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Ecosystem Stability, Adaptive Cycles and Panarchy Slide 2 Slide 3 Slide 4 Slide 5 Temporal, spatial and structural features of complex system Amand et al. (2010) Slide 6 Tweets (social interactions) in Japan in response to the 2011 Tsunami have a scale-free pattern Slide 7 Ecosystem Stability Concepts Ecosystem stability: as the ability of an ecosystem to maintain its structure and function over long periods of time and despite disturbances. Resistance: ecosystem keeps its structure and continues normal functions even when environmental conditions change. Resilience: ecosystem eventually regains its normal structure and function after a disturbance. Slide 8 Resilience, the amount of energy that the system can absorb without leaving the cup for an alternative stability domain. Stability, the speed at which the ball returns to homeostasis; correlated with productivity Ball-and-cup model of system stability Ball=Current state of system Cup = Current stability domain Slide 9 Tundra: low stability, low resilience ICH: high stability, high resilience CWH: high stability, low resilience IDF: low stability, high resilience Slide 10 Managing ecosystems within the range of natural variability (RONV) RONV= resilience=range of possible locations of the ball within the cup Resilience: the capacity of a system to absorb disturbance and reorganise while undergoing change so as to still retain essentially the same function, structure, identity, and feedbacks. Management goal: make sure you stay in the cup and that it remains as wide and deep as possible Slide 11 Resistance: Ability of system to absorb small disturbances and prevent amplification Resilience: Ability of system to return to its original state Robustness: amount of disturbance system can absorb without flipping to alternative state Response: Magnitude of change Recovery: Extent of return to original state Ecosystem stability or response to disturbance depends on: Slide 12 Three types of change Tree cover % Precipitation drywet Precipitation drywet Precipitation drywet DryWet DryWet DryWet % Forest Cover Non-reversible Slide 13 Maintaining stability Species diversity is often the key to both ecosystem resistance and resilience. An ecosystem rich in biodiversity will likely be more stable than one whose biodiversity is low. Slide 14 Alive then dead: shifting stability domains Slide 15 Perrys cup vs peak models of system stability 1.Destabilization of ball depends on force (cup) versus type or foreignness (peak) of disturbance. 2.Ecosystem has plenty of warning (cup) for threshold disturbances versus surprises (falls off peak) (tipping points) 3.Ball movement in cup reversible once disturbance removed, but not once knocked off peak (domino effects common) 4.Cup model suggests equilibrium, but ecosystems are always in disequilibrium Slide 16 Adaptive cycle Potential: the number and kinds of future options available (e.g. high levels of biodiversity provide more future options than low levels) Connectedness: the degree to which a system can control its own destiny through internal controls, as distinct from being influenced by external variables Resilience: how vulnerable a system is to unexpected disturbances and surprises that can exceed or break that control. The adaptive cycle is the process that accounts for both the stability and change in complex systems. Slide 17 Gunderson & Holling 2002 Adaptive cycle of recovery (succession) after disturbance r=exploitation (disturbance, ruderale growth; stand initiation) K=conservation (carrying capacity, competition, niche specialization; stem exclusion) =release (self-thinning or gap disturbance, new opportunity, understory re-initiation) =re-organization (stratification of survivors, old-growth) Complex system undergoes change through adaptive cycle r K Slide 18 MetaphorEcologyBiologicalPsychologicalEconomic 1ExploitationBirthDevelopmentGrowth 2ConservationMaturitySanityConsolidate 3ReleaseDeathMadnessCollapse 4ReorganizationDecayHealingRebuild 1) Exploitation: rapid expansion, e.g., population grows. 2) Conservation: population reaches carrying capacity and stabilizes for a time. 3) Release: population declines due to a competitor, or changed conditions 4) Reorganization: certain members of the population are selected for their ability to survive despite the competitor or changed conditions that triggered the release. Four stages of adaptive cycle Slide 19 Adaptive cycle: four stages rK r K Slide 20 Slide 21 Mann et al. Chapman and Walsh Global to arctic Polar amplification Slide 22 Permafrost is thawing in many places, not just southern margins Slide 23 Schuur et al. 2008 Frozen peat, Canada, SiberiaCryoturbated soil, thin peat, AlaskaMineral deposit, Siberia Slide 24 Melting permafrost Hudson Bay, Canada Science Daily, Sept 2, 2008 Slide 25 What is panarchy? The term [panarchy] was coined as an antithesis to the word hierarchy (literally, sacred rules). Our view is that panarchy is a framework of nature's rules, hinted at by the name of the Greek god of nature, Pan. Lance Gunderson and C. S. Holling, Panarchy: Understanding Transformations in Systems of Humans and Nature, Island Press, p.21, 2001. Slide 26 Panarchy: all-encompassing nested system of adaptive cycles (Gunderson and Holling 2001). Slide 27 Panarchy in natural ecosystems Temporal scale Spatial scale Slide 28 7/10 These cycles connect with cycles above and below them in the hierarchy: Revolt" this occurs when fast, small events overwhelm large, slow ones, as when a small fire in a forest spreads to the crowns of trees, then to another patch, and eventually the entire forest Remember" this occurs when the potential accumulated and stored in the larger, slow levels influences the reorganization. For example, after a forest fire the processes and resources accumulated at a larger level slow the leakage of nutrients, and options for renewal draw from the seed bank, physical structures and surrounding species that form a biotic legacy. Slide 29 There are discontinuities in variables of interest Discontinuities determine dominant scales Slide 30 Panarchy predicts discontinuities in adaptive cycles across scales Slide 31 Summary Complex adaptive systems are inherently stable Stable systems change but are homeostatic, like a dancer Stables systems have resistance, where small disturbances are contained, and resilience, where the system returns to the same stability domain Complex systems change through adaptive cycles Adaptive cycles and panarchy are stabilizing characteristics Positive feedbacks and crossing tipping points can lead to loss of stability Climate change could cause instability Maintaining complexity will be crucial Slide 32 Melting permafrost Hudson Bay, Canada Science Daily, Sept 2, 2008 Slide 33 Slide 34 Slide 35 Slide 36 Slide 37