PREFACE V 



of the other components or of the overall system may 

 be positive. For instance, species diversity or equita- 

 bility may increase during periods of stressful environ- 

 mental fluctuations if the average compensatory effi- 

 ciency of the community members is superior to that of 

 a species which is normally dominant in less-extreme or 

 more-constant conditions. 



Operational definitions of stress or strain frequently 

 reflected the subdisciplines and areas of interest of the 

 investigators. For example, Lugo, w^ho classified envi- 

 ronments by their "energy signatures," defined stress in 

 terms of a drain of potential energy from a system; 

 whereas Esch and Hazen described the homeostatic 

 stress response of largemouth bass to thermal effluents 

 and bacterial infection. Ulanovdcz, however, was con- 

 cerned with linear and nonlinear modeling of inputs and 

 the resultant strain, in a mechanistic sense, imposed on 

 the ecosystem. We will not provide here an additional 

 definition of stress, but we caution the readers to 

 consider the operational definitions carefully before 

 comparing individual studies. 



The first section of this volume is devoted to 

 modeling stress, because ultimately the ability to model 

 and, thus, predict the stress response is a primary raison 

 d'etre for funding stress research. In his review paper on 

 modeling stress, Ulanowicz classifies existing models 

 according to whether they track local or far-field stress. 

 He also discusses the success of various attempts at 

 linear and nonlinear modeling of the effects on ecosys- 

 tem properties of endogenous and exogenous stressors. 

 Dv^er et al., however, contend that an "adequate 

 description of ecosystem stability properties cannot 

 always be derived from a linearized model of the 

 ecosystem." They used techniques of spectral analysis 

 to analyze phytoplankton abundance in a system 

 exposed to time-varying inputs. 



Accurate prediction of a system's response to 

 anthropogenic stressors frequently requires an under- 

 standing of the nature of a system's response to natural 

 perturbations. In his review of studies of stressed 

 ecosystems, Lugo proposes that the energetic quality of 

 both the stressor and the receiving system determines the 

 severity of response to a perturbation. He also maintains 

 that the stability of an ecosystem depends on the 



