KEY CONCEPT Organisms interact as individuals and as populations.

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

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.

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.

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.

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)

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 +

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