The systems of nature that depend largely or entirely on the direct rays of the sun can be designated as unsubsidized solar – powered ecosystems. They are unsubsidized in the sense there is little, if any, available auxiliary source of energy to enhance or supplement solar radiation. The open oceans, large tracts of upland forests and grasslands, and large deep lakes are examples of relatively unsubsidized solar – powered ecosystems. Frequently, they are subjected to other limitations as well, as, for example, a shortage of nut re = ients or water. Consequently, ecosystems in this broad category vary widely, but are generally low powered and have a low productivity, or capacity to do work. Organisms that populate such systems have evolved remarkable adaptations for living on, and efficiently using, scarce energy and other resources.
Major sources of energy Ecosystem

     Although the ‘’power density’’ of natural ecosystem in this first category is not very impressive, nor could such ecosystems by themselves support a high density of people, they are none the less extremely important because of their huge extent (the oceans alone cover almost 70% of the globe). From the human interest standpoint the aggregate of solar – powered, natural ecosystem can be thought of, and the certainly should be highly valued, as the basic life – support module which provide desirable stability and homeostatic control for spaceship earth. It is here that large volumes of air are purified daily, water recycled, climates controlled, weather moderated, and much other useful work accomplished. A portion of man’s  food and fiber needs are also produced as a by – product without economic cost or management effort by man. This evaluation, of course, does not include the priclude the priceless aesthetic values inherent in a sweeping view of the ocean, or the grandeur of an unman aged forest, or the cultural desirability of green open space.

      Where auxiliary sources of energy can be utilized to augment solar radiation the power density can be considerably, perhaps an order of magnitude. In this frame of reference an energy subsidy is an auxiliary energy source that reduces the unit cost of self – maintenance of the ecosystem, and thereby increases the amount of solar energy that can be converted to organic production. In other words, solar energy is augmented by non solar energy freeing it for organic production. Such subsidies can be either natural or man – made (or, of course, both). For the purpose of our simplified classification we have listed naturally subsidized and man – subsidized solar – powered ecosystems.
ecosystems energy example

       A coastal estuary is a good example of a natural ecosystem subsidized by the energy of tides, waves, and currents. Since the back and forth flow of water does prt of the necessary work of recycling mineral nutrients and transporting food and wastes, the organisms in an estuary are able to concentrate their efforts, so to speak , on more efficient conversion of sun energy to organic matter. In a very real sense, organisms in the estuary are adapted to utilize tidal power. Consequently, estuaries tend to be more fertile than, say, an adjacent land area or pond which receives the same solar input, but does not have the benefit of the tidal and other water flow energy subsidy. Subsidies that enhance productivity can take many other forms, as for example, wind and rain in a tropical rain forest, the flowing water of a stream, or imported organic matter and nutrients received by a small lake from it watershed.

        Man, of course, learned early how to modify and subsidize nature for his direct benefit, and he has become increasingly skillful in not only productivity, but more especially in channeling that productivity into food and fiber materials that are easily harvested, processed, and used. Agriculture (land culture) and aquaculture (water culture) are the man subsidized solar – power ecosystems. High yields of food are maintained by large inputs of fuel (and in more primitive agriculture, human and animal labor) involved in cultivation, irrigation, fertilization, genetic selection, and pest control. Thus, tractor fuel, as will as animal or human labor, is just as much an energy input in aggro – ecosystems as sunlight, and it can be measured as calories or horsepower expended,not only in the field, but also in processing and transporting food to the supermarket. As H. T. Odom (1971) was so aptly expressed it, the bread, rice, orn, and potatoes which feed the masses of people are partly made of oil. This is why fuel, or some comparable auxiliary energy, is vital to food production for man.

        It is very important to note that recent increases in crop yield, the so – called ‘’green revolution,’’ has resulted from genetic selection of plants, not so much for their ability to utilize solar energy as for their ability to benefit from fuel subsidies. Thus, what has been called in the popular press ‘’miracle’’ rice and wheat are dwarf plants with small root systems and just enough leaves and stem to capture a maximum of usable solar radiation. Since man’s fuel and chemicals do most of the work of protection and maintenance that a wild plant would have to do with an expenditure of its own energies, the crop plant is able to convert more of the sun energy into grain. It can do this because it is highly selected (that is, genetically programmed) to produce grain at the expense of non edible tissue. Pouring the fertilizer, or other subsidies, on a wild rice plant would not have such a great effect on grain yield since the wild plant would be programmed to use the additional resources for stalks and leaves as well as grain. Man’s skill in augmenting the natural conversion of sun energy into food in this fashion parallels nature’s own design and has, at least temporarily, staved off starvation in some parts of the world. However, the fuel subsidized ogre – ecosystem is not without its economic and pollution costs resulting from the heavy energy consumption the he high degree of genetic specialization produces an inherent vulnerability to disease. Whether fuel subsidized food production and rising per capita.