Biology 3445F Lecture 16: .docx
Document Summary
Recall: predation (+/-) is a direct interaction, direct interactions can give rise to indirect interactions, predation affects communities directly and indirectly. Strong negative correlation between the abundance of fish and ephemeral algae. Predator effect depended on presence of grazers (no effect on algae growth if not present) and habitat complexity (absence of canopy cover, ephemeral algae growth doubled) Integrated approach needed, looking at both bottom-up and top-down forces. Concept: changes in the abundances of organisms at one trophic level can influence energy flow at multiple. Green world hypothesis why is the world green? (hss, 1960) Simplified communities into 3 interacting trophic levels (producers, herbivores, predators) Proposed that populations in different trophic levels differ in their method of control: predators are controlled by competition, herbivores are controlled by predation, producers are controlled by competition. Not always supported . until support came from consumer-resource models. Explanations provided for derivations from hss by considering the number of trophic levels.
