Because plants produce all the sugar and oxygen used by animals, they are considered the producers of the ecosystem. All life on Earth is made possible by the presence of producers.

Animals, on the other hand, are consumers. This means that they have to eat other organisms, such as plants, to gain energy.

Together, producers and consumers form food chains and food webs.

For example, an aspen tree produces sugar in photosynthesis during the summer months. When winter arrives, the tree stores some of this sugar in its bark and roots. A mountain hare eats the leaves and bark of the aspen. By doing so, it gains some of the sugar stored in the aspen. This makes the mountain hare a herbivore. A fox, on the other hand, is a predator. It can eat the mountain hare, and receive the energy the hare has gained from the aspen.

Therefore, the energy created by the producer (aspen) is transferred first into the herbivore (mountain hare) and finally into the predator (fox). This is an example of a food chain. Together, the food chains of a ecosystem form an intricate food web.

The arrows of the food chain show how energy moves from a producer to a herbivore, and finally to a predator. 

When predators and other organisms die, decomposers arrive at the scene. These decomposers, such as fungi and insects, gain their energy from breaking down the material contained in dead organisms. At the same time, they release the nutrients contained in these organisms back into the ground, where they can be collected by plants.