27: Food Web Ecology
Food chain
a linear representation of how different species in a community feed on each other
limited use
Food web
a complex and realistic representation of how species feed on each other in a community
Gut content analysis
evaluation of food items in animal guts
Stable isotope analysis
sample of tissue to determine C and N isotopes
C isotopes provide information about food resources
N isotopes provide information about trophic position
Trophic levels
a level in a food chain or food web of ecosystem
Primary consumer: a species that eats producers
Secondary consumer: a species that eats primary consumers
Tertiary consumer: a species that eats secondary consumers
Omnivore: a species that feeds at several trophic levels
Direct vs Indirect effects
Direct effect: an interaction between two species that does not involve other species
Indirect effect: an interaction between two species that involves one or more intermediate species
Trophic cascade: indirect effects in a community that are initiated by a predator
Thinking about food web interactions… Why is the world green?
Why plants are able to maintain so many leaves?
Why is the world green?
Green World Hypothesis
herbivores are kept in check by predators, parasites, disease
highlighted the importance of trophic interactions
Bottom-up control: when the abundances of trophic groups in nature are determined by the amount of energy available from the producers in a community
Top-down control: when the abundance of trophic groups is determined by the existence of predators at the top of the food web
Trophic cascades: indirect effects that propagate along the food web
Food chain
a linear representation of how different species in a community feed on each other
limited use
Food web
a complex and realistic representation of how species feed on each other in a community
Gut content analysis
evaluation of food items in animal guts
Stable isotope analysis
sample of tissue to determine C and N isotopes
C isotopes provide information about food resources
N isotopes provide information about trophic position
Trophic levels
a level in a food chain or food web of ecosystem
Primary consumer: a species that eats producers
Secondary consumer: a species that eats primary consumers
Tertiary consumer: a species that eats secondary consumers
Omnivore: a species that feeds at several trophic levels
Direct vs Indirect effects
Direct effect: an interaction between two species that does not involve other species
Indirect effect: an interaction between two species that involves one or more intermediate species
Trophic cascade: indirect effects in a community that are initiated by a predator
Thinking about food web interactions… Why is the world green?
Why plants are able to maintain so many leaves?
Why is the world green?
Green World Hypothesis
herbivores are kept in check by predators, parasites, disease
highlighted the importance of trophic interactions
Bottom-up control: when the abundances of trophic groups in nature are determined by the amount of energy available from the producers in a community
Top-down control: when the abundance of trophic groups is determined by the existence of predators at the top of the food web
Trophic cascades: indirect effects that propagate along the food web