Energy Flow and Nutrient Cycles: Producers, Consumers, Decomposers

Producers

Producers: Organisms that make their own autotrophic organic matter from inorganic matter.

Consumers

Consumers: Heterotrophs that feed on living organic matter.

• Herbivores (primary consumers): Animals that eat plants.
• Carnivores (secondary consumers): Animals that feed on herbivores. There may also be third- and fourth-order consumers.
• Omnivores: Animals that eat both plants and other animals.

Decomposers

Decomposers: Heterotrophic organisms that feed on detritus and convert it into inorganic compounds.

Food Chains and Food Webs

Food chains: Used to show who eats whom in an ecosystem. In each chain there are different levels, called trophic levels. At the first level are the producers; the higher levels are consumers.

Food web: A set of interconnected food chains that exists within an ecosystem.

Energy Flow from Producers

Energy flow: Producers manufacture organic matter. Some energy is used in respiration to operate the organism's metabolism; part is lost as waste (for example, fallen leaves or dead branches). The remainder is stored in leaves, roots, and other tissues and can be used by animals that eat those producers.

Pyramids of Energy Production

Each rectangle in an energy pyramid represents the energy stored at that trophic level and available to the next. The largest rectangle represents the producers; rectangles become smaller at higher levels because each level must provide energy to support the level above it.

Biomass Pyramid

The boxes in a biomass pyramid are proportional to the amount of biomass at each level. This pyramid can be inverted because producers may have low biomass but grow very quickly.

Pyramid of Numbers

The rectangles represent the number of individuals at every trophic level. This pyramid can also be inverted in some ecosystems.

Carbon Cycle

Plants and algae, through photosynthesis, take CO2 from the atmosphere and transform it into organic compounds. These compounds pass through all trophic levels via feeding. Part of the carbon returns to the atmosphere as carbon dioxide through respiration. The remains of dead organisms can be buried and, over long time spans, transform into coal or oil. In many water bodies, carbon is dissolved in water; when organisms die, carbon often returns to sediments.

Nitrogen Cycle

Nitrogen: Nitrogen is abundant in the atmosphere, but not all organisms can use atmospheric N2 directly. Certain bacteria convert atmospheric nitrogen into compounds that plants can use. Plants assimilate nitrogen into organic compounds. These organic nitrogen compounds are transferred to consumers through feeding. When organisms die, decomposing bacteria transform the debris back into inorganic forms so producers can take up nitrogen again.