Thursday, October 25, 2007


Symbiosis: two or more kinds of organisms interact in often elaborate relationships

Types of Symbiosis
1. Competition (-/-): organisms compete for limited resources, when they compete there is less to go around for everyone
Example: Brown-Headed Cowbird & other birds' nest

2. Parasitism(-/+): one species benefits but the other is harmed
*parasites sometimes kill the host thus becoming predation
Example: tapeworm & human

3. Mutualism (+/+): both participating species benefit
Example: clown fish & anemone

4. Commensialism (+/0): one species benefits while the other neither benefits nor is harmed;
*it is often difficult to be certain whether or not the second partner receives a benefit or not, there is no clear cut boundary between commensalism & mutualism
Example: epiphyte

Animal Defense against Predators
Predation drives evolution
(provides strong selective pressure on both predator side and prey side)
Predator adaptations lead to prey adaptations

Predator adaptations: to locate & subdue
Ex: talons, speed, coloration, horns

Prey adaptations: to elude & defend
Ex: spines, thorns, coloration, & toxins

Cryptic coloration (blend in with background)
Aposematic coloration (bright warning to predators)

Batesian: harmless species mimics a harmful model
*convergent evolution: two species on different paths evolve to have the same

Mullerian: two or more protected species look like each other
*predators evolve an innate avoidance (group defense) like people to bees

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