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.