biodiversity The diversity of plant and animal life in a particular habitat (or in the world as a whole).

ecosystems A system that includes all living organisms (biotic factors) in an area as well as its physical environment (abiotic factors) functioning together as a unit.

limiting factor A factor present in an environment that controls a process, particularly the growth, abundance or distribution of a population of organisms in an ecosystem.

ecological niche The ecological role and space that an organism fills in an ecosystem.

Adaptation The adjustment or changes in behavior, physiology, and structure of an organism to become more suited to an environment.

competition A symbiotic relationship between or among living things for resources, such as food, space, shelter, mate, ecological status, etc.

predation A form of symbiotic relationship between two organisms of unlike species in which one of them acts as predator that captures and feeds on the other organism that serves as the prey.

symbiosis The relationship between two different species of organisms that are interdependent on each other.

commensalism A form of symbiosis between two organisms of different species in which one of them benefits from the association whereas the other is largely unaffected or not significantly harmed or benefiting from the relationship.

mutualism A symbiotic relationship between individuals of different species in which both individuals benefit from the association.

parasitism A form of symbiosis in which one organism (called parasite) benefits at the expense of another organism usually of different species (called host). The association may also lead to the injury of the host.

food chain A feeding hierarchy in which organisms in an ecosystem are grouped into trophic (nutritional) levels and are shown in a succession to represent the flow of food energy and the feeding relationships between them.

food web A food web is many food chains linked together to show a more accurate model of all possible feeding relationships of organisms in an ecosystem.

energy pyramid A graphical model that is shaped like a pyramid to show how the energy flows through a food chain, how the amount of energy is decreasing and becoming less available for organisms as it enters each trophic level, and how much of the energy in the ecosystem is lost to the atmosphere as heat.