Biological communities interact with the climate, soil, atmosphere, and water to create an ecosystem. We consider ecosystems at the end of the ecology module because ecosystems bring together every element of ecology we’ve learned so far: physical environment, individual behaviour, population ecology, and community ecology.
Each population in an ecosystem can be labeled by how it fits into the trophic interactions, or feeding interactions, between species. Species that capture sunlight energy (or energy from inorganic molecules) and build it into chemical bonds through photosynthesis (or chemosynthesis) are called primary producers. Primary producers form organic matter from inorganic matter using the energy gained from outside sources. All other organisms are consumers that gain energy from the organic matter they consume. Primary consumers eat primary producers, while secondary consumerseat primary consumers, and so on up the scale of tropic levels. Detritivores are species that consume dead organic matter. Some species, such as humans, are omnivores because they can feed on producers and consumers at more than one trophic level. The top level in a chain or web of feeding interactions is often called the top carnivore.
Trophic feeding interactions can be mapped out into a food web that groups species by trophic level and connects “enemy” (herbivore or predator) to “victim” (producer or prey) with arrows that point in the direction of energy flow.