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
No predators
Limited only by food
Herbivores
Producers

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

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

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

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 Cpredator > Pprey Prey controlled by predator If Cpredator < Pprey 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. Conditions for Trophic Cascades
3. Size-selective predation
alewife
From Brooks and Dodson 1965

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 