| Popis: |
Herbivores constituted the highest trophic level in the models of the preceding chapters. Most food webs also contain carnivores that feed on the herbivores, and often second-order carnivores that feed on the first-order carnivores. In principle, chains with any number of trophic levels may exist within ecosystems. Empirical evidence, however, indicates that in nature the number of trophic levels within ecosystems seldom exceeds five or six. In an analysis of 56 ecosystems whose food webs have been characterized in detail, Pimm (1982) showed that the great majority (47) had three or four levels, while only five and two, respectively, had five and six trophic level chains. |
