?In an ecosystem, the organisms composing the
populations and communities all require energy for survival. That energy can come from the sun in the case of the plants, or from food, in the case of the animals. The original source of energy in most ecosystems is the sun; the plants use the light for photosynthesis, which converts the light energy into basic sugars, which the plant uses as its food and stores in the form of sugars, starches, and other plant material. The animals derive all of their energy from the energy from plants stored in their bodies. The animals are divided into
different trophic levels depending on if they eats the plants for their energy supply, if they eat the animals that ate the plants, or if they eat the animals that ate the animals that ate the plants.
3. Trophic structures or levels of ecosystems 生态系统的能量结构
3.1 Food Chains 食物链A ecosystem looks inordinance. Actually, all components are interconnected orderly through the food relationships, thus form chain structure, called food chain or trophic chain
For example: Silkworm-Mantis-yellowbird指生物界食物关系中，甲吃乙、乙吃丙、丙吃丁的现象。生物之间这种能量转换连续依赖的次序称为食物链。
?Trophic Levels Producers-the plants storing the
energy as food. Herbivores-the animals which eat the plants. i.e., Cows, Parrotfish, Humans. Carnivores-the animals which eat the animals which ate the plants. i.e., Coyotes, Barracuda, Humans. Second Level Carnivores-the animals which ate the first level carnivores. i.e., Bears, Sharks, Humans. Third Level Carnivores-very rare Fourth Level Carnivores-some do exist Decomposers-break down the complex organic molecules of dead organisms from all trophic levels. Mostly Bacteria, also Hagfish, funguses, etc.
3.1.1 The types of food chain 食物链类型：1) Grazing Trophic Chain:The energy transfers from
Autotroph—Herbivores—Carnivores, are referred to as草牧食物链（捕食食物链）: 是以绿色植物为基础，从草食动物开始的食物链，草原和水体生态系统是以草牧食物链为主的生态系统。
2) Decomposer or Detritus Trophic Chain : Trophic chains commencing with dead organic matter and involving saprotrophs are referred to as
?腐生食物链（碎食食物链）: 指以死有机物质为基础，从腐生物开始的食物链。森林是以腐生食物链为优势的生态系统。在森林中，有90%的净生产是被腐生生物所分解消耗的。