Lecture XVII - Predation

Lecture XVII - Predation - Lecture XVII Species...

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Lecture XVII – Species interaction: Predation
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Species Interactions Species interactions can be divided into types, based on the effect that each has upon the other: Both negative (-,-) – competition Positive and positive (+,+) - mutualism Negative and neutral (-,0) or commensalism (+,0) – can relate to other organism (the one that is not being impacted) as environmental factor Negative and positive (+,-) – Exploitation, i.e., herbivory, predation, parasitoidism, parasitism Our focus is on Negative and positive (+,-) interaction
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Different Exploitative Relationships Kills prey: Predation Parasitoidism
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Predation Animal eats and kills more than one organism (fox eats mouse; deer eats seedlings)
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Parasitoidism Animal kill single animal or multiple animal kill single animal. Usually highly specialized on exploited species In the great majority of cases, the larvae of the parasitoid consumes the host species as it grows, either from the outside (parasitic wasps), or from the inside (ichneumon flies)
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Costs of Being Exploited Death Reduced growth Slow growth Less optimal behavior (ecology of fear) Lower population size Vulnerability to other factors (competition, disease, other predation)
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Theoretical Predator-Prey Dynamics Many species of animal show regular cycles of abundance (e.g., lemmings) In some cases, these cycles are mirrored by cycles of their major predator (snowshoe hare and lynx in Canada
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Parasitoid and Host Populations A moth ( Plodia ) and its wasp parasitoid ( Ventura ) cycle. Wasp larvae kill moth larvae. Without the parasitoid, the moth cycles, but at a much higher average density.
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Predator-Prey Cycles Along with competition, both Lotka and Volterra designed mathematical equations that attempt to develop a theoretical basis for these regular predator-prey cycles These cycles were expected to have a few characteristics: Prey populations show more intense fluctuations Predator cycles are delayed, relative to prey cycles
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Basic Model To begin with, we look at the prey population Basic exponential model: However, if we add loss to predators: c = predation rate (no. prey consumed by predator over unit time P = Predator population rN dt dN = cNP rN dt dN - =
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Basic Model If we assume that all the preys loss to predation goes into the reproduction of the predator Looking at the predator dynamics: δP = death rate of predators a = Conversion efficiency of prey biomass to predator young biomass ( 29 P cNP a dt dN δ - =
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Predation Model If we look at number of prey at equilibrium, i.e., dN prey /dt = 0, then: And: So: 0 = - cNP rN cNP rN = c r N =
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Predation Model If we look at number of predators at equilibrium, i.e., dP/dt = 0, then: And: So, at equilibrium: ( 29 0 = - pred N cNP a δ ( 29 P cNP a = ac N =
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Lotka-Volterra Predator-Prey Cycles Reiterate - prey rate of change = prey population growth - losses due to
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Lecture XVII - Predation - Lecture XVII Species...

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