A generalized model of energy flow (Heal and Maclean, 1975) provides a complete description file trophic structure of a community (Fig. 4.5a).
Besides the grazer system pyramid of productivity, t kits two additional elements.
A decomposer system and subcomponents of each trophic level, a distinction is made between vertebrate and invertebrate types, between detritivores and microbes which belong to the same trophic level and utilize dead organic matter, and also between consumers of microbes (microbivores) and of detritivores.
However, patterns of energy flow differ in different communities when we compare the patterns of energy flow in a forest, a grassland, a small stream, a large lake or ocean, we find interesting differences not only in their net primary production but also in their grazer system (Fig. 4.5b). In every community, the decomposer system is responsible for the major part of secondary production and therefore heat loss in respiration.
The grazer system has its greatest role in plankton community of a large lake or of the ocean, where a large part of net primary production is consumed alive and assimilated at a high efficiency. However, the grazer system has little influence in terrestrial communities because of low herbivore consumption and assimilation, and it has very little or no role in small streams and ponds as their primary production is quite low.
Streams and ponds depend for their energy on dead community. In the deep ocean also the community derives its energy base from dead phytoplankton, bacteria, animals and faecal matter which come from the autotrophic component in the euphotic zone.