Satellite measurements of ocean colour have shown variable decade-scale trends in marine primary production, including a short-term increase in primary production in the Arctic Ocean from to Shorterterm trends were related to climate oscillations, while the long-term declines were most strongly related to increasing sea-surface temperatures — which leads to less mixing of ocean waters, reducing the nutrient supply for phytoplankton.
The exceptions are the Arctic and Antarctic oceans, where the causes of the observed long-term decreases in primary production are less clear, but may be related to increased wind intensity. Key finding overview Primary production in Arctic Lakes Marine primary production.
Status and Trends. Status and Trends legend. Changes in primary productivity on land. Note: trends shown are statistically significant. Source: Ahern et al. The greatest increases were in the tropics, as a result of fewer clouds and increased exposure to the sun, and in high latitudes of the Northern Hemisphere, attributed to increased temperature and water availability.
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A storyboard full of texts and drawings to narrate one's country in an original manner: letting loose the imagination of children around the world in the edition. And for the winners, production of animated short films! It is defined as follows:. We have been speaking of sustainable behaviours to apply to our daily life, but what happens when we unplug and….
More than events were organised in 30 countries during the European Robotics Week November. Bread and flour are staple foods for many cultures around the world.
It is possible to produce flour from cereals…. Energy and environment. An example of gross primary productivity is the compartment diagram of energy flow within the Silver Springs aquatic ecosystem.
Because all organisms need to use some of this energy for their own functions such as respiration and resulting metabolic heat loss , scientists often refer to the net primary productivity of an ecosystem. The net productivity is then available to the primary consumers at the next trophic level. Learning Objectives Explain the concept of primary production and distinguish between gross primary production and net primary production.
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.
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
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