BIOLOGY 1B Lecture Notes - Lecture 6: Sine Wave, Paramecium, Herbivore
12 Jun 2018
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Lecture 6
10/06
• Predation: an interaction in which the predator kills and eats the prey
o Predators can strongly affect species distribution and abundance
▪ Removing predator- burst in prey population
• Herbivory: an interaction in which an organism eats parts of a plant of alga but does not kill it
• Parasitism: an interaction in which one organism- the parasite- derives nourishment form another-
the hose, which is harmed in the process. Parasites are smaller than the hose and live on or in the
host’s body
• Paramecium-Didinium
o Paramecium affects the didinium population
▪ Both go extinct
• Positive negative
o Not stable
o Small area- predator eats all prey then goes extinct
• Gave paramecium a refuge- prey doenst go extinct; predator (p) can hide
in refuge
• Lynx-hare
o Prey population peaks before predator population
o Dn/dt of predator is positive because its eating the prey, prey is negative because its being
eaten
o Oscillating sine wave
▪ Oscillations are not in sync
▪ Why does predator peak after prey?
• Increase of predator causes prey to decline
• Why 1/4th phase stagger?
o When there’s still some food around, the predator population can
peak
o When predator is at low abundance, prey is increasing (and vica
versa)
o When prey is at high abundance, predator is increasing (and vica
versa)
• Refuges for prey help to stabilize predator-prey interactions
• Mite empirical system
o Refuges for prey help to stabilize predator-prey interactions
o Too many oranges, mite would kick off and explode
o Predator mite as well
o Structural complexity of experiment
o Results:
▪ Predator drives prey extinct
▪ Sin wave
▪ Predator peaked after prey in more complex experiment
o Refuge effect- prey hiding from predator
• Prey switching can stabilize as well
• Time lags make model more complex
• Defenses against predation
o Avoid, escape, defend
o Camouflage, flight, fight
o Physical defenses: spines, pufferfish, turtle shell, fuzzy hairs on plants (trichoma)
o Chemical defenses: poison, skunk
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