is a group of populations of different species living close
enough to interact.
•Concept 54.1: Community interactions are classified by whether they help, harm, or
have no effect on the species involved
•Ecologists call relationships between species in a community interspecific interactions
•Examples are competition, predation, herbivory, and symbiosis (including mutualism,
paratism, and commensalism.
•Interspecific interactions can affect the survival and reproduction of each species, and
the effects can be summarized as positive (+), negative (–), or no effect (0)
(–/– interaction) is an interaction that occurs when
individuals of different species complete for a resource that limits their growth and
•Strong competition can lead to
, a local elimination of the inferior
•The competitive exclusion principle states that two species competing for the same
limiting resources cannot coexist in the same place
•The total of a species’ use of biotic and abiotic resources is called the species’ ecological
•An ecological niche can also be thought of as an organism’s ecological role
•Ecologically similar species can coexist in a community if there are one or more
significant differences in their niches
Resource partitioning –
the differentiation of niches that enables similar species to
coexist in a community.
•As a result of competition, a species’ fundamental niche, the niche potentially occupied
by that species may differ from its realized niche, which is actually being occupied.
Character displacement –
the tendency for characteristics to diverge more in sympatric
populations of two species than in allopatric populations of the same two species.
•An example is variation in beak size between populations of two species of Galápagos
(+/– interaction) – one species, the predator, kills and eats the other, the prey
•Some feeding adaptations of predators are claws, teeth, fangs, stingers, and poison
•Prey display various defensive adaptations
•Behavioral defenses include hiding, fleeting, or forming herds or schools
•Animals also have morphological and physiological defense adaptations
, or camouflage, makes the prey difficult to spot.
•Animals with effective chemical defense often exhibit bright warning coloration, called
•Predators are particularly cautious in dealing with prey that display such coloration