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Lecture 23

BIO120H1 Lecture Notes - Lecture 23: Detritivore, Ecological Network, Theobromine


Department
Biology
Course Code
BIO120H1
Professor
Spencer Barrett
Lecture
23

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BIO120H1(F) Lecture 23 Wednesday, November 29, 2018
Primary producers = plants
Primary consumers = herbivores
Secondary consumers = carnivores who eat herbivores
Tertiary consumers = carnivores who eat secondary consumers
Detritivores eat dead organic matter
Trophic connections among species can be analyzed as interaction webs with network
properties like oetae
More importantly, trophic relations can determine community structure in ways that can be
investigated by removal experiments
An experiment:
Control experiment abundant beetles + high plant diversity
Insecticide treatment goldenrod beetles suppressed + low plant diversity
Hairston, Smith & Slobodkin (1960) trophi asades
The orld is gree eause ariores keep do heriores so that heriores do’t
limit plant growth
Example of an indirect effect: one trophic level exerts influence on a second by affecting
a third
Cascades involve effects that alternate across trophic levels
Can drastically affect communities
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BIO120H1(F) Lecture 23 Wednesday, November 29, 2018
An experiment:
Question: Will lizards benefit plants or not?
Lizards eat spiders
Lizards eat herbivores
Spiders eat herbivores
Herbivores eat plants
Trophic cascades likely, ut a’t aser fro topology of the food
web alone, so must do experiments!
energy web
Answer: Lizards do benefit plants because of unequal interaction strengths
Lizards eat spiders
Lizards eat herbivores
Spiders eat herbivores
But the effect of lizards on spiders is weak, while their effect on herbivores is strong
So, lizards reinforce, rather than counteract, the effects of spiders, but it could have
gone the other way!
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BIO120H1(F) Lecture 23 Wednesday, November 29, 2018
Another experiment:
Far-reaching effects of fish in ponds
NOTE:
Solid lines = direct effects
Broken lines = indirect effects
Some results:
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