Both producers and decomposers are necessary, but consumers are not.

Producers, consumers and decomposers form an interdependent whole. Producers and decomposers are indispensable biological components, and all kinds of organisms can develop stably for a long time only if they remain relatively stable.

Producers mainly refer to green plants that absorb and utilize solar energy and synthesize organic matter through photosynthesis. Solar energy fixed by producers and synthetic organic matter are the basis of energy flow and material circulation in ecosystem. This class is also called autotrophs.

Consumers refer to heterotrophs, relying on producers (green plants) to survive. According to different nutritional methods, it can be divided into two categories: primary consumers-herbivores who feed directly on plants; Secondary consumers-carnivores who feed on herbivores. There can also be three levels of consumers and so on. The latter all feed on the former. By analogy, food energy from plants is transmitted and transferred through a series of organisms. The relationship between living things and the food they eat forms a chain, which is called "food chain". For example, in grassland ecosystem, insects eat grass, frogs eat insects, snakes eat frogs, eagles eat snakes ... every link in the food chain is called "trophic level".

Decomposers also belong to heterotrophs, also known as small consumers. Such as microorganisms (bacteria, fungi, etc. ) in the biosphere, they can decompose complex animal and plant carcasses and release simple compounds that producers can reuse, which is just the opposite of producers. Decomposers are also indispensable in the cycle mechanism of ecosystems. Without decomposers, the earth will be submerged by the remains of animals and plants, and nutrients will be bound in them and cannot be recycled. Therefore, decomposers also play a very important role in the material cycle of ecosystems.