TROPHIC
CASCADES
Elisa, Chelsea, Ellie
Trophic Cascades
Herbivores can limit plant populations, but…
In most places, plants are abundant and herbivores
don’t limit plant growth
So…why is the world green?
HSS hypothesis for why the world is green
(Hairston, Smith, & Slobodkin, 1960)
WHY IS THE EARTH GREEN?
According to the HSS hypothesis the Earth is green
because there are carnivores…
Carnivores keep the herbivore population in check
which allows producers to keep producing
Carnivores
Herbivores
Producers
No predators
Carnivores
Herbivores
Producers
Limited only by food
No predators
Carnivores
Limited only by food
Limited by predation
Herbivores
Producers
No predators
Carnivores
Herbivores
Producers
Limited only by food
Limited by predation
No predators
Carnivores
Herbivores
Limited only by food
Limited by predation
Limited by competition and
Producers
resources
Trophic cascade – influence of producers or
consumers on species that are two or more
trophic levels away
Top-down Control – influence of predators on
the relative abundance of lower trophic levels
Bottom-up Control – influence of producers on
the relative abundance of higher trophic levels
CONDITIONS FOR
TROPHIC CASCADES
1. Consumers can
control biomass of
prey
CONDITIONS FOR
TROPHIC CASCADES
If Cpredator > Pprey
Prey controlled by predator
If Cpredator < Pprey
Prey not be controlled by
predator
Bioenergetic budget
G=growth (~ production)
P = production
C = consumption
C=consumption
R=respiration
F=feces
E=excreta
CONDITIONS FOR
TROPHIC CASCADES
2. Simple and well-known food web
CONDITIONS FOR TROPHIC CASCADES
3. Size-selective predation
alewife
From Brooks and Dodson 1965
WHAT IS BIODIVERSITY?
Biodiversity is the variability among living
organisms from all sources, including
terrestrial, marine, and other
aquatic ecosystems and the ecological
complexes of which they are part; this
includes diversity within species, between
species, and of ecosystems.
WHY IS IT IMPORTANT?
Biodiversity affects key ecosystem
processes in terrestrial ecosystems such as
biomass production, nutrient and water
cycling, and soil formation and retention—all
of which govern and ensure supporting
services
THE END!!!
Elisa, Chelsea, Ellie
Bye 