Holling 1973

Disseminating the science of BarEcoRe

Article structure• Introduction

– Some theory

• Some real world examples– Self contained ecosystems– Process analysis– The random world– The spatial mosaic

• Synthesis– Some definitions– Resilience versus stability– Measurement

• Application

Disseminating the science of BarEcoRe

State Process

Engineering view Ecosystem view

Predictable perturbations Unpredictable perturbations

(one) equilibrium Many possible states

Analytical study Not amenable to analytical study

Inheritance from physical science No inheritance from physical science

2 views of the world

1 empirical evidencePopulations are highly variable and therefore more often far from

equilibrium rather than near it

Disseminating the science of BarEcoRe

Some theory

Predator-prey modelsStable equilibriumStable limit cycle…

Models inspired from ‘isolated systems’ in physics. They lack 4 elements that are found in real systems:1.Multiplicity of components2.Complex (non-linear) processes3.Spatial and temporal processes4.Stochasticity (randomness)

Do conclusions derived from such models remain valid if these elements are considered?

Disseminating the science of BarEcoRe

Self-contained ecosystems

• Search for real system that are simple• Lakes: isolated, simple controls:

nutrients & fishing• Empirical evidence for multiple stable

states and rapid transitions ≠ equilibrium point or limit cycle.

Disseminating the science of BarEcoRe

Process analysis

• Ricker demographic models• + realism based on empirical evidence

of predation processes• -> complex models with multiple stable

points• Ecological conclusions from models with

simplified processes are different from those from more realistic models and…evidence for multiple stable states ≠ equilibrium point or limit cycle.

Disseminating the science of BarEcoRe

The random world

• Examples with budworms and pink salmon

• Transitions between different regimes triggered by random climate fluctuations

• Support for multiple stable states & important role of variable (random) external forcing

Disseminating the science of BarEcoRe

The spatial mosaic

• Spatial processes, i.e. dispersion and limits to dispersion modify prey-predator dynamics

• Spatially structured populations can persist while fluctuating greatly at local scale.

• Ecological conclusions from models with spatial processes are different from those from more realistic models and…

• Stability≠persistence (~resilience)

Disseminating the science of BarEcoRe

Some definitions

“I propose that the behavior of ecological systems could well be defined by two distinct properties: resilience and stability.

Resilience determines the persistence of relationships within a system and is a measure of the ability of these systems to absorb changes of state variables, driving variables, and parameters, and still persist. In this definition resilience is the property of the system and persistence or probability of extinction is the result.

Stability, on the other hand, is the ability of a system to return to an equilibrium state after a temporary disturbance… In this definition stability is the property of the system and the degree of fluctuation around specific states the result.”

Disseminating the science of BarEcoRe

Resilience versus stabilityHighly dynamic environment Relatively stable environment

Ecosystems have evolve to cope with variable environment

Ecosystems have evolve to cope with stable environment

High resilience Low resilience

High variability Low variability

“…some Arctic ecosystems thought of as fragile may be highly resilient, although unstable.”

Stability-complexity debate (May, 1972)

Needs to be considered for systems with multiple equilibriums and for transitory dynamics

Disseminating the science of BarEcoRe

Measurement

• Stability: standard mathematical tools, close to equilibrium

• Resilience: probability of extinction, far from equilibrium– Suggestion to use negative binomial

distribution

Disseminating the science of BarEcoRe

Application• Implication for management:

“A management approach based on resilience … would emphasize the need to keep options open, the need to view events in a regional rather than a local context, and the need to emphasize heterogeneity. Following from this would be not the presumption of sufficient knowledge, but the recognition of our ignorance; not the assumption that future events are expected, but that they will be unexpected.

The resilience framework can accommodate this shift of perspective, for it does not require a precise capacity to predict the future, but only a qualitative capacity to devise systems that can absorb and accommodate future events in \whatever unexpected form they may take.”