STRESS AND ECOSYSTEMS 



ARIEL E. LUGO* 



Department of Botany and Center for Wetlands, University of Florida, 



Gainesville, Florida 



ABSTRACT 



The literature dealing with issues of stress as it affects ecosystems is reviewed. 

 Definitions of stress are discussed. Models and literature examples are presented 

 to illustrate the push — pull (positive — negative) effects of most stressors and to 

 suggest that the point of attack and the type of stressor determine the rate of 

 response of the ecosystem. Stressors with high-quality energies (highly concen- 

 trated energy sources) that divert low-quality energy flows in a system appear to 

 have a greater impact than stressors with low-quality energy (diluted energy 

 sources) that impact high-quality energy flows. It is suggested that ecosystem 

 complexity (including species diversity, physiognomy, three dimensional organi- 

 zation, etc.) is a function of the balance between energies that contribute to 

 growth and organization and those that contribute to disorder. The classification 

 of environments by their "energy signatures" (the sum of all incoming energy 

 flows into a system and the pattern of their delivery expressed on equal 

 energy-quality basis) is presented as the best way to arrange and analyze 

 ecosystems hierarchically according to their capacity to develop complexity and 

 to tolerate stress. The patterns of ecosystem response to stressors, including 

 positive, steady-state, and declining responses and possible extinction, are 

 discussed. It is argued that, to solve the problems of ecosystem management and 

 the issues of environmental impact, studies and analyses must be done at the 

 level of the ecosystem and care should be taken to quantify both the stressor 

 and the stress with units of comparable energy quality. 



Today most of the biosphere has been altered in some way by the 

 activities of man. With human impact on ecosystems becoming more 

 obvious and more damaging to the economy of nations, the 

 ecologist's interests are changing from descriptions of steady-state 

 ecosystems to studies of ecosystem perturbations and their imphca- 



*Current address: Council on Environmental Quality, Washington, D. C. 



62 



