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Exploiter-Victim Relationships Host-Parasite: Host death need not occur, and often does not; birth rate of host reduced by parasite Host-Parasitoid: Host death always occurs Predator-Prey: Death rate of prey increased by predators Herbivore-Plant: May resemble predation or parasitism

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Parasitoids

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Weevils and wasps

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Lynx and Snowshoe Hare

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Orange Mites, simple universe

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Orange Mites, increased patchiness

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Orange Mites, complex habitat

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Field Studies: Dingoes and kangaroos

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Dingoes and Boars

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Lamprey and Lake Trout

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Fox and Rabbit

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Plant-Herbivore

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Herbivore-- positive effect?

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N-fertilization effects

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Amboseli Elephants

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Elephants not excluded

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Elephants Excluded

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Baobab

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Baobab, Elephant Damage

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Functional Response Change in predator’s attack behavior as prey density increases Basic forms to consider: Type I: Linear increase in # attacked with increasing # prey (insatiable predator) Type II: Gradual levelling off As predators become satiated Type III: Predators satiable as in Type II, but hunt inefficiently at low prey densities # attacked/pred/time Prey density I II III

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Toxorhynchites

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Toxorhynchites brevipalpus

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Toxorhynchites Functional Response, sympatric & allopatric prey: NC (sympatric) IL (allopatric)

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Fraction killed per predator/time Type IType IIType III Prey Density Type II and III: satiable predators become less effective at controlling prey as prey become more abundant.

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Lotka-Volterra Predator-Prey Model: Assume: 1)Random search, producing encounters between prey and predators (and subsequent attacks) proportional to the product of their densities (attack rate = a’) 2)Exponential prey population growth in absence of predator, with constant growth rate, r 3)Death rate of predator is constant = q 4)Birth rate of predator proportional to #prey consumed

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Prey growth equation Prey: Without predator, dN/dt=rN If predator searches with attack rate a’, and there are C Predators, then deaths due to predation = a’CN dN/dt = rN - a’CN

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Predator Growth Equation dC/dt = (birth rate - death rate)C Death rate assumed constant = q Birth rate: #prey consumed x conversion constant, f = (#prey consumed)x f # prey consumed = a’CN (see prey equation) births = a’CNf birth rate = a’Nf dC/dt = (a’Nf - q)C

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Equilibrium Conditions, Prey Prey: dN/dt = rN - a’CN = 0 r-a’C = 0 C = r/a’ C N Too many predators Not enough predators

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Equilibrium conditions, predators dC/dt = (a’Nf - q)C = 0 a’Nf - q = 0 N = q/a’f C N More than enough prey Not enough prey

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Changes in both species: C N

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The prey curve has a hump

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Humped Prey curves Rotifer density Phytoplankton density Change in phytoplankton density at different combinations of Rotifer density and phytoplankton density

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Why the Prey curve has a Hump 1.Resource limits for prey at high densities (fewer preds needed to keep in check) 2.But, predator is most effective at low prey densities

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Effects of a humped prey curve: Increasing oscillation (unstable) Damped oscillation (stable point) Neutral stability C N

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Effects of a humped prey curve: Increasing oscillation (unstable) Damped oscillation (stable point) Neutral stability C N time

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