Data Requirements and Community Assembly Rules

Network environ analysis could be referred to as a holistic/reductionistic approach. It is holistic because it considers simultaneously the whole influence of all system objects, yet it is reductionistic in that the fine details of all object transactions are entailed in the analysis. In other words, it is the opposite of a black box model. The network data requirements are considerable, which include the complete flow-storage quantities for each identified link and node (note flow and storage are interchangeable as determined by the turnover rate). Data can be acquired from empirical observations, literature estimates, model simulation results, or balancing procedures, when all but a few are unknown. This difficulty in obtaining data has resulted in a dearth of available complete network data sets. Due to this lack of requisite data for fully quantified food webs, researchers have developed community assembly rules that are heuristics to construct ecological food webs. Assembly rules are in general a set of rules that will generate a connectance matrix for a number of species (N). Common assembly rules that have been developed are random or constant connectance, cascade, niche, modified niche, and cyber-ecosystem, each with its own assumptions and limitations. In all but the last case, the assembly rules construct only the structural food web topology. The cyber-ecosystem methodology also includes a procedure for quantifying the flows along each link. It uses a metastructure of six functional groups: producer (P), herbivore (H), carnivore (C), omnivore (O), detritus (D), and detrital feeders (F), within which random connections link species based on these definitional constraints. Flows are assigned based on realistic thermodynamic constraints.

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