commensalism A relationship between two species in which one species benefits and the
other species is not harmed.
community All of the living creatures of an ecosystem; all of the populations of all of the
species that live together.
competition A rivalry between two species, or individuals of the same species, for the
same resources.
consumer An organism that does not create its own chemical energy, but uses other or-
ganisms for food.
decomposer An organism that breaks down the tissues of a dead organism into its various
components, including nutrients that can be used by other organisms.
ecosystem All of the living things in a region and the physical and chemical factors that
they need to live.
food chain An energy pathway that includes all organisms that are linked as they pass
along food energy, beginning with a producer and moving on to consumers.
food web Interwoven food chains that show each organism eating from different trophic
levels, which more closely reflects reality.
habitat Where an organism lives; habitats have distinctive features like climate or resource
availability.
herbivore An animal that only eats producers.
invertebrate Animals without backbones.
mutualism A symbiotic relationship between two species in which both species benefit.
niche An organism’s “job” within its community.
omnivore An organism that consumes both plants (producers) and other consumers (an-
imals) for food.