Food producers like plants use the Sun's energy and nutrients from the abiotic environment to make food. The energy and nutrients in this food is passed on to
• heterotrophs such as animals when they feed on plants and on one another; and
• decomposers when they feed on dead organisms.
As the energy in food is passed from organism to organism, it eventually escapes into the environment and cannot be reused. The nutrients, however , are released into the abiotic environment and can be reused again by food producers.
Thus, an ecosystem is actually a functional unit in which there is
• a flow of energy , and
• a recycling of inorganic nutrients.
The sizes of biotic populations adjust according to the amount of food that is available for each population. These characteristics make the ecosystem self supporting.
