4.2 – Niches and Community Interactions

WHAT IS A NICHE?  Niche - the range of conditions in which a species lives and the way the species obtains what it needs to survive and reproduce.

TOLERANCE  Tolerance - ability to survive and reproduce under a range of environmental circumstances.  Every organisms has a tolerance range.

COMPETITION  Occurs when organisms attempt to use the same limited resource in the same place at the same time.

THE COMPETITIVE EXCLUSION PRINCIPLE  Direct competition between different species generally produces a winner and a loser.  Losing species dies out.  In the the experiment shown in the graph, two species of paramecia (P. aurelia and P. caudatum).  Grown separately and together.

 Intraspecific competition - occurring within one species  Interspecific competition - occurring between species COMPETITION AND PREDATION ARE TWO IMPORTANT WAYS IN WHICH ORGANISMS INTERACT.

DIVIDING RESOURCES  Instead of competing for similar resources, species usually divide them.  Example: the three species of North American warblers shown all live in the same trees and feed on insects.

PREDATOR-PREY RELATIONSHIPS  Interaction where one animal captures and feeds on another animal  This graph shows changes in predator and prey populations over time.

SYMBIOSIS  Any relationship where two species live closely together.

 There are three major types of symbiotic relationships. –Mutualism : Both organisms benefit!! (+,+)

–Commensalism: One organism benefits, the other is unharmed (+,O) 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 Ø Organism is not affected Commensalism

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 +

 Parasitism meet their needs as: Ectoparasites (such as leeches) Endoparasites (such as hookworms)