Relationships Between Populations Symbiosis: a relationship in which two organisms LIVE closely together Mutualism: when both organisms benefit + + Commensalism: when one organism benefits and the other is neither helped nor harmed + o Parasitism (Parasite-host): when one organism benefits and the other is harmed + - Predation (not a symbiotic relationship) Predator: does the eating Prey: organism that is eaten

Predator-Prey Populations Predator-Prey Populations Predator-prey graphs go up and down like a seesaw (teeter-totter). In 1975, which population is higher, the wolf population or the moose population? Video on Predators and Prey

Predation and Evolution Prey populations have high pressure from natural selection. Adaptations that increase survival are favored: needles on cacti, spines on sea urchins, poisonous skin secretions on frogs, evasion behaviors. In turn, adaptations that provide predator advantage are favored: claws, stronger beaks on birds for cracking hard shells.

Prey Protection: how prey protect themselves from predators Warning coloration Camouflage Mimicry

Warning Coloration Brightly colored or patterned animals are usually poisonous. Their bright colors are a warning to potential predators.

Camouflage An animal’s fur or skin blend in with its surroundings. Predators can more easily sneak up on prey. Prey are harder to find, and can evade predators.

Mimicry Animal looks like a more dangerous animal.