Primary production is the study of organisms, mostly plants, and how they provide the supplements to other organisms.
They are called gross primary production and net primary production. Gross primary production is the rate at which the producers in an ecosystem capture and store a given amount of chemical energy as biomass in a given span of time while net primary production is the measurement rate of primary producers in an ecosystem to produce net useful chemical energy.
Primary production can be affected by the productivity of the ecosystem. Difference Between Similar Terms and Objects. MLA 8 J, Martin. Name required. Email required.
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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. It is defined as the rate at which every autotroph which is included in the ecosystem produces net chemical energy. It is the difference between the rate of total useful chemical energy produced and the rate at which some of its useful chemical energy is used for the respiration process. GPP stands for Gross primary production.
It is defined as the rate at which every autotroph which is included in the ecosystem produces useful chemical energy. 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. We could also construct a pyramid of numbers , which as its name implies represents the number of organisms in each trophic level see Figure 4-top.
For the grassland shown in Figure 4-top, the bottom level would be quite large, due to the enormous number of small plants grasses. For other ecosystems such as the temperate forest, the pyramid of numbers might be inverted: for instance, if a forest's plant community was composed of only a handful of very large trees, and yet there were many millions of insect grazers which ate the plant material. Just as with the inverted pyramid of numbers, in some rare exceptions, there could be an inverted pyramid of biomass, where the biomass of the lower trophic level is less than the biomass of the next higher trophic level.
The oceans are such an exception because at any point in time the total amount of biomass in microscopic algae is small. Thus a pyramid of biomass for the oceans can appear inverted see Figure 4b-middle.
You should now ask "how can that be? This is a good question, and can be answered by considering, as we discussed above, the all important aspect of "time". Even though the biomass may be small, the RATE at which new biomass is produced may be very large. Thus over time it is the amount of new biomass that is produced, from whatever the standing stock of biomass might be, that is important for the next trophic level.
We can examine this further by constructing a pyramid of energy , which shows rates of production rather than standing crop. Once done, the figure for the ocean would have the characteristic pyramid shape see Figure 4-bottom. Algal populations can double in a few days, whereas the zooplankton that feed on them reproduce more slowly and might double in numbers in a few months, and the fish feeding on zooplankton might only reproduce once a year.
Thus, a pyramid of energy takes into account the turnover rate of the organisms, and can never be inverted. Note that this dependence of one trophic level on a lower trophic level for energy is why, as you learned in the lectures on predation, the prey and predator population numbers are linked and why they vary together through time with an offset.
Figure 4: Pyramids of numbers, biomass, and energy for various ecosystems. The Residence Time of Energy. We see that thinking about pyramids of energy and turnover time is similar to our discussions of residence time of elements.
But here we are talking about the residence time of "energy". This difference in residence time between aquatic and terrestrial ecosystems is reflected in the pyramids of biomass, as discussed above, and is also very important to consider in analyzing how these different ecosystems would respond to a disturbance, or what scheme might best be used to manage the resources of the ecosystem, or how you might best restore an ecosystem that has been degraded e.
Humans and Energy Consumption All of the animal species on Earth are consumers, and they depend upon producer organisms for their food. For all practical purposes, it is the products of terrestrial plant productivity and some marine plant productivity that sustain humans.
What fraction of the terrestrial NPP do humans use, or, "appropriate"? It turns out to be a surprisingly large fraction, which launches us immediately into the question of whether this appropriation of NPP by humans is sustainable. Let's use our knowledge of ecological energetics to examine this very important issue.
Why NPP? Because only the energy "left over" from plant metabolic needs is available to nourish the consumers and decomposers on Earth. In a cropland NPP and annual harvest occur in the same year. In forests, annual harvest can exceed annual NPP for example, when a forest is cut down the harvest is of many years of growth , but we can still compute annual averages. Note that the following estimates are being successively revised in the literature, but the approach to the problem is always the same.
Outputs: 2 Scenarios Total productivity of lands devoted entirely to human activities. This includes total cropland NPP, and also energy consumed in setting fires to clear land.
A high estimate is obtained by including lost productive capacity resulting from converting open land to cities, forests to pastures, and due to desertification and other overuse of land. This is an estimate of the total human impact on terrestrial productivity. Table 1 provides estimates of total NPP of the world.
There is some possibility that below-ground NPP is under-estimated, and likewise marine NPP may be underestimated because the contribution of the smallest plankton cells is not well known. Estimate of human harvest of grains and other plant crops is 1. This implies loss, spoilage, or wastage of 0. Our low estimate uses 2. Amount used for firewood, especially in tropics, is not. The table gives a low estimate. The total is The High Calculation: See Table 3 For the high estimate we now include both co-opted NPP and potential NPP lost as a consequence of human activities: a Croplands are likely to be less productive than the natural systems they replace.
If we use production estimates from savanna-grasslands, it looks like cropland production is less by 9 Pg. The total for the high estimate is This gives us Caveat: These estimates are based on best available data and are approximate. They probably give the correct order of magnitude. Table 3 : High calculation of NPP co- opted by humans.
Additions to Table 3 from processes that co-opt or degrade NPP. Process Amount Pg Previous terrestrial total Table 3 Moreover, although major fish stocks are heavily fished, and many coastal areas are severely polluted, human impact on the seas is less than on land.
However, we do know that except for some aquaculture systems, any marine or freshwater fishery that humans have used we have over-exploited, and often we have ruined the fishery. This has probably never occurred before in Earth's history. The consequences include environmental degradation, species extinctions, and altered climate. Is our use of primary productivity sustainable?
The Human "carrying capacity" on Earth is hard to estimate, because it depends upon affluence of a population and the technology supporting that population think back to your Ecological Footprint calculations in lab. Some people believe that "technology will save us", and that agricultural systems will become more efficient and that new genetics of plants will make production more efficient.
Unfortunately, and as we have seen in this and other lectures, there are true limits to primary production based on the amount of light energy available at Earth's surface, and the efficiency at which light energy can be converted into carbon during photosynthetic reactions.
Thus the limits to unchecked growth must be very near. Notice that the lower we as humans "feed" on the trophic chain, the more efficient the web of life becomes -- eating animals that eat animals that eat plants is a very inefficient use of solar energy. Simple systems, with low diversity of pieces and few moving parts, work best think cars, bridges, health-care plans.
This contrasts with ecosystems, where nature has solved this problem and evolved incredibly diverse, complex systems think tropical rain forests and coral reefs with millions of species.
These systems operate with efficiency and stability over time. One reason for this difference, or at least a starting point for discussion, is that natural systems are always limited by the food available for organisms. However, humans systems overall or on average are not yet limited by the food energy available. As this situation changes in the future with population growth and more demands on primary productivity, we know from our understaning of energy flow in natural systems that "Ecological Efficiency will get us in the end" - and that is the last take-home point for this lecture.
Typically the numbers and biomass of organisms decreases as one ascends the food chain. We can construct pyramids of biomass, energy, and numbers to represent the relative sizes of trophic levels in ecosystems. Pyramids can often be "inverted" as a consequence of high production rates at lower trophic levels. The human diet is derived from plant material. Primer on Photosynthesis. Review of main terms and concepts in this lecture. Suggested Readings. Format for printing.
Ecosystem Type. Surface area x 10 6 km 2. NPP Pg. Woodland, grassland, and savanna. Cultivated land. Human area. Other terrestrial chapparral, bogs, swamps, marshes. Subtotal terrestrial. Lakes and streams. Subtotal aquatic. NPP Co-opted Pg. Grazing land : Converted pastures Consumed on natural grazing lands Burned on natural grazing land Subtotal. Forest land : Killed during harvest, not used Shifting cultivation Land clearing Forest plantation productivity Forest harvests Subtotal.
Human-occupied areas. Aquatic ecosystems.
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