Carbon Dioxide

Plants breathe in carbon dioxide (CO2) which is produced by animals. They breathe out oxygen, which animals need to live. In the respiration cycle plants and animals are dependent on each other to exist.

Soil

Plants on land need to penetrate soil with their roots in order to stay in place and to collect water and nutrients. Some fungi and bacteria break rock and clay into soil that is usable for some plants, but most rely on an animal--the earthworm--to break up soil for them.

Nutrients

Plants need to collect nitrogen and other nutrients from the soil. These nutrients come from dead and decaying organisms and animal urine and feces. This is another cycle of dependence: animals eat plants, then provide nutrients for more plants to grow.

Pollination

Pollen is the sex cells of plants. It must move from flower to flower for seeds to grow. Some plants are self-pollinating or pollinated by the wind, but the vast majority rely on animals to carry their pollen for fertilization. Many insects and a few species of birds and bats are pollinators.

Seed Dispersal

Animals carry seeds from place to place on their bodies and in their feces. Some plants are so reliant on animals that their seeds must pass through the gut of a particular species in order to grow.

Complex Ecosystems

In some ecosystems, plants rely on a series of grazing animals to clear the way for them to grow. These plants only grow after an animal has eaten other plants in the area. Other types of plants only produce seeds after an animal has eaten their leaves. All organisms currently alive on Earth evolved together. None can be removed without eliminating many others.

Source:

Integrated Principles of Zoology; Cleveland P. Hickman Jr., et al.; 2004

Animal Diversity; Cleveland P. Hickman Jr., et al.; 2007

More Information:

U.S. Forest Service: Pollinators Fact Sheet

Backyard Nature: Earthworm Facts