Predation and Food Webs

• herbivory is divided into consumption of macrophytes or microscopic algae
• phytoplankton are mainly consumed by invertebrates and fish
• Periphyton are mainly consumed by numerous macroorganisms
• What effects of grazing on periphyton does it have on structure?

  decrease in biomass, change in composition, form, richness and diversity
• what effects of grazing on periphyton does it have on function?

  decrease primary production, increase constant production , rate of nutrient cycling, rate of export of cells from assemblage
• detritus is the base of the food web in the following:

  • benthic areas
  • small forested streams
  • wetlands
• many organisms occupy different trophic levels depending on life stage
• what are the four types of defenses?

  • mechanical (size, protective structures)
  • chemical (toxins, low nutritional value)
  • Life history (altered timing of reproduction)
  • Behaviour (avoidance)
• Bottom-up -> primary production is controlled by abiotic factors
• Top-down -> primary production is controlled by predators in upper trophic levels
• herbivory -> controls structure and function of primary producers
• detrivory -> base of food web in some ecosystems