dent and often overlap or partially fuse. 

 The relative importance of each submodel 

 within the ecosystem model is, of course, 

 variable among ecosystems. In aquatic and 

 wetland ecosystems this submodel interde- 

 pendency is epitomized (Hansen 1975), 

 and submodels of major ecosystems have 

 metamorphosed into integrated subsystem 

 models. 

 Modeling biological systems or attempting 

 biological simulation has evolved into the concep- 

 tualization of biological components and processes 

 against a background of physical and chemical 

 variables. Such models are often considered to 

 belong to one or more of the following hierarchical 

 classifications: 



1. Ecosystem models; 



2. Productivity models; 



3. Population models; and 



4. Process models. 



These are listed more or less in order of decreasing 

 complexity, but no hard and fast definitions are 

 possible. In our attempt to provide conceptual 

 modeling to a user package, the master models 

 (fig. 1) probably best demonstrate the ecosystem/ 

 process model approach while submodels are more 

 often population/process model oriented. 



The following display illustrates how we 

 expected the conceptual models to function in the 

 user package. Figure 2 is master model AE4 (fig. 1), 

 a simplified ecological/process model of an 

 estuarine intertidal system— emergent wetland with 

 salinity modifiers (i.e., salt and brackish marsh). 

 It is this model to which the user is first directed in 

 order to convey the physical, chemical, and biologi- 

 cal interactions and the primary driving forces. 

 This model is further dissected into component 

 system submodels: figure 3, AE41 (marsh); 

 figure 4, AE42 (water); and figure 5, AE43 (sedi- 

 ment). The user can refer to the appropriate sub- 

 model for specific information on master model 

 components. For example, if the user is interested 

 in evaluating the impact of dredge-and-fill opera- 

 tions in an estuarine emergent wetland, he is 

 directed by the master model to the marsh and 

 water submodel primary producer components. All 

 compartments in the submodels are numbered 

 (01-99) and specific organisms can be identified as 

 components by their associated alphanumeric code 

 (see submodels tor specific examples). Ecologically 

 and/or numerically important species could be 

 identified by this code in the characterization 

 narrative and atlas. 



CONCEPTUAL MODELING- 

 CURRENT APPROACH 



The interim procedure described above, while 

 attractive in theory, was extremely cumbersome to 

 use. The total number of master models and sub- 

 models needed for the entire study area would 

 have amounted to well over 100 and the technique 

 for referencing key species into the models would 

 have resulted in thousands of manhours for cita- 

 tion and annotation in the other characterization 

 products. In addition, the interim procedure did 

 little to communicate the contents of the charac- 

 terization products to primary users (i.e., field 

 biologists). 



The present approach attempts to provide a 

 user-oriented system of access to product informa- 

 tion as well as an ecological understanding of the 

 various habitats comprising the study area. The 

 modeling effort has been altered appreciably to 

 enhance the value of the models as primary com- 

 ponents of a "user package." The materials con- 

 tained in this "package" are assembled to supple- 

 ment and provide rational entry into the principal 

 products of the characterization project (i.e., nana- 

 tive, atlas, data appendix, and bibliography). The 

 package is a user guide and is composed of four 

 major parts: an executive summary, models, 

 habitat distribution of various species, and inter- 

 action matrices. The executive summary' will pro- 

 vide an introduction to characterization concepts, 

 a brief summary of the sea island ecosystems and 

 general instructions for using the package 

 components for data search and retrieval. Models 

 are included to acquaint the reader with the princi- 

 pal components of each ecosystem and the extrin- 

 sic forces and intrinsic relationships associated with 

 these components. The models are presented in a 

 diagrammatic (energese) and a pictorial mode, 

 hence combinatorial. The ecological sketches are 

 brief narratives on "high priority" species, and 

 summarize their reproductive and cover require- 

 ments, and impinging human activities. Finally, the 

 interaction matrices will form the central com- 

 ponent of the user package. Each ecosystem will be 

 supported by a single matrix which cross-references 

 common environmental alterations with existing 

 environmental characteristics. Each intersection of 

 the matrix will thus provide appropriate entry into 

 the characterization products. 



The functional components of the user package 

 are the combinatorial models, ecological sketches, 

 and the interaction matrices. The combinatorial 



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