An ecosystem is a group of organisms that live in generally close proximity and that depend upon each other for survival. When the balance between different parts of any ecosystem is affected, all parts of the ecosystem are impacted.
Plants give off oxygen as a byproduct of photosynthesis, which is needed for respiration by animals that may live in the ecosystem. In order for plants to complete the process of photosynthesis, they remove carbon dioxide from the atmosphere, which helps animals. Many types of animals eat parts or all of various types of plants for nutrition. Some animals use plants for habitat and/or for protection from enemies, as in camouflage. All of these functions are critical for the animals in the ecosystem. In turn, the animals serve important roles in allowing the plants to survive.