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TROPHIC CASCADES Elisa, Chelsea, Ellie. Trophic Cascades  Herbivores can limit plant populations, but…  In most places, plants are abundant and herbivores.

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Presentation on theme: "TROPHIC CASCADES Elisa, Chelsea, Ellie. Trophic Cascades  Herbivores can limit plant populations, but…  In most places, plants are abundant and herbivores."— Presentation transcript:

1 TROPHIC CASCADES Elisa, Chelsea, Ellie

2 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?

3 HSS hypothesis for why the world is green (Hairston, Smith, & Slobodkin, 1960)

4 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

5 Carnivores Herbivores Producers

6 Carnivores Herbivores Producers  No predators  Limited only by food

7 Carnivores Herbivores Producers  No predators  Limited only by food  Limited by predation

8 Carnivores Herbivores Producers  No predators  Limited only by food  Limited by predation

9 Carnivores Herbivores Producers  No predators  Limited only by food  Limited by predation  Limited by competition and resources

10  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

11 CONDITIONS FOR TROPHIC CASCADES 1. Consumers can control biomass of prey

12 CONDITIONS FOR TROPHIC CASCADES If C predator > P prey Prey controlled by predator If C predator < P prey Prey not be controlled by predator P = production C = consumption Bioenergetic budget G=growth (~ production) C=consumption R=respiration F=feces E=excreta

13 CONDITIONS FOR TROPHIC CASCADES 2. Simple and well-known food web

14 From Brooks and Dodson 1965 alewife CONDITIONS FOR TROPHIC CASCADES 3. Size-selective predation

15 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.

16 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

17 THE END!!! Elisa, Chelsea, Ellie Bye


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