1. KEY CONCEPT Organisms interact as individuals and as populations.

2. Competition and predation are two important ways in which organisms interact.
Competition occurs when two organisms fight for the same limited resource.
Intraspecific competition – involves 2 of the same species
Interspecific competition – involves 2 different species

3. Predation occurs when one organism captures and eats another.
Fig. Snakes are predators that swallow their prey whole. The hollow fangs of this timber rattlesnake inject venom to paralyze and kill its prey.

4. There are three major types of symbiotic relationships.
Mutualism: both organisms benefit
Fig. The lesser long-nosed bat eats the nectar from the cacti. The bat will eat the seeds of the Saguaro cacti. These indigestible seeds are dispersed to new locations as the bat flies across the desert.

5. Another mutualistic example:
Fig. Crocodile: Insects, parasites, and small pieces of food can get stuck in a crocodile's teeth and mouth. By helping to keep the crocodile's teeth clean, the plover provides a service to the fearsome reptile while acquiring nourishment for itself.

6. There are three major types of symbiotic relationships.
Commensalism: one organism benefits, the other is unharmed
Human Our eyelashes are home to tiny mites
that feast on oil secretions and dead skin. Without harming us, up to 20 mites may be living in one eyelash follicle.
Demodicids Eyelash mites find all they need to survive in the tiny follicles
of eyelashes. Magnified here 225 times, these creatures measure 0.4 mm in length and can be seen only with a microscope. +
Organism benefits Ø
Organism is not affected
Commensalism
(colored SEM; magnification 225 X)

7. There are three major types of symbiotic relationships.
Parasitism: one organism benefits, the other is harmed
Organism benefits _
Organism is not affected
Hornworm caterpillar
The host hornworm will eventually die as its organs are consumed
by wasp larvae.
Braconid wasp
Braconid larvae feed on their host and release themselves shortly before reaching
the pupae stage of development.
Parasitism +

8. There are three major types of symbiotic relationships.
Parasitism meet their needs as ectoparasites (such as leeches) and endoparasites (such as hookworms)
Fig. Many leeches feed on the blood of a host organism. Freshwater leeches such as this one can grow to lengths of 12 cm or more.
Fig. Hook worms are endoparasites with sharp teeth that attach to the intestinal wall of a host and absorb nutrients for food. (colored SEM, magnification 200X