What is trophic energy?

Question

What is trophic energy?

Answer 1

Energy that is necessary for each level of the ecosystem.

Energy economy

An arctic food web. Each arrow represents a step-up in trophic level.

An arctic food web. Each arrow represents a step-up in trophic level.

Ecologists study the "energy economies" of natural systems. Foundation species (also known as primary producers) harvest an energy source such as sunlight and turn it into biomass. This biomass is consumed by other organisms (primary consumers), which are in turn consumed by others. Each link in this "chain" of consumption is termed a trophic level. Because only a fraction of the energy used by organisms at each trophic level is converted to biomass, less energy is available at higher levels.

Most ecosystems ultimately rely upon the Sun for energy and upon photosynthetic organisms to harness that energy. There are a few exceptions to this. For example, in deep sea hydrothermal vents and acid mine drainage, chemosynthetic archaea derive energy from the break down of sulfur rich compounds.

In terrestrial ecosystems, plants such as grass are the primary producers and form the first trophic level. Next are herbivores (primary consumers) that eat the grass, such as rabbits. Next are carnivores (secondary consumers) that eat the rabbits, such as a bobcats.

Keep in mind that trophic relationships are rarely this simple. Very often they are more of a "web" than a "chain." For example, mountain lions may eat both rabbits and bobcats. The trophic categorization of the mountain lion exists on two levels, possibly more.

Every time there is an exchange of energy between one trophic level and another, there is quite a significant loss due to the fundamental laws of thermodynamics. This means so many units of grass can only support a much smaller number of units of rabbits, who can only support a smaller group of bobcats, who can only support a smaller group of mountain lions. This is why trophic levels are usually portrayed as a pyramid, one that places grass on the bottom and mountain lions on top---the top is always much smaller than the bottom. Each level implies a loss of energy and efficiency and less life that can be supported by the sun.