21.3 Interactions among living things pg 722• Key concepts: How do an organism’s

adaptations help it to survive?• What are the major ways in which

organisms in an ecosystem interact?• What are the three types of symbiotic

relationships?• Key terms: natural selection,

adaptations, niche, competition, predation, predator, prey, symbiosis, mutualism, commensalism, parasitism, parasite, host

Adapting to the environment

• Natural Selection – a process that selects individuals better suited to their environments to reproduce. It results in adaptations.• Adaptations – the behaviors and physical characteristics that allow

organisms to live successfully in their environments.

• Individuals who are poorly suited to the environment are less likely to survive and reproduce.

Niche• Every organism has a variety of

adaptations that are suited to its specific living conditions. • The role of an organism in its

habitat is its niche. • Includes type of food, how it gets

food, which others use the same food• Also includes how and when the

organism reproduces and the physical conditions it needs to survive

Competition• There are three major types

of interactions among organisms: competition, predation, and symbiosis• Competition is the struggle

between organisms to survive as they attempt to use the same limited resource (food, water, shelter)

Predation• An interaction in which one organism kills another for food. • Predator – does the killing• Prey – gets killed

• Effect of predation on population size: if there are many predators, a decrease in prey population will occur. When that happens, the predators will die from lack of food.

Predator adaptations

• Speed, poisons, bigger eyes

Prey adaptations

• Speed, defensive mechanisms (smelliness, ability to puff up or pretend to be bigger, pretending to be a different species, etc)• Mimicry• False coloring• Camouflage• Protective covering

Symbiosis• Symbiosis is a close relationship

between two species that benefits at least one of the species• Three types occur: mutualism,

commensalism, parasitism

Mutualism

• Both species benefit• E.g. saguaro cactus and long-

eared bats• Bats get food and cactus gets

pollen transfer

Commensalism

• One species benefits and the other is not helped nor harmed• Red tailed hawk with saguaro cactus• Hawk gets a nest, cactus not affected

Parasitism• One organism living on or inside

another and harming it.• Organism that benefits is a parasite• Organism that is used is a host• Common parasites are ticks, fleas,

leeches

Please complete

• Page 729 section 3 assessment• 1abc, 2abc, 3abc