Embedded Files
Ecosystems maintain themselves by transferring energy and cycling nutrients obtained from external sources. At the first trophic level, producers (plants, algae, and some bacteria) use solar energy to produce energy-rich organic compounds (glucose and other carbohydrates) through photosynthesis. We can represent the energy and nutrient flow through an ecosystem as a food chain or a food web.
Herbivores—animals that feed solely on plants—make up the secondtrophic level. Carnivores that eat herbivores comprise the third trophic level.There are two different kinds of carnivores: predators and scavengers.
On average only about 10 percent of the energy at one trophic level is passed on to the next level. That means that 90% of the energy available to a trophic level is used up and lost as heat as the consumer converts those calories to ATP and puts that energy to use. Processes that reduce the energy transferred between trophic levels include respiration, growth, excretion and reproduction; in other words, the organisms' metabolisms. Since all of the energy that was originally absorbed from the sun is used up,the presence of autotrophs is absolutely necessary for the stability of the food chain.
This partial transfer of energy is represented by a pyramid where the producers (aka autotrophs) are at the bottom, and the predators and/or scavengers are on the top. The pyramid represents both the amount of energy contained in the organisms at each level as well as the sizes of the populations at each level.
Nutrients, however, cannot be used up and lost. It is a fundamental law of the universe, actually. Matter can neither be created or destroyed. It can only change form. When organic matter is no longer part of a living organism, its complex molecules must be broken down into very simple ones so that autotrophs can absorb them (basically as fertilizer) and put them back into the food chain. The most important nutrient that plants need is nitrogen, but others such as phosphorous and sulfur are also necessary.
The vital organisms in an ecosystem that have the ability to break down complex organic material around them are called decomposers. These important organisms are also called saprophytes or saprobes. They do not eat and digest inside their bodies like we do. They secrete their digestive enzymes out into their surroundings which causes the proteins, lipids, and complex carbs from dead organisms (or living organisms' wastes) to break down into very basic compounds such as nitrates and ammonia. These basic molecules then serve as nutrients for producers, who absorb them from the soil along with water. The decomposers don't do this selflessly of course. They absorb much of the broken down nutrients for themselves as well.
Report abuse