Ecosystems
The three main distinguishing characteristics of an ecosystem are:
 Energy Flow
 Nutrient Cycling
 Population Self-Regulation
An ecosystem is stable when these three variables are interacting in a state of balance or
equilibrium. The way to understand the interrelationships in an ecosystem is to analyze the flow
of energy. Radiant energy from the sun is the ultimate source of energy for the majority of
processes on the planet. The sun’s radiant energy is trapped by plants through photosynthesis.
Even the energy in coal, oil, and natural gas reserves was originally trapped by photosynthesis.
Only a small part of the sun’s energy that reaches the earth is actually trapped by plants.
At each stage of energy transfer, some of the energy is lost as heat, so that the amount of energy
available for work keeps decreasing. If the energy from the sun were diminished or cut off, the
quantity of life energy on the earth would correspondingly diminish or cease. A constant influx
of energy from the sun is needed to keep the earth’s systems going.
Nutrients in an ecosystem move through a four-stage cycle. These stages are: nutrient
pool, producers, consumers, and decomposers. The nutrient pool is the earth itself, consisting of
oxygen, carbon dioxide, water, soil, rocks, minerals, etc. Producers are the green algae and
various plants that combine nutrients, using the energy from the sun, into complex molecules
called carbohydrates that are the simple building blocks of life. Producers change radiant energy
into chemical energy. Consumers are organisms of three types that get their energy and material
substance from producers either directly or indirectly. The three types of consumers are:
herbivores, carnivores, and omnivores. Decomposers are organisms like bacteria, fungi, worms
and beetles that break down dead plant and animal matter so that the elements of which it was
composed can be made available for use again in the nutrient pool.
Decomposers are a vital link in the natural recycling process and are often the missing
link in systems set by humans. Basically, decomposition consists of releasing enzymes into dead
plans and animals, causing their bodies to be digested. The decomposers then absorb this matter
through their normal metabolic processes to release basic elements for reuse by producers.
When a population is balanced, there is a relationship between predator, prey, and
nutrient supply such that one species does not expand so greatly that the ecosystem is thrown out
of balance. There are many examples of unbalanced systems and often the imbalance is due to
man’s intervention.