Stability in Natural Systems-
Biodiversity=dynamic- it can change over time
Ecosystems can change composition/state- What can cause this?
- 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…