Community Research and Development Information Service - CORDIS

Provision of the ecological based model

It was hoped that Huston's (1994) Dynamic Equilibrium Model (DEM) which is based on the relationship between disturbance, diversity and productivity, might be used as an algorithm to assess the impacts on diversity (a requirement of many environmental directives) as a result of disturbance (from fishing activity) in areas of differing productivity within the North Sea.

However, three explicit tests of the DEM were carried out and in each the data failed to support hypotheses derived from the DEM and it therefore proved to be inappropriate for the task of providing scientific advice in support of an EAFM attempting to meet biodiversity objectives for the north Sea. The reason for this failure is likely to be that the DEM assumes Lokta-Voltera type population dynamics, whereby population growth is directly proportional to the abundance of mature individuals within the population. For many marine fish and benthic species this is an inappropriate assumption because of the "storage" and "lottery" dynamics of their reproductive output, associated with their non- deterministic growth and the stochastic nature of their recruitment.

The DEM also describes the diversity of the species as a function of variation in productivity and disturbance, but where non-deterministic growth is occurring within populations it is preferable to use body size as the functional unit rather than the species. As a consequence, a size structured species diversity model has been outlined and developed, and the analyses carried out to date suggest that such a model may provide useful insight for scientists advising an EAFM addressing biodiversity issues.

Reported by

Swansea University
Singleton park
United Kingdom
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