EMECO

Higher Trophic Level Models

Higher trophic level models represent the biological components of the system. Most, if not all, are fundamentally based on feeding relationships or “trophic interactions”. To represent the trophic interaction of a marine system, all living components must be included. However, representing every species requires an enormous amount of information, most of which is not available, particularly at lower trophic levels. Therefore, higher trophic level models tend to be more resolved at the top of the food chain and highly aggregated at the based of the food chain. Many higher trophic level models are constructed for fisheries research, more specifically, to model the ecological interactions of commercial fish species. Size-based models and Ecopath with Ecosim are common higher trophic level models.

Size-based Models

Size based or size structured models represent the biological ecosystem component. They are constructed on the general principle that larger organisms eat smaller organisms. There are many size based models that have been constructed. They can be used as stand alone models to investigate the complex trophic interaction that occur within the biological part of the system, or they can be coupled with biogeochemical models, such as BFM to study the interaction between the chemical and biological components. They can also be used to research the likely impacts of increased or decreased fishing effort on the ecosystem structure and function.

Ecopath with Ecosim

Ecopath with Ecosim is a mass balance trophic model, which is based on the assumption that what enters the system (via immigration and birth rates) is equal to what leaves the system (via mortality and emigration). Like size based models, EwE models can be used as stand alone models that represent the interactions within the biological ecosystem component, coupled with biogeochemical models to study the interaction between the chemical and biological components, and used to simulate the effect of changes in fishing effort.