The process of succession results from changes in the climate, and from fires, earthquakes, wind storms, floods, and human activities. Changes are also made by the community's previous organisms, which make the habitat suitable to a new plant community. This process is called transpiration. The species position in a food chain is called the trophic level. It provides the level occupied by the species in the process of energy transfer through the ecosystem.
Plants occupy the first feeding or trophic level as they make food directly from the sun's energy.
Herbivores eat the plants and are at the second trophic level. A raccoon is at the second feeding or trophic level when consuming nuts and at the third trophic level when eating a crayfish. An ecosystem reuses water through the water cycle. Water enters the atmosphere as vapour from bodies of water and from the soil. Plants lose water through the pores in their leaves.