SECTION 17.1COMMUNITY INTERACTIONS

EVOLUTION

Organisms in communities are adapted to live there by natural selection

Natural selection influences other organisms as well – this is coevolution

Coevolution leads to very complex interactions

COEVOLUTION

PREDATION

One organism kills another for foodThe predator is the killer, the prey is the

food

PREDATION

PARASITISM

One organism feeds on and lives on or in another

Parasites usually do not kill their hosts, but they can make them very sick

Many parasites have complex life cycles to transmit their offspring to another host

PARASITISM

HERBIVORESPlants cannot escape by moving, so they

have evolved other defensesSecondary compounds are not needed for

photosynthesis or to encourage insect pollination

They may be poisonous to insects or bad tasting

Some plants also have thorns or spikes

HERBIVORES

SYMBIOSIS

Two or more species living together long-term

Mutualism is helpful to bothCommensalism is helpful to only one, the

other is not helped or harmed

MUTUALISM

COMMENSALISM