Which ecosystem has the highest net primary productivity

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 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. The temperature affects the water availability in an ecosystem. If the temperature is too high there is an increased rate of evaporation and the water dries out easily and there is a scarcity of water.

If the temperature is ambient there is enough amount of water available for the use of the animals in an ecosystem.. Temperature Affects Density When the same amount of water is heated or cooled, its density changes. When the water is heated, it expands, increasing in volume. The warmer the water, the more space it takes up, and the lower its density.

Climate — low levels of rainfall and high temperatures lead to water deficits. When rainfall is low, there is less water available. When temperatures are high, water evaporates and so there is less available to use. Water surpluses are common where rainfall is high and temperatures are lower.

Water insecurity means that many girls living in some rural areas of developing countries can spend hours walking to collect water rather than attending school. Waterborne disease. Drinking or using dirty water puts people at risk of waterborne diseases and illnesses, such as diarrhoea, malaria and schistosomiasis. Does Topography Affect Water Quality? In fact, many individual factors that contribute to the quality of water are strongly impacted by topographical features.

Oxygen Content- The Oxygen content of any river body may change from the temperature of the water, or a rapid change in elevation such as a waterfall. In geomorphology, drainage systems, also known as river systems, are the patterns formed by the streams, rivers, and lakes in a particular drainage basin. They are governed by the topography of the land, whether a particular region is dominated by hard or soft rocks, and the gradient of the land.

Begin typing your search term above and press enter to search. Press ESC to cancel. Skip to content Home Sociology Which 3 ecosystems have the highest productivity? Ben Davis July 7, Which 3 ecosystems have the highest productivity?

What ecosystem has the highest net primary productivity? What causes high net primary productivity? What is the relationship of biomass to net primary productivity?

What is the process of net primary productivity? How can primary productivity be improved? What are three ways to measure primary productivity? The plants are too large in height so that the sunlight is not able to enter the forest.

Due to extreme heat and scarcity of rainfall , the Desert has one of the driest ecosystems and because of this reason very little diversity and plants are found in the desert. Various kinds of living animals, plants and microorganisms biotic , as well as non-living abiotic chemical and physical factors, are found in lakes and streams due to the freshness of water. Grassland occurs naturally and is dominated by grasses.

The plants that are found in Grassland do not grow much and are non-woody. Get Started for Free Download App. More Ecology and Functions of an ecosystem Questions Q1. The pyramid of energy in any ecosystem is. Where is the maximum bio-mass available?

Which of the following statement regarding efficiency of energy transfer through food webs is false? Population I. Part of the Earth consisting of all the ecosystem of the world B. Community II. Assemblage of all the individuals belonging to different species occurring in an area C. Ecosystem III. Group of similar individuals belonging to the same species found in an area D. Ecosphere IV.

Interaction between the living organisms and their physical environmental components V. Classification of organisms based on the type of environment. Match the following with correct options. Inexhaustible resources i.