Biosphere Contents

4. Interdependence

The inter-relationships within a food web can be summarised by placing species within different trophic levels, depending on what they eat

The idea of levels in a food web was first put forward in a posthumous paper by the American Raymond Lindemann in 1942. He suggested that producers form level one, herbivores level two, carnivores level three and 'top carnivores' level four. More than four trophic levels are rarely present. When communities are divided into trophic levels they also form a pyramid, at first glance rather like Elton's, with most of the biomass usually found among the primary producers. The Lindemann model is a simplification however, because some species feed at more than one trophic level. These are referred to in the ecological literature as omnivores. A second problem with a trophic level approach to communities is that it ignores decomposers, although these are sometimes added to the base of the pyramid.

Trophic pyramid

What does Lindeman's model represent?