range of laboratory test conditions is narrower than the range of natural 

 conditions and when forcing functions and rate coefficients are derived singly 

 but applied synergistically. It should also be pointed out that when empirical 

 and mechanistic models are connected to represent complex ecological processes 

 and interactions the predictive capability of the integrated/linked models 

 rapidly diminishes. 



III. CONSIDERATION OF HOLISTIC AND LIMITED COMPONENTS ECOSYSTEM MODELS 

 Holistic Ecosystem Models 



The development of generic holistic ecosystem models that apply to many 

 environmental problems and habitats does not appear to be practical or prudent. 

 The detailed structures of a model depend strongly on the problem being addressed 

 and the habitat of concern. A model with a versatile structure for widespread 

 problematic, geographic, and habitat application would be impossibly complex. 

 For instance, to model problems that are dominated by physical transport 

 processes (e.g., oil spill trajectories), detailed representations of hydrodynamic 

 processes would be required. Nutrient enrichment problems would need detailed 

 descriptions of bacterial and planktonic communities in addition to the 

 hydrodynamics. The movement of toxic substances through biotic networks requires 

 detailed descriptions of macrophyte, invertebrate, and vertebrate communities 

 and interactions. A model designed to treat spills, eutrophication, and 

 bioaccumulation of toxics in even one limited geographical area would require 

 field and laboratory studies several orders of magnitude more costly than is 

 warranted by the economics of the problem(s) being addressed. Hence, it would 

 not be cost effective to attempt to develop even a single-site holistic model 

 let alone a site-adaptable and problem-adaptable generic model. 



Limited Components Ecosystem Models 



Most resource management problems can be addressed more cost effectively 

 by considering only that portion (structure and function defined in time and 

 space) of an ecosystem which is directly involved in the management problem/con- 

 cern/question. For example, until an oil spill contacts a species of interest, 

 transport concerns dominate the problem. Once the species has been contacted, 

 biological concerns dominate. In this case, transport and single-species models 

 would be far more appropriate than a comprehensive ecosystem model. For fisheries 

 problems where factors such as temperature, food, weather events, and the 

 locomotive ability of the species dominate over physical transport processes, a 

 population or trophic dynamics model would be adequate to meet the management 

 concerns . 



IV. PLANNING AND DESIGN OF ECOSYSTEM ANALYSIS AND ASSESSMENT PROGRAMS 



Definition and Execution of Program Objectives 



If it is to be effective, an ecosystem analysis and assessment program 

 needs a clearly stated objective and plan of execution. One of the early steps 

 in the development of the program is to recognize and formulate an acceptable 

 trade-off between what information the manager would like to have to make an 

 "absolutely perfect" decision and what information can be generated within the 



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