118 LEFFLER 



characterize the ecosystem, and the history of the system. Each 

 factor must be rigorously specified before predictions about an 

 ecosystem's stress response can be made. This recognition greatly 

 limits our ability to generalize about the perturbed behavior of 

 ecological systems. Data from microcosm studies were used to 

 illustrate the possible effects of these three factors. Empirical 

 evaluation of hypotheses concerning an ecosystem's response to 

 stress is sorely needed. The rigorous design and specificity of 

 analysis required limit generalization of results but may enhance 

 understanding of ecosystem dynamics when used in conjunction with 

 mathematical and intuitive methods. 



ACKNOWLEDGMENTS 



I thank G. T. Auble, M. C. Chase, F. B. Golley, J. V. Nabholz, 

 and C. L. Thomas for their critical comments on earlier drafts of this 

 paper. Microcosm research was supported by grant BMS-75-19765 

 from the National Science Foundation. 



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