Stability in Natural Systems


Stability in Natural Systems-

Biodiversity=dynamic- it can change over time

Ecosystems can change composition/state- What can cause this?

Stability dimensions

  • Resilience
  • Resistance
  • Local stability
  • Global stability

Resilience- abilility to bounce back after a disturbance- measured as return time to equilibrium  e.g. Wils corals recover from bleaching after El Nino years and if so how long will this take?

Resistence-ability of systems to withstand different pressures without changing-magnitude of pertubation required to change the population.

Local stability- ability of a system to return to its original equilibrium position following a small perturbation-population changes only locally.

Global stability- ability of a system to return to its orginal equilibrium following a large scale pertubation- population changes globally.

Traditional management views=Nature is globally stable- systems have evolved to be able to return to equilibriums when disturbance stops. Numbers recover.

However some systems do not show this stability-some populations, communities or ecosystems may return to a different equilibrium state/alternate state. 

Evidence for this? Paine's starfish experiment in the N.E. Pacific: When starfish were removed- lots of species decreased as mussels increased. When starfish were put back- things dont change for a short period of time- mussels are too big for starfish to eat. Ecosystem has shifted into alternative mussel-dominated state. Would not continue indefinitely however- harder mussels will eventually die of old age. Young juvenile mussels will be preyed upon by starfish- may take 10/15 years for system to return to normal.

Observations on succession- ecosystems appear to grow in complexity over time. e.g. Glacier Bay, Alaska- retreat of glacier by around 100km since 1800s. Bare soil-pioneer species (mosses + lichens)-grasses-trees. Web like food chains, high species diversity, narrow niche specialisation, large organisms, long/complex life cycles, k-selection, good stability.

Unstable/distressed systems move from mature to immature (more developed to less developed). Assessing the stafe of maturity estimates the


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