Final answer:
Organisms are categorized in ecosystems by their roles: producers like plants create food, herbivores (primary consumers) eat the producers, carnivores (secondary consumers) eat the primary consumers, and decomposers break down dead material and waste.
Step-by-step explanation:
In many ecosystems, the various organisms are categorized based on their roles in the food chain. Producers, such as plants and phytoplankton, are at the base, creating food through photosynthesis. Primary consumers are herbivores like rabbits and deer that eat producers. Secondary consumers are usually carnivores; an example would be a snake that eats a mouse. Adding to this, decomposers, which include fungi and bacteria, break down dead material at the end of the food chain, recycling nutrients back into the ecosystem.
As an example of how these categories interact: phytoplankton (producer) is consumed by krill (primary consumer), which is then eaten by fish (secondary consumer), and finally, fish may be consumed by a shark (tertiary consumer). To complete this food chain, decomposers would break down waste and dead organisms at every trophic level, including the remains of the shark.