Community Research and Development Information Service - CORDIS

Review of theoretical community ecology: implications for marine communities

If an ecosystem approach to fisheries management (EAFM) is to successfully address biodiversity issues then the mechanisms relating diversity and fishing activity need to be clearly understood, this in turn requires that processes that structure marine communities must be similarly understood. Community ecology has been the subject of much research, but mostly directed at terrestrial rather than marine systems. This material is reviewed to establish how much of it is relevant to marine communities.

The patterns in terrestrial community structure and the processes (eg competition, predation, disturbance, top-down, bottom up control) that give rise to such patterns are reviewed and examples from marine communities are then examined. Some of the 44 differences recorded between marine and terrestrial communities are profound and suggest that the theory explaining variation in structure of terrestrial communities may be irrelevant when applied to marine systems.

One particular difference relates to growth patterns, being characterised by deterministic growth in terrestrial species, suggesting that species are the ecological functional units allowing species diversity to be a useful concept with respect to such communities. However, marine species tend to be characterised by non-deterministic growth, resulting in considerable variation in niche use between different sized individuals of the same species. As a result it makes more sense to consider size classes of organisms as the basic ecological functional unit, rather than species. Thus, studies of the species diversity of marine communities must take account of the size structure of the organisms concerned.

Marine organisms tend not to display Lokta-Voltera type population dynamics, common in terrestrial organisms where annual per capita birth rates are constant, but show fecundity proportional to body mass, which continues to increase in non-deterministic growth, and consequently per capita fecundity also increases. As a consequence, the continuing increase in body mass of the individuals remaining after mortality has reduced their abundance, may maintain or even increase the potential for population growth. Furthermore, annual recruitment survival varies considerably between years, such that large cohorts can arise from low levels of reproductive stock.

Such population dynamics do not suit models such as DEM, and an alternative size-structured, species-interactive model is proposed which could provide the basis for predicting the effects of fishing on marine fish and benthic invertebrate species diversity.

Reported by

School of the Environment and Society
Singleton park
SA2 8PP SWANSEA
United Kingdom
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