Ecosystem is mainly composed of abiotic environment, producers, consumers and decomposers.

1. Abiotic environment

Including climatic factors, such as light, temperature, humidity, wind, rain, snow and so on. Inorganic substances, such as carbon, hydrogen, oxygen, nitrogen, carbon dioxide and various inorganic salts; Organic substances such as protein, carbohydrates, lipids and humus.

2. Producer

Mainly refers to green plants, including cyanobacteria and some photosynthetic bacteria. They are autotrophs that can make food from simple inorganic substances. They can convert solar energy into chemical energy and inorganic matter into organic matter through photosynthesis, which can not only supply their own development and growth, but also provide materials and energy for other organisms, occupying the most important position in the ecosystem. The producers in freshwater ecosystem are mainly phytoplankton-algae, and some rooted plants or floating plants growing in shallow water (plants in freshwater ecosystem are divided into floating plants, emergent plants and diving plants). The producers of forest and grassland ecosystems are green plants such as herbs, shrubs and trees. In the deep sea and other similar ecosystems, producers can use the chemical energy of reducing inorganic substances such as hydrogen sulfide to synthesize bacteria (sulfur bacteria). From the point of view of nutritional dynamics, producers refer to inorganic vegetative organisms (autotrophs) or biota. T. Thienemann (1918) used this word for the first time, also known as primaryproducer, which is the basis of nutritional grade. In the common ecosystem, green plants (including microorganisms) with photosynthetic capacity account for the vast majority. Because it is responsible for the production of most organic matter, most of them only refer to green plants as producers. However, in a special ecosystem, there are many organisms that carry out chemical synthesis, and there are also many organisms with this function in lakes. In addition, taking energy as the center, chemically synthesized organisms are not regarded as producers, but belong to transformers. In a closed and stable ecosystem, the production speed (output) of producers is higher than that of consumers or decomposers. The word producer was first coined by C.G.J Peterson &; Amp Boijsen Jenison (19 1 1). At that time, the usage was different from the above, but plants or herbivores were regarded as primary consumers. But this usage is almost no longer used in the future.

3. customers

Heterotrophs mainly refers to all kinds of animals that feed on other creatures, including herbivores, carnivores, omnivores and parasitic animals.

4. Decomposer

Heterotrophs is mainly composed of bacteria and fungi, including some protozoa and large saprophytes, such as earthworms, termites and vultures. They decompose animal and plant residues, feces and various complex organic compounds, absorb some decomposition products, and finally decompose organic matter into simple inorganic matter, which can be reused by autotrophs after participating in the material cycle. The decomposer is heterotrophs, whose function is to decompose complex organic matter fixed in animal and plant residues into simple compounds that producers can reuse and release energy, and its function is opposite to that of producers. The role of decomposers in ecosystems is very important. If there is no decomposer, animal and plant residues will be piled up, substances will be locked in organic matter and will no longer participate in the cycle, and the material cycle function of the ecosystem will be terminated and the ecosystem will collapse. The role of decomposer can't be accomplished by one organism, and different organisms are needed at different stages. Decomposers are generally divided into two categories: one is bacteria and fungi (microorganisms); The other is other saprophytes (such as dung beetles, vultures, earthworms, etc. ).

Herbivores and carnivores also belong to consumers. They can't directly use solar energy to produce food, but can only get energy by directly or indirectly eating green plants. According to the different feeding status, it can be divided into a class of consumers who directly rely on plant branches, leaves, fruits, seeds and litter, such as grasshoppers, rabbits, deer, cattle, horses, sheep and other herbivores; Carnivores that feed on herbivores are secondary consumers, such as weasels, foxes and frogs. There is a law of the jungle relationship among carnivores, and the strong among them become third-and fourth-class consumers. These advanced consumers are the fiercest carnivores in the biological world, such as lions, tigers, eagles and sharks in the water. Some animals eat both plants and animals, which are called omnivores, such as some birds and fish. Consumers are in the middle of the process of material and energy transformation in the ecosystem.

The structure of ecosystem can be understood from two aspects. One is morphological structure, such as biological species, population number, spatial pattern of population, temporal change of population, vertical structure and horizontal structure of community. The morphological structure is consistent with the structural characteristics of plant community, which increases the abiotic components in soil and atmosphere, as well as the morphological structure of consumers and decomposers. The second is the nutritional structure, which is a functional unit with nutrition as the link, closely combining living things with abiotic things, forming three functional groups centered on producers, consumers and decomposers, and there is a close material circulation and energy flow between them and the environment.