Abiotic Factor - A non-living feature of an ecosystem (rock, water, sun, etc.) Biodiversity - the variety of life in the world or in a particular ecosystem or habitat Biotic Factor - A living feature of an ecosystem (plants, animals, leaves, etc.) Carbon Cycle - the transfer of carbon through naturally occurring processes between organisms and the environment Coexistence - the living together of two organisms or species in the same habitat without trying to eliminate the other Commensalism - an association between two organisms in which one benefits and the other derives neither benefit nor harm. Competition - an interaction between organisms or species for resources - food, shelter, etc. Consumer - an organism that obtains energy from feeding on another organism Decomposer - organisms that break down waste and the remains of other organisms to return the raw materials back to the ecosystem Density-dependent factor - The tendency for the death rate in a population to increase, or the birth or growth rate to decrease, as the density of the population increases Density-independent factor - The tendency for the death, birth or growth rate in a population neither to rise nor fall as the density increases Ecological Pyramid - models that show how energy flows through ecosystems Food Chain - the order in which matter and energy in the form of food is transferred from one organism to another Food Web - a network of food chains or feeding relationships Mutualism - a relationship between two species of organisms that both benefit from the relationship Nitrogen Cycle - a continuous series of natural processes by which nitrogen passes successively from air to soil to organisms and back to air or soil Parasitism - a relationship between two organisms in which one benefits or lives off the other Population - a group of individuals of one species in an area Predation - an interaction between species in which one species (the predator) eats the other (the prey) Producer - an organism that can make its own food Trophic Level - each level in the transfer of energy through an ecosystem Water Cycle - the continuous movement of water on, above, and below the Earth’s surface