TROPHIC CASCADESElisa, 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

Carnivores

Herbivores

Producers

No predators Limited only by food

Carnivores

Herbivores

Producers

No predators Limited only by food

Limited by predation

Carnivores

Herbivores

Producers

No predators Limited only by food

Limited by predation

Carnivores

Herbivores

Producers

No predators Limited only by food

Limited by predation

Limited by competition and 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

P = productionC = consumption

Bioenergetic budget

G=growth (~ production)

C=consumption

R=respiration

F=feces

E=excreta

CONDITIONS FOR TROPHIC CASCADES

2. Simple and well-known food web

From Brooks and Dodson 1965

alewife

CONDITIONS FOR TROPHIC CASCADES3. Size-selective

predation

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