A system is a network of interdependent components and processes, with materials and energy flowing from one component of the system to another. A simple system consists of state variables (also called compartments), which store resources such as energy, matter, or water; and flows, or the pathways by which those resources move from one state variable to another. Open systems are those that receive inputs from their surroundings and produce outputs that leave the system. Almost all natural systems are open systems. In principle, a closed system exchanges no energy or matter with its surroundings, but these are rare. Pseudo-closed systems are those that exchange only a little energy but no matter with their surroundings. Throughput describes the energy and matter that flow into, through, and out of a system. A positive feedback isi a self-perpetuating process. In a positive feedback mechanism, increases in a state variable lead to further increases in that state variable. A negative feedback is a process that suppresses change and tends to maintain stability in a system. Homeostasis is a tendency to remain more or less stable and unchanging. Equilibrium is another term for stability in a system. Dynamic equilibrium is a tendency for a system to change and then return to normal. Disturbances are events that can destabilize or change the system. Resilience is the ability to recover from disturbance. Sometimes severe disturbance can lead to a state shift, in which conditions do not return to “normal”. Emergent properties are characteristics of the system that are greater than the sum of its parts.
—February 2021
Lance Jones 