Feedback Feedback loops Self regulation of natural systems

Feedback

Feedback loops • Self regulation of natural systems is achieved by the attainment of equilibrium through feedback systems • Change is a result of feedback loops but there is a time lag • Feedback occurs when one change leads to another change which eventually reinforces or slows the original change. • Or… • Outputs of the system are fed back into the input

Positive feedback • • • A runaway cycle – often called vicious cycles A change in a certain direction provides output that further increases that change Change leads to increasing change – it accelerates deviation Example: Global warming 1. Temperature increases Ice caps melt 2. Less Ice cap surface area Less sunlight is reflected away from earth (albedo) 3. More light hits dark ocean and heat is trapped 4. Further temperature increase Further melting of the ice

Solar radiation Energy in = Energy out Reflected by atmosphere (34%) Radiated by atmosphere as heat (66%) UV radiation Absorbed by ozone Lower stratosphere (ozone layer) Visible Greenhouse light Troposphere effect Heat Absorbed by the earth Heat radiated by the earth Earth

Negative feedback • One change leads to a result that lessens the original change • Self regulating method of control leading to the maintenance of a steady state equilibrium • Predator Prey is a classic Example – – – Snowshoe hare population increases More food for Lynx population increases Increased predation on hares hare population declines Less food for Lynx population declines Less predation Increase in hare population

Remember hare’s prey and other predators also have an effect

Most systems change by a combination of positive and negative feedback processes

Which of the populations show positive feedback? Which of the populations show negative feedback?

Positive or Negative? • If a pond ecosystem became polluted with nitrates, washed off agricultural land by surface runoff, algae would rapidly grow in the pond. The amount of dissolved oxygen in the water would decrease, killing the fish. The decomposers that would increase due to the dead fish would further decrease the amount of dissolved oxygen and so on. . . • A good supply of grass for rabbits to eat will attract more rabbits to the area, which puts pressure on the grass, so it dies back, so the decreased food supply leads to a decrease in population because of death or out migration, which takes away the pressure on the grass, which leads to more growth and a good supply of food which leads to a more rabbits attracted to the area which puts pressure on the grass and so on and on. .