Climate | Energy | Land | Water | Algae/Fungi | Epiphytes | Fauna | Fish | Water Plants | Nutrient Cycles | Social
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Project Amazonia: Characterization -
Energy Flow
From the solar energy that gets to the Earth, a very small fraction (approximately 0.1% worldwide) is derived to living systems. Even if the light falls on a zone with abundant vegetation, like a rainforest, only between 1 and 3% of that light (calculated on an annual basis) is used in photosynthesis, thus becoming available for the organisms that form part of that ecosystem. However, a very small fraction like this is enough to result in the production -from carbon dioxide, water, and a few minerals- of several million grams (in dry weight) of organic matter per square meter per year. This adds up to a worldwide total of approximately 120 thousand million metric tons of organic matter per year1. All the biotic and abiotic components of an ecosystem maintain the open exchange of matter and energy on which the system is based. The energy flow in an ecosystem is the most important factor in its organization. Several attributes inherent to an ecosystem are based on the matter and energy exchange:
As we can see, the movement of energy is open and in only one direction. This means that the energy goes through each trophic level one time. As it goes from one level to another, it is lost with metabolism and in the form of heat. This means that, for example, the energy ingested by producers does not pass completely to consumers. After the energy is lost as heat, it cannot be used for work anymore. The following equation makes this easy to understand. Pn = Pg – R Where2: · Net Primary Productivity (Pn) is a measure of the rate at which energy is fixed in the organisms’ biological tissues. This is the amount of energy that then passes to the following trophic level of the ecosystem. Thus, it can be considered as the amount of energy that is available to the ecosystem. It can also be thought of as the rate at which new biomass is being made by the plants. Generally, it is expressed as the amount of energy (in calories) stored in chemical compounds or as the increase in biomass (in grams or metric tons). · Gross Primary Productivity (Pg) is the photosynthetic rate or the rate at which energy is being fixed by photosynthetic organisms and stored in simple sugars.
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Respiration (R)
is the sum of all the organisms' metabolic costs. It represents a loss of energy
along the chain. 1: BIOLOGY 5th edition 1994, Worth Publishers Inc., New York 2: Lang, Ken <http://sorrel.humboldt.edu/~kll1/ecology.html>, 2002
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