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In ecology, resilience is a property of an ecosystem which characterises ecosystem behaviour in relation to a perturbation. In order for ecosystem resilience to be defined, the ecosystem must have some sort of stability prior to the perturbation. Resilience cannot be defined for an ecosystem if this condition is not met. The requisite stability is often approximated as a single steady state or cyclic state of the ecosystem variable(s) of interest, such as for example the population(s) of key economically exploitable species. Resilience relates to return to stability following perturbation. The precise relationship between resilience and return to stability depends on the definition of resilience which is used.
The concept of resilience in ecological systems was first described by the Canadian ecologist C. S. Holling  in order to draw attention to tradeoffs between efficiency on the one hand and persistence on the other, or between constancy and change, or between predictability and unpredictability.
Resilience is defined as "the capacity of an ecosystem to tolerate disturbance without collapsing into a qualitatively different state that is controlled by a different set of processes. A resilient ecosystem can withstand shocks and rebuild itself when necessary. Resilience in social systems has the added capacity of humans to anticipate and plan for the future." Resilience is conferred in human and ecological systems by adaptive capacity.
When a system can reorganize, that is shift from one stability domain to another, a more relevant measure of ecosystem dynamics is ecological resilience. It is a measure of the amount of change or disruption that is required to transform a system from being maintained by one set of mutually reinforcing processes and structures to a different set of processes and structures.
Resilience is also defined a second way, i.e. the rate at which a system returns to stability following perturbation. Unlike the previous definition, this definition of resilience assumes that behavior of a system remains within the stable domain that contains this steady state.
As initially outlined by Brian Walker, there are four main aspects of resilience including latitude, resistance, precariousness, and panarchy . These four dimensions are most easily understood through mathematical representation in phase space. A phase or state space diagram is one in which each axis represents a variable of a system with any number of variables, so a point in this space describes the system's total state. A state space diagram of an ecosystem would contain several attractors, or "basin of attraction" which are representations of ecosystem process configurations. Moreover, these configurations can change over time as a result of both internal and external processes.
Within a state space diagram, latitude describes the amount of change that the system's present configuration can absorb before switching over to a different attractor. Resistance is a measure of the degree of difficulty in changing from one attractor to another. Precariousness is the instantaneous trajectory of the system, which can be used as an estimation of whether the system will switch attractor. Panarchy is the degree to which a certain hierarchical level of an ecosystem is influenced by other levels. For example, organisms living in communities that are in isolation from one another may be organized differently than the same type of organism living in a large continuous population, thus the community-level structure is influenced by population-level interactions.
Resilience, vulnerability, adaptive capacity
Within Social Ecological Systems (SESs) there is often the need for management. The common desire of all managers is to decrease risk. The two ways of decreasing risk in SESs are by decreasing vulnerability and increasing resilience. Although the two are related, they have important differences. A system is vulnerable to change if its current configuration can't handle change. Vulnerability is therefore based in the history of the system and the direction of change. Adaptive capacity is the ability of actors within an SES to change the resilience of the system. Thus, within an SES that is experiencing a decrease in weather predictability due to climate change, adaptive capacity would be the ability of people to change their transportation and communication systems to cope with the change.
- Resilience Alliance - a research network that focuses on social-ecological resilience
- "Resilience, adaptability and transformability" - a concise article coauthored by Walker, Holling, Carpenter and Kinzig outlining the three inter-related attributes of systems that determine their capacity to respond to external shocks.
- Stockholm Resilience Centre - an international centre that advances transdisciplinary research for governance of social-ecological systems with a special emphasis on resilience - the ability to deal with change and continue to develop.
- Microdocs: Resilience
Human (psychosocial) perspectives have also entered the interdisciplinary and cross-sector discourse on resilience as a dynamic process of adaptation and transformation in the face of adversity. Resilience is defined as a multidimensional construct that refers to "the capacity of individuals, families, communities, and systems or institutions (formal and informal)to anticipate, withstand and/or judiciously engage with catastrophic events and/or experiences, actively making meaning of adversity with the goal of maintaining 'normal' function without fundamentally losing their identity."  In this context, resilience is understood as much more than the absence of Post Traumatic Stress Disorder (PTSD), and measured, at least in part, using the "Sense of Coherence" (SOC) scale across scales and culture/language boundaries.
- ^ C.S. Holling. 1973. "Resilience and stability of ecological systems". in: Annual Review of Ecology and Systematics. Vol 4 :1-23.
- ^ B. Walker, C.S. Holling, S. R. Carpenter, A. Kinzig Resilience, 2004. "Adaptability and Transformability in Social–ecological Systems" Ecology and Society 9(2): 5. [online] URL: http://www.ecologyandsociety.org/vol9/iss2/art5/
- ^ http://www.tuftsgloballeadership.org/programs/irp
- ^ http://www.informaworld.com/smpp/content~content=a772441707~tab=send