How is the structure of ecosystem like?

Three indicators were employed to describe the ecosystem or food web structure. They were trophic level, length of food chain and number of functional groups. In some ocean food webs, the theoretic trophic levels could reach eight because of their omnivorous characteristics, but the energy flux length never exceed five levels, so the concept of “effective trophic levels” was used. Any functional group has its own specific trophic level. The mean of effective trophic levels can describe the structure of whole consumer food web. With the same reason, the mean length of food chain can describe the food web structure more truly than the “maximum of food chain length”.

The mean of effective trophic level of primary producers, cultivation-husbandry food webs and ocean cost food webs increased from 1.0 to 3.3, step by step. For soil food web, the length of food web was more widely adopted than trophic level. The mean of food chain length in farmland soil was 3.5.

The value variation in the number of functional groups was much bigger than in trophic levels or food chain length. In this paper, it ranged from 1 to 36. The number of functional groups from low to high was: primary producers, cultivation-husbandry food webs, soil food webs, ocean food webs. This change trend was consistent with the trend of trophic level or food chain length. While the number of functional groups increased, the other two indicators increased synchronously.

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