Other factors that can lead to a decrease in Primary production can be water. A decrease in any of these factors can cause a decrease in the level of Primary Production. The process of primary production must take place as it is the base or foundation of the food chain. Therefore if due to any reason it gets disturbed, the entire food chain will be shaken.
Both of them are different in terms of dependency on chlorophyll and terms of consumer and producer. NPP stands for net primary production. For example, look at the range of production values Y axis at a temperature value of 10 deg C or at a precipitation value of mm. The scatter or variation in the production due in part to other aspects of particular local systems, such as their nutrient availability or their turnover rates.
For example, grasslands can have a relatively high rate of primary production occurring during a brief growing season, yet the standing crop biomass is never very great. This is indicative of a high turnover rate.
In a forest, on the other hand, the standing crop biomass of above-ground wood and below-ground roots is large.
Each year's production of new plant matter is a small fraction of total standing crop, and so the turnover of forest biomass is much lower.
Another good example is seen in the oceans, where most of the primary production is concentrated in microscopic algae. Algae have short life cycles, multiply rapidly, do not generate much biomass relative to their numbers, and are eaten rapidly by herbivores. At any given point in time, then, the standing crop of algae in an ocean is likely low, but the turnover rate can be high see below We have now examined the first step in the flow of energy through ecosystems: the conversion of energy by primary producers into a form that is usable by heterotrophs, as well as by producers themselves.
In the next lecture we will examine how this energy moves through the rest of the ecosystem, providing fuel for life at higher trophic levels. Summary of Part 1, Primary Production Organisms are characterized as autotrophs and heterotrophs. Autotrophs produce their own food by fixing energy through photosynthesis or, less commonly, chemosynthesis. Heterotrophs must feed on other organisms to obtain energy.
Primary production is the creation of new organic matter by plants and other autotrophs. It can be described per unit area for individual ecosystems or worldwide. Production also is a rate, measured per time unit, while standing crop biomass is the amount of plant matter at a given point in time.
The ratio of standing crop to production is called turnover. The turnover time of a system is important in determining how a system functions. Production rates can be quantified by a simple method by which oxygen or carbon production is measured. Production can also be quantified by measuring the rate of new biomass accumulation over time. The distinction between gross primary production GPP , net primary production NPP , and net ecosystem production NEP is critical for understanding the energy balance in plants and in whole ecosystems.
Production varies among ecosystems, as well as over time within ecosystems. Rates of production are determined by such factors as climate and nutrient supply. Precipitation is the dominant control worldwide, but nutrient availability often limits primary production in any particular, local system.
The Flow of Energy to Higher Trophic Levels In the section above we examined the creation of organic matter by primary producers. Without autotrophs, there would be no energy available to all other organisms that lack the capability of fixing light energy.
However, the continual loss of energy due to metabolic activity puts limits on how much energy is available to higher trophic levels this is explained by the Second Law of Thermodynamics.
Today we will look at how and where this energy moves through an ecosystem once it is incorporated into organic matter. Most of you are now familiar with the concept of the trophic level see Figure 1.
It is simply a feeding level, as often represented in a food chain or food web. Primary producers comprise the bottom trophic level, followed by primary consumers herbivores , then secondary consumers carnivores feeding on herbivores , and so on.
When we talk of moving "up" the food chain, we are speaking figuratively and mean that we move from plants to herbivores to carnivores. This does not take into account decomposers and detritivores organisms that feed on dead organic matter , which make up their own, highly important trophic pathways.
Figure 1: Trophic levels. What happens to the NPP that is produced and then stored as plant biomass at the lowest trophic level? On average, it is consumed or decomposed. If NPP was not consumed, it would pile up somewhere. Usually this doesn't happen, but during periods of Earth's history such as the Carboniferous and Pennsylvanian, enormous amounts of NPP in excess of the degradation of organic matter accumulated in swamps. It was buried and compressed to form the coal and oil deposits that we mine today.
When we burn these deposits same chemical reaction as above except that there is greater energy produced we release the energy to drive the machines of industry, and of course the CO 2 goes into the atmosphere as a greenhouse gas. This is the situation that we have today, where the excess CO 2 from burning these deposits past excess NPP is going into the atmosphere and building up over time, dramatically changing our climate.
But let's get back to an ecosystem that is balanced, or in "steady state" "equilibrium" where annual total respiration balances annual total GPP. As energy passes from trophic level to trophic level, the following rules apply: Only a fraction of the energy available at one trophic level is transferred to the next trophic level.
Typically the numbers and biomass of organisms decrease as one ascends the food chain. An Example: The Fox and the Hare To understand these rules, we must examine what happens to energy within a food chain. Suppose we have some amount of plant matter consumed by hares, and the hares are in turn consumed by foxes.
The following diagram Figure 2 illustrates how this works in terms of the energy losses at each level. A hare or a population of hares ingests plant matter; we'll call this ingestion. Part of this material is processed by the digestive system and used to make new cells or tissues, and this part is called assimilation.
What cannot be assimilated, for example maybe some parts of the plant stems or roots, exits the hare's body and this is called excretion. The hare uses a significant fraction of the assimilated energy just being a hare -- maintaining a high, constant body temperature, synthesizing proteins, and hopping about. This energy used lost is attributed to cellular respiration.
The remainder goes into making more hare biomass by growth and reproduction that is, increasing the overall biomass of hares by creating offspring. The conversion of assimilated energy into new tissue is termed secondary production in consumers, and it is conceptually the same as the primary production or NPP of plants.
In our example, the secondary production of the hare is the energy available to foxes who eat the hares for their needs.
Clearly, because of all of the energy costs of hares engaged in normal metabolic activities, the energy available to foxes is much less than the energy available to hares. Just as we calculated the assimilation efficiency above, we can also calculate the net production efficiency for any organism. This efficiency is equal to the production divided by the assimilation for animals, or the NPP divided by the GPP for plants.
The "production" here refers to growth plus reproduction. These ratios measure the efficiency with which an organism converts assimilated energy into primary or secondary production. These efficiencies vary among organisms, largely due to widely differing metabolic requirements. The reason that some organisms have such low net production efficiencies is that they are homeotherms , or animals that maintain a constant internal body temperature mammals and birds. This requires much more energy than is used by poikilotherms , which are also known as "cold-blooded" organisms all invertebrates, some vertebrates, and all plants, even though plants don't have "blood" that do not regulate their temperatures internally.
Just as we can build our understanding of a system from the individual to the population to the community, we can now examine whole trophic levels by calculating ecological efficiencies.
You might think of it as the efficiency of hares at converting plants into fox food. Note that the ecological efficiency is a "combined" measure that takes into account both the assimilation and net production efficiencies. You can also combine different species of plants and animals into a single trophic level, and then examine the ecological efficiency of for example all of the plants in a field being fed on my all of the different grazers from insects to cows.
Thinking about the overall ecological efficiency in a system brings us back to our first rule for the transfer of energy through trophic levels and up the food chain. For example, If hares consumed kcal of plant energy, they might only be able to form kcal of new hare tissue. For the hare population to be in steady state neither increasing nor decreasing , each year's consumption of hares by foxes should roughly equal each year's production of new hare biomass. So the foxes consume about kcal of hare biomass, and convert perhaps 10 kcal into new fox biomass.
The overall loss of energy from lower to higher trophic levels is important in setting the absolute number of trophic levels that any ecosystem can contain. From this understanding, it should be obvious that the mass of foxes should be less than the mass of hares, and the mass of hares less than the mass of plants. Generally this is true, and we can represent this concept visually by constructing a pyramid of biomass for any ecosystem see Figure 3.
A pyramid of biomass showing producers and consumers in a marine ecosystem. Pyramids of Biomass, Energy, and Numbers A pyramid of biomass is a representation of the amount of energy contained in biomass, at different trophic levels for a given point in time Figure 3, above, Figure 4-middle below.
The amount of energy available to one trophic level is limited by the amount stored by the level below. Because energy is lost in the transfer from one level to the next, there is successively less total energy as you move up trophic levels. In general, we would expect that higher trophic levels would have less total biomass than those below, because less energy is available to them.
Primary production, in short, is the study of plant growth in ecosystems that forms the base or primary factors in the food web and how they produce food for other organisms.
The term is also involved in ecological efficiency which describes the transfer of energy from a trophic level to the next. Ecological efficiency is based on factors that are related to resource acquisition and assimilation of organisms in the ecosystem. Primary production also covers the processing and production of organic components from the atmospheric or aquatic carbon dioxide. The processes of photosynthesis and chemosynthesis are also notable in primary production.
The main source of energy in the production of chemical energy in organic compounds comes from the sunlight, but a small portion of it comes from the inorganic molecules of lithotrophic organisms. This energy is converted, mainly by plants and algae, to synthesize complex organic molecules into simpler, organic compounds like water. Simple molecules can also be synthesized to make more complicated as well, like proteins, and can be respired to perform work.
To measure these factors, gross primary production and net primary production are used. Field, C. Primary production of the biosphere: Integrating terrestrial and oceanic components. Gough, C.
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