How does the flow of energy through living systems help determine the components of a biological community?

Question

How does the flow of energy through living systems help determine the components of a biological community?

Answer 1

Trophic dynamics studies the flow of of energy and nutrient transfer between organisms. Two of the most significant theories of the field relate to your question. One is the "bottom up" control on the energy structure of ecosystems by determining the total amount of energy that enters the system. As one moves up to higher trophic levels (i.e. from plants to top-carnivores) the total amount of energy decreases. Primary energy gathering is performed at the bottom rung of the trophic ladder and so there is a "bottom up" control on populations at higher trophic levels.

There is also a "top down" effect. The effect known as a trophic cascade occurs when predators in a food chain suppress the abundance of their prey, thereby releasing the next lower trophic level from predation.

These various energy balances are one of the primary influences controlling the populations of various members of the biological community.

The other primary primary influence is the availability of various nutrients and water. Typically there is one limiting nutrient that in combination with limited energy and limited water together determine both the makeup (types of organisms) and various average populations of the ecosystem.

Answer 2

Energy comes in many forms.  The most common and simplest energy flow model is based on the capture of sunlight energy by primary producers (e.g., algae or grass).  The energy passes up a food chain to consumers (algae-eating insect larvae or cows at trophic level 1), then further up the food chain to predatory consumers (fish or humans).  In this simplistic model, the transfer of energy up the food chain results in smaller amounts of biomass being present at each successively higher trophic level.  This means the that the bio-community will have as components lots of primary producers, fewer consumers, and even fewer predators at the higher trophic levels.

But here is another example of energy "flowing through" a living system.  Consider the community that lives in the rocky intertidal zone - there are barnacles, mussels, snails, and perhaps starfish.  While some primary production goes on in this system, there's another BIG energy flow at work - the rising and falling of the tides and the constant energy input from the waves.  This is not sunlight energy, but kinetic energy that moves water around.  The organisms of the biological community take advantage of this.  Much of the biological community consists of detritivores and filter feeders.   They are attached to rocks and they depend on the kinetic energy in the system to constantly bring them water with a fresh supply of detritus and algae.  From the standpoint of energetics, the rocky intertidal zone bio-communiy's structure is dependent on organic matter imported from other nearby biological communities.