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Holling 1973

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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

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Disseminating the science of BarEcoRe StateProcess Engineering viewEcosystem view Predictable perturbationsUnpredictable perturbations (one) equilibriumMany possible states Analytical studyNot amenable to analytical study Inheritance from physical scienceNo inheritance from physical science 2 views of the world 1 empirical evidence Populations are highly variable and therefore more often far from equilibrium rather than near it

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Disseminating the science of BarEcoRe Some theory Predator-prey models Stable equilibrium Stable limit cycle … Models inspired from isolated systems in physics. They lack 4 elements that are found in real systems: 1.Multiplicity of components 2.Complex (non-linear) processes 3.Spatial and temporal processes 4.Stochasticity (randomness) Do conclusions derived from such models remain valid if these elements are considered?

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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.

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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.

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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

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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… Stabilitypersistence (~resilience)

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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.

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Disseminating the science of BarEcoRe Resilience versus stability Highly dynamic environmentRelatively stable environment Ecosystems have evolve to cope with variable environment Ecosystems have evolve to cope with stable environment High resilienceLow resilience High variabilityLow 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

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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

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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.

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