Trophic level

The word “trophic” is Greek, and is a term used to describe the flow of energy through a given ecosystem. In most ecosystems there are four trophic levels. The first is occupied by the primary producers, photosynthetic plants that convert a small portion of the incoming solar energy into edible biomass. The second is occupied by primary consumers that feed on plants. The third is occupied by the secondary consumers, and they feed on primary consumers, either by predation or scavenging dead animal carcasses. The final level, level four, is occupied by the top carnivores, and these predators feed on secondary and primary consumer groups, while some even feed on primary producers (e.g., the grizzly bear is mostly a herbivore, but you couldn’t tell that by looking at one!). The efficiency of the system is at about 10%. That is how much of the available energy is converted to biomass of the next trophic level. The rest, 90%, is dissipated as heat due to metabolism and respiration.

Links
  http://www.csuchico.edu/~pmaslin/limno/trophic.html