BIO120H1 Lecture Notes - Lecture 23: Trophic Cascade, Keystone Species, Decomposer
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BIO120H1 Full Course Notes
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Tertiary consumers: carnivores who eat secondary consumers. Trophic connections among species can be analyzed as interaction webs (using statistics like connectance=proportion of possible links between species that actually occur) One species alters the effect another species has on a third. Interactions between two trophic levels cascade to a third. Carnivores keep population of herbivores down so herbivores don"t limit plant growth. Trophic cascades involve effects that alternate across trophic levels. Top-down: abundances kept low because of predation. Bottom-up: abundances kept low because of resource limitation. Keystone species shift communities between alternative states. Outcomes of trophic cascades depend on interaction strengths. Cellulose and etc. indigestible without microbial symbionts. Coevolutionary race between plants and insect herbivores responsible for much of biodiversity. Plant tissues hard to convert into animal tissues. Generalists can"t eat it, but specialists can. Plants evolve toxins to reduce herbivory, insects evolve detoxification or other mechanisms to overcome plant defenses. No plant species toxic enough to escape specialist herbivores.
