Why do organisms interact? Within an environment, there are limited resources to be used Many organisms share a habitat. Habitat = the actual area in the ecosystem where an organism lives, including all of its abiotic and biotic resources. EACH ORGANISM HAS A UNIQUE NICHE!! Niche = all of the things an organism needs and does within its habitat.

Predation One animal kills and eats another for food Predator = Organism hunting/killing another for food Prey = Organism killed/consumed as food Examples? A predator/prey graph shows the cycling of populations over time.

What is happening at points A and B? Predation What is happening at points A and B? A B

Competition Competition is a relationship that exists between two or more organisms that are fighting for the same limited resource. Competition can come in two forms: Interspecific Competition- where competition is occurring between different species. (Think international) Intraspecific Competition- where competition is occurring within the same species. (Think intramural)

Competitive Exclusion Principle No two organisms can occupy the same niche at the same time. If the organisms are very different, one is probably a better fit than the other If the organisms are similar, it will take a fight to see who will win. The loser will have to find a different niche to occupy. Ex. LION KING Lion King Example: Mufasa and Simba’s dad fight to be king of the pride – Mufasa wins and dad dies. Then Simba and Mufasa compete for the same niche again (king of the pride.) Loser (Mufasa) is excluded

Symbiosis Any interaction that involves a close, physical, long term relationship between two species One species ALWAYS benefits ALWAYS interspecific (between two different species)

Symbiotic Relationships: Parasitism One organism (parasite) benefits from the relationship, while the other organism (the host) is harmed. Examples? Ex. Ticks on a dog

Symbiotic Relationships: Parasitism It is crucial in parasitic relationships that the parasite not kill the host. Why? For a parasite-host relationship to persist, each population must not have a devastating effect on the other. The parasite must allow the host to live long enough for the parasite to survive and spread. Ex. Fleas on a cat

Symbiotic Relationships: Commensalism One organism is benefitted while the other is unaffected (neither benefitted nor harmed). Examples? Ex. Barnacles on mussels

Symbiotic Relationships: Mutualism Both organisms involved benefit. Helps both organisms survive. Examples? Ex. Clownfish and anemone