Stability, regime shifts, and alternative stable states

What is temporal stability?

Variance in abundance/biomass over time

How can diversity affect stability?

• Increasing species abundance/biomass

• Decreasing summed variance

• Decreasing summed covariance

What is the portfolio effect?

• Diversity effects on the temporal stability of an ecosystem service due to the independent dynamics of species that perform a similar service

• The degree to which diversity reduces variability in a service

• Analogous to the effects of asset diversity on the stability of financial portfolios

• Associated with species diversity in a community or subpopulation diversity within a metapopulation

• Requires that species or subpopulations respond differently to environmental variation

What is a regime shift?

A change from one community state to another

What is a tipping point?

The critical threshold at which a system undergoes a regime shift

What are alternative stable states?

Dramatic changes in community state from one stable configuration of species composition and food web structure to another

What is a hysteresis loop?

The delayed response to forward and backward changes in environmental conditions creates a loop where alternative stable states are possible

What did Connell and Sousa propose about the evidence required for alternative stable states?

• Community must have an equilibrium point

• If perturbed sufficiently, the community moves to a second equilibrium, where it remains after the disturbance has disappeared

• Abiotic environments must be the same

• Alternate states must persist for more than one generation

What did Peterson propose about the evidence required for alternative stable states?

A single site can be occupied by 2 or more self-replacing communities

What does Scheffer proposed about the evidence required for alternative stable states?

The existence of hysteresis loops