An organism's environment is everything affecting it during its lifetime. It includes both biotic (living) and abiotic (non-living) elements.
A niche is the functional role of an organism in its environment. The role of humans is one of consumer, specifically omnivore. Humans modify their surroundings, harness energy, produce waste, and control their population.
Natural selection is the process whereby successful organisms pass on the characteristics which made them successful to their offspring. In this way, each organism is finely tuned to a particular habitat and niche, and unfit individuals are removed from the population.
Predator/prey relationships include lion and zebras, eagles and mice, osprey and fish, robins and worms, frogs and insects, baleen whales and zooplankton.
A community is composed of interacting populations of organisms in a given area, and an ecosystem is composed of interacting groups of organisms and their physical environment.
Humans raising cattle for food is technically a form of predation. Humans are secondary consumers feeding on the cattle which are primary consumers feeding on the plants which are primary producers. It could be argued however, that it is a type of mutualistic relationship in which both populations benefit, because the cattle has been so changed that it cannot survive without human interaction.
Examples of herbivores include seed-eating birds, deer, rabbits, and zooplankton. Examples of carnivores include wolves, falcons, and sharks. Examples of omnivores include humans, bears, and raccoons.
Trophic levels in an ecosystem include producers, herbivores, carnivores, omnivores, and decomposers.
In the carbon cycle, plants incorporate carbon into organic molecules through the process of photosynthesis. The organic molecules in plants are consumed by herbivores and the molecules are further passed on to carnivores. Decomposing-organisms convert organic carbon waste and dead organisms into inorganic carbon during respiration.
In the nitrogen cycle, atmospheric nitrogen is converted by nitrogen-fixing bacteria into a form that plants use to make proteins and other compounds. These compounds are passed to consumers. Decomposers convert dead organisms and waste into ammonia which is reused by plants.
In the phosphorous cycle, phosphate found in rock dissolves and becomes available to plants which are then eaten by consumers. The phosphate is recycled by decomposers and leaching from waste into the soil.
The major biotic factors in an aquarium are light, temperature, salinity, dissolved oxygen, and nutrients. The biotic factors include all of the living organisms in the aquarium. Producers include aquatic plants, algae, and possibly photosynthetic bacteria. Primary consumers include snails, protozoans, small crustaceans, and plant-eating fish. Secondary consumers include larger fish. Decomposers include bacteria and fungi.
