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Jon Abbatt (10)
Lecture 10

lecture 10 notes from prof. Thomson

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Jon Abbatt

Lecture 10: Tropic relationships in communities Trophic Level  Primary produced (autotroph): self-feeding , plants  Primary consumer: consumers of primary producers; herbivores from ants to zebras  Secondary consumers: carnivores who eats herbivores  Tertiary consumers: carnivores who eat secondary consumers  Detritivores: eat dead organic matters Food webs (Functional web)  Emphasizes the influence of populations on growth rates in other populations.  Can only be revealed by experiments Control experiment Insecticide treatment Beetles abundant Beetles suppressed High plant diversity Low plant diversity Beetle here are Keystone consumers because when they are removed, the edifice of the community tumbles  Interaction strengths are assessed by removal experiments. Trophic Cascades  Hairston, Smith & Slobodkin  Suggested that the earth is green because carnivores depress the populations of herbivores that would otherwise consume most of the vegetation.  Indirect effect: one trophic level exerts influences on a send by affecting a third. o Cascades involves effect that alternate across trophic levels. Top-down control: when higher trophic levels determine the sizes of the trophic levels below them. Bottom-up control: when the size of a trophic level is determined by the rate of production of its food resource. Experiment by Knight et al. (2005)  The presence of fish in a pond reduced the abundance of dragonfly larvae, which reduced the abundance of dragonfly adults, and thereby increased the abundance of pollinators and the number of seed produces by nearby plants  Adding fish to a pond improves the reproductive success of a plant on land. Difficulty of herbivory  Plant tissues are hard to convert into animal tissues o Cellulose and lignin tough, indigestible without microbial symbionts o Plant tissues heavily defended against herbivores, mechanically and chemically o Coevolutionary race between plants and insect herbivores is responsible for much of biodiversity; specialization is common. Milkweeds vs. Monarch butterfly larva  Milkweeds contains repellent latex under pressure in leaf veins (poisonous)
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