grow back. Too many coyotes will run out of food as well.

Isle Royale

Scientists watched a pair of moose. The moose swam out to an island. It was called Isle Royale. Ten years later, there were three thousand moose! There weren’t enough plants to eat. The moose started to die. Then a pair of wolves showed up. They ate the moose. They had lots of baby wolves. But soon there were too many wolves. They starved. At last, 600 moose and 20 wolves lived on the island. This was just enough to keep them both from starving.

#50162—Leveled Texts for Science: Life Science © Shell Education

10�

What is a Biome?

Earth is split up into areas called biomes. Desert is a biome. Each biome has its own climate. A desert has dry weather. It has sand or rocks instead of soil. This means only some kinds of plants and animals can live there.

Biomes are defined by two things. Altitude measures how high a place is. Latitude is a part of how hot a place is. These two things make a place this biome or that biome.

Altitude measures the height above the sea. It affects what can grow. Trees will only grow so high up a mountain. They stop at the tree line. Above the line, it is too windy and cold. Most of the soil has blown away. There are only rocks. Only short plants can grow high up on a mountain. Sheep, elk, chinchillas, and birds live here and eat these plants.

Latitude is how far a place is from the equator. That is the middle of Earth. It is halfway between the North Pole and the South Pole. Close to the equator, the weather tends to be hot. Close to the poles, the weather starts to get cold.

In the far north, summers are short. It is too cool for trees. Only short grass, lichens, and mosses grow here. This is the tundra biome. These plants can live at low temperatures. They use the long days with lots of light. Caribou eat the grasses. Polar bears may eat the caribou.

Near the equator, it is near 25 °C (77 °F) year round. It rains all the time. This is the tropics. This is where you will find rainforests. Here there are many kinds of living things. The rainforests cover less than 7 percent of Earth’s land. Yet they have more than half the Earth’s species!

Comprehension QuestionWhat happened to the moose on Isle Royale?

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© Shell Education #50162—Leveled Texts for Science: Life Science

10�

EcosystemsJackrabbits live in the Mojave Desert. You might think that

there isn’t much life in the middle of the desert. The jackrabbit knows better. Every day it finds plants to eat. It eats sagebrush and mesquite. It even eats cactus! It also has to watch out. There are predators out there. Coyotes and eagles eat jackrabbits.

There is a lot of life in the jackrabbit’s world. There are lots of living things in the Mojave Desert. They depend on each other to live. The jackrabbit needs the plants for food. The coyotes need jackrabbits for food. Even the plants need the animals. All the plants and animals form an ecosystem. That is the group of all the plants and animals that need each other.

The number of plants and animals must stay balanced. Too many jackrabbits will eat too many plants. They will get eaten faster than they can grow back. Too many coyotes will run out of food as well.

Isle Royale

Scientists watched what happened when a pair of moose swam out to an island called Isle Royale. Within 10 years, there were 3,000 moose! But there weren’t enough plants to eat, so they started to die. Then a pair of wolves arrived. Eating the moose made the wolves’ numbers grow. But soon there were too many wolves, and they starved. At last, 600 moose and 20 wolves lived on the island. This was just enough to keep them both from starving.

#50162—Leveled Texts for Science: Life Science © Shell Education

10�

What is a Biome?

Earth is split up into areas called biomes. Each biome has its own climate. A desert has dry weather and sand or rocks instead of soil. This affects the kinds of plants and animals that can live there.

Biomes are defined by two things. Altitude measures how high a place is. Latitude helps determine how hot a place is. These two things make a place this biome or that biome.

Altitude measures the height above sea level. It affects what can grow. For example, trees will only grow up to the tree line on a mountain. Above the tree line, it is too windy and cold. Most of the soil has blown away, leaving only rocks. Only short plants can grow in this alpine biome. Sheep, elk, chinchillas, and birds live here and eat these short plants.

Latitude is how far a place is from the equator. The equator is at the middle of Earth. It is halfway between the North Pole and the South Pole. Close to the equator, the weather tends to be hot. Far away from the equator, the weather starts to get cold.

In the far north, summers are short. It is too cool for trees. Only short grass, lichens, and mosses grow here. This is the tundra biome. These plants can do photosynthesis at low temperatures. They use the long spells of daylight. Caribou eat the grasses and polar bears may eat the caribou.

Near the equator, it is near 25 °C (77 °F) year round. It rains all the time. This is where you will find tropical rainforests. Here there are millions of kinds of plants and animals. The rainforests cover less than 7 percent of the land on the planet. Yet they have more than half the Earth’s plant and animal species!

Comprehension QuestionWhat happened to the moose and wolves on Isle Royale?

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© Shell Education #50162—Leveled Texts for Science: Life Science

10�

EcosystemsJackrabbits live in the Mojave Desert. You might think that

there isn’t much life in the middle of the desert. The jackrabbit knows better. Every day, the jackrabbit finds plants to eat. It eats sagebrush, mesquite, and even cactus! It also has to watch out for predators. Coyotes and eagles eat jackrabbits.

There is a lot of life in the jackrabbit’s world. All the living things in the Mojave Desert depend on one another to survive. The jackrabbit needs the plants. The coyotes need jackrabbits to eat. Even the plants need the animals. Together, the plants and animals form an ecosystem. An ecosystem includes all the plants and animals that need one another.

The number of plants and animals must stay balanced. Too many jackrabbits will eat the plants faster than they can grow back. Too many coyotes will run out of food as well.

Isle Royale

Scientists observed what happened when a pair of moose swam out to an island called Isle Royale. Within 10 years, there were 3,000 moose! But there weren’t enough plants to eat, so they started to die. Then a pair of wolves arrived. Eating the moose made their numbers grow. But soon there were too many wolves, and they starved. At last, 600 moose and 20 wolves lived on the island. This was just enough to keep them both from starving.

#50162—Leveled Texts for Science: Life Science © Shell Education

10�

What is a Biome?

Earth has different areas called biomes. Each biome has its own climate. For example, a desert has dry weather and sand or rocks instead of soil. This affects the kinds of plants and animals that can live there.

Altitude and latitude determine biome boundaries. Altitude measures how high a place is. Latitude helps determine how hot a place is.

Altitude measures the height above sea level. It affects what can grow. For example, trees will only grow up to the tree line on a mountain. Above that, it is too windy and cold. Most of the soil has blown away, leaving only rocks. Only short plants can grow in this alpine biome. Sheep, elk, chinchillas, and birds live here and eat these plants.

Latitude measures the distance from the equator. The equator is an invisible line around the middle of Earth. The closer a place is to the equator, the hotter the weather. The farther away from the equator, the cooler the weather gets.

In the far north, summers are too short and cool for trees. Only short grass, lichens, and mosses grow in the tundra biome. These plants can do photosynthesis at low temperatures with long spells of daylight. Caribou eat the grasses and polar bears may eat the caribou.

Near the equator, the average temperature is near 25 °C (77 °F) year-round. It rains all the time. This is where you will find tropical rainforests. Tropical rainforests have millions of different plants and animals. They cover less than seven percent of the land on the planet. Yet they support more than half the Earth’s plant and animal species!

Comprehension QuestionHow did the Isle Royale ecosystem become balanced?

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© Shell Education #50162—Leveled Texts for Science: Life Science

10�

EcosystemsJackrabbits live in the Mojave Desert. You might think that

there isn’t much life in the middle of the desert, but the jackrabbit knows better. Every day, the jackrabbit finds plants to eat: sagebrush, mesquite, and even cactus! The jackrabbit also has to watch out for predators like coyotes and eagles.

There is a lot of life in the jackrabbit’s world. All the living things in the Mojave Desert depend on one another to survive. The jackrabbit needs the plants, the coyotes need jackrabbits to eat, and even the plants need the animals. Together, the plants and animals form an ecosystem. An ecosystem includes all the plants and animals that need one another.

The populations of plants and animals exist in a delicate balance. Too many jackrabbits will eat the plants faster than they can grow back; too many coyotes will run out of prey.

Isle Royale

Scientists observed what happened when two moose swam out to an isolated island called Isle Royale. Within 10 years, there were 3,000 moose, but there weren’t enough plants to eat, so they started to die. Then a pair of wolves arrived, and they began to hunt the moose. Eating the moose made their numbers grow, but soon there were too many wolves, and they starved. At last, 600 moose and 20 wolves lived on the island: this was just enough to keep them both from starving.

#50162—Leveled Texts for Science: Life Science © Shell Education

10�

What is a Biome?

Earth has different areas called biomes; each biome has its own climate. For example, a desert’s low precipitation results in sand or rocks instead of soil. This determines the kinds of plants and animals that can live there.

Altitude and latitude determine biome boundaries. Altitude measures how high a place is. Latitude helps determine how hot a place is.

Altitude measures height above sea level, and it has a significant impact on what can grow. For example, trees only grow up to a mountain’s tree line. Above this invisible line, it is windy and cold and most of the soil has blown away, leaving only rocks. Only short plants can grow in this alpine biome, and sheep, elk, chinchillas, and birds eat these plants.

Latitude measures the distance from the equator. The equator is an invisible line around the middle of Earth. The closer a place is to the equator, the hotter the weather. The farther away from the equator, the cooler the weather gets.

In the far north, summers are abbreviated and the average temperature is too cool for trees. Only short grass, lichens, and mosses grow in the tundra biome. These plants can perform photosynthesis at low temperatures with long spells of daylight. Caribou eat the grasses; polar bears may eat the caribou.

Near the equator, the average temperature is near 25 °C (77 °F) year-round. It rains all the time. This is where you will find tropical rainforests. Tropical rainforests have millions of different plants and animals. They cover less than 7 percent of the land on the planet. Yet they support more than half the Earth’s plant and animal species!

Comprehension QuestionDescribe how ecosystems become balanced.

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