Measurement of Scope for Change in Ascendency for Short-Term Assessment of Community Stress

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Abstract
Scope for growth, or the resource balance of an organism or population, has been used as a comparative descriptor for the short-term assessment of stress effects. This concept may be extended to all levels of biological organization, and in particular to the assessment of early responses of communities to anthropogenic stress (or subsidy). The size (throughput) and development (organization) of a biological system can be described by the state function ascendency. We define the scope for change in ascendency of a biological system as the difference between the ascendency of inputs and the ascendency of outputs. This balance increases when a resource subsidy is used by the system to build size and organization, and decreases under stress. Changes in a system's resource balance and distribution in terms of flows help trace effects at one level to effects at the other. Computer simulations of an epilimnion community indicated that scope for change in ascendency gives a sensitive and fast response to perturbations. This index may provide a means for short-term assessment of anthropogenic stress, or management options.

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