Feedbacks and biomanipulation

• critical transitions / tipping point

  • sudden change in (ecological) state due to relatively small change in external factors
  • result of strong internal feedback loops
  • difficult to get back in original conditions
  • difficult to predict/determine
• Positive feedback loop - albedo effect

  • ocean absorbs sun radiation, increasing temperatures, causing more ice to melt, which causes increase in ocean water and thus absorption of sun radiation
• turbidity caused by (1) abundant algae growth and (2) resuspension of particles

  • resuspension caused by either wind/current and species that stir up sediment from bottom
• assumption of the two alternative stable states model

  • turbidity increases with nutrients
  • vegetation decreases with turbidity
  • vegetation disappears when critical turbidity is reached
• two alternative stable states model depends on nutrient level

  • either plant dominated or algae dominated state
• hysteresis: current state depends on its history
• environmental conditions, competition, and predation are all important regulating mechanisms in aquatic systems
• cause-effect relationship not linear
• top-down control: predators limit species
• bottom-up control: limiting food availability
• allelopathy: phenomenon where plants excrete infochemicals to inhibit growth of other plants and phytoplankton
• clear water is prerequisite for successful plant growth

  • vegetation development has positive feedback loop