BIO120H1 Lecture Notes - Lecture 10: Detritivore, Herbivore, Lignin

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11 Nov 2012
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Lecture 10: Trophic relationships in communities
Trophic eco = who eats what?
Flow of energy through food
Plants don’t eat anything, but sunlight
Organisms came up with defensive mechanisms to not be eaten to boost up their fitness
Trophic levels based on the function in the trophic flow in the whole community
- Primary Producers = plants
- Primary consumers = herbivores(insects)
- Secondary consumers = carnivores who eat herbivores
- Tertiary consumers = carnivores who eat secondary consumers
- Detritivores = eat dead organic matter
Food chain and food webs
- Trophic connections among species can be analyzed as interaction webs with network
properties like ‘connectance’. Getting idea from internet web.
- If we have a lot of organisms who eat each other we get a food web
- Trophic relations can determine community structure in ways that can be investigated by
removal experiments
Interaction strengths are assessed by removal experiments. Think of tomato experiment from the lab:
control group and insecticide treatment
Example from the lecture:
Control treatment
Insecticide treatment
Beetles abundant
Goldenrod beetles suppressed
High plant diversity
Low plant diversity
Hairston, Smith & Slobodkin, 1960: trophic cascades (HSS)
Proposition: by just looking at the world we can understand how tropic levels are connected
- The world is green: plants are not being limited by herbivores, because of the indirect effect of
carnivores eat the herbivores, thus, not controlled by food supply, but by predation.
- Indirect effect: one trophic level exerts influence on a second by affecting a third
- Cascades involve effects that alternate across trophic levels
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Document Summary

Organisms came up with defensive mechanisms to not be eaten to boost up their fitness. Trophic levels based on the function in the trophic flow in the whole community. Tertiary consumers = carnivores who eat secondary consumers. Trophic connections among species can be analyzed as interaction webs with network properties like connectance". If we have a lot of organisms who eat each other we get a food web. Trophic relations can determine community structure in ways that can be investigated by removal experiments. Think of tomato experiment from the lab: control group and insecticide treatment. Hairston, smith & slobodkin, 1960: trophic cascades (hss) Proposition: by just looking at the world we can understand how tropic levels are connected. The world is green: plants are not being limited by herbivores, because of the indirect effect of carnivores eat the herbivores, thus, not controlled by food supply, but by predation.

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