What is the difference between photosynthetic efficiency and trophic efficiency

View Source herbivore. Secondary consumers Organisms that feeds on primary consumers in a food chain. They are carnivores meat-eaters and omnivores animals that eat both animals and plants. Any other animal or any plant that feeds on animals. Tertiary consumers [tertiary consumer]: An organism that feeds on secondary consumers in a food chain.

Most food webs cannot support more than four trophic levels, due to the inefficiency of energy transfer the loss of usable energy from one level to the next i. If the plants, microorganisms, and animals in a food web are categorized by their trophic levels, we can display and summarize their relationships, trophic level biomass, and energy transfer within a trophic pyramid Figure 5. Figure 5: A simple trophic pyramid demonstrates the loss of energy kilo calories, or biomass from one tropic level to the next.

Depicted as a pyramid, we can see that the primary producers or photosynthesizing autotrophs, make up the base of most food webs. In the trophic pyramid depicted in Figure 5, there are four trophic levels. At the base of the pyramid are the photosynthetic plants or primary producers. Note that the total biomass or stored energy of the base trophic level is many times greater than the other trophic levels, with each successive trophic level containing a significantly smaller total biomass.

Heterotrophs also are called consumers. In this lecture we will begin with a consideration of primary production, and in the next lecture we will examine what happens to this energy as it is conveyed along a food chain. The Process of Primary Production The general term " Production" is the creation of new organic matter. When a crop of wheat grows, new organic matter is created by the process of photosynthesis, which converts light energy into energy stored in chemical bonds within plant tissue.

This energy fuels the metabolic machinery of the plant. New compounds and structures are synthesized, cells divide, and the plant grows in size over time.

As was discussed in detail in a previous lecture, the plant requires sunlight, carbon dioxide, water, and nutrients, and through photosynthesis the plant produces reduced carbon compounds and oxygen.

Whether one measures the rate at which photosynthesis occurs, or the rate at which the individual plant increases in mass, one is concerned with primary production definition: the synthesis and storage of organic molecules during the growth and reproduction of photosynthetic organisms.

The core idea is that new chemical compounds and new plant tissue are produced. Over time, primary production results in the addition of new plant biomass to the system. Consumers derive their energy from primary producers, either directly herbivores, some detritivores , or indirectly predators, other detritivores.

Is there an Upper Limit to Primary Production? The short answer is "yes". Let's briefly consider how much energy is in fact captured by autotrophs, and examine how efficient is the process of photosynthesis.

Recall that the intensity of solar radiation reaching the earth's surface depends partly on location: the maximum energy intensity is received at the equator, and the intensity decreases as we move toward the poles. As we saw in the lecture on ecosystems, these differences have profound effects on climate, and lead to the observed geographic patterns of biomes. Furthermore, we know that only a small fraction of the sun's radiation is actually used in the photosynthetic reaction in plants at the Earth's surface.

Plants strongly absorb light of blue and red wavelengths hence their green color, the result of reflection of green wavelengths , as well as light in the far infrared region, and they reflect light in the near infrared region.

Even if the wavelength is correct, the light energy is not all converted into carbon by photosynthesis. Some of the light misses the leaf chloroplast, where the photsynthetic reactions occur, and much of the energy from light that is converted by photosynthesis to carbon compounds is used up in keeping the plant biochemical "machinery" operating properly - this loss is generally termed "respiration", although it also includes thermodynamic losses.

Plants do not, then, use all of the light energy theoretically available to them see Figure 2. Figure 2 : Reduction of energy available to plants On average, plant gross primary production on earth is about 5.

This is about 0. After the costs of respiration, plant net primary production is reduced to 4. This relatively low efficiency of conversion of solar energy into energy in carbon compounds sets the overall amount of energy available to heterotrophs at all other trophic levels.

Some Definitions So far we have not been very precise about our definitions of "production", and we need to make the terms associated with production very clear. Respiration can be further divided into components that reflect the source of the CO 2.

This will be discussed more in our lectures on climate change and the global carbon cycle. Note that in these definitions we are concerned only with "primary" and not "secondary" production. Secondary production is the gain in biomass or reproduction of heterotrophs and decomposers.

The rates of secondary production, as we will see in a coming lecture, are very much lower than the rates of primary production. To better understand the relationship between respiration R , and gross and net primary production GPP and NPP , consider the following example. This is your "gross production" of money, and it is analogous to the gross production of carbon fixed into sugars during photosynthesis.

That is the "cost" you pay to keep operating, and it is analogous to the respiration cost that a plant has when their cells use some of the energy fixed in photosynthesis to build new enzymes or chlorophyll to capture light or to get rid of waste products in the cell.

Measuring Primary Production You may already have some idea of how one measures primary production. There are two general approaches: one can measure either a the rate of photosynthesis , or b the rate of increase in plant biomass. Will they give the same answer?

The method used in studies of aquatic primary production illustrates this method well. In the surface waters of lakes and oceans, plants are mainly unicellular algae, and most consumers are microscopic crustaceans and protozoans. Both the producers and consumers are very small, and they are easily contained in a liter of water. If you put these organisms in a bottle and turn on the lights, you get photosynthesis. If you turn off the lights, you turn off the primary production.

However, darkness has no effect on respiration. Remember that cellular respiration is the reverse process from photosynthesis, as follows. When calculating the amount of energy that a plant stores as biomass, which is then available to heterotrophs, we must subtract plant respiration costs from the total primary production. The general procedure is so simple that primary production of the world's oceans has been mapped in considerable detail, and many of the world's freshwater lakes have also been investigated Figure 3.

One takes a series of small glass bottles with stoppers, and half of them are wrapped with some material such as tin foil so that no light penetrates. These are called the "light" and "dark" bottles, respectively. Figure 3. The bottles are filled with water taken from a particular place and depth; this water contains the tiny plants and animals of the aquatic ecosystem.

The bottles are closed with stoppers to prevent any exchange of gases or organisms with the surrounding water, and then they are suspended for a few hours at the same depth from which the water was originally taken. Inside the bottles CO 2 is being consumed, and O 2 is being produced, and we can measure the change over time in either one of these gases.

For example, the amount of oxygen dissolved in water can be measured easily by chemical titration. Then, the final value is measured in both the light and dark bottles after a timed duration of incubation. What processes are taking place in each bottle that might alter the original O 2 or CO 2 concentrations? The equations below describe them.

In this example we may also have some consumer respiration in both bottles, unless we used a net to sieve out tiny heterotrophs. Now consider the following simple example.

It illustrates how we account for changes from the initial oxygen concentrations in the water that occurred during the incubation. We will assume that our incubation period was 1 hour. The oxygen technique is limited in situations where the primary production is very low. In these situations, the radioactive form of carbon, C 14 14 CO 2 , can be used to monitor carbon uptake and fixation.

You can also convert the results between the oxygen and carbon methods by multiplying the oxygen values by 0. Consider the following example. Suppose we wish to know the primary production of a corn crop.

We plant some seeds, and at the end of one year we harvest samples of the entire plants including the roots that were contained in one square meter of area. We dry these to remove any variation in water content, and then weigh them to get the "dry weight". Thus our measure of primary production would be grams m -2 yr -1 of stems, leaves, roots, flowers and fruits, minus the mass of the seeds that may have blown away. What have we measured?

It isn't GPP, because some of the energy produced by photosynthesis went to meet the metabolic needs of the corn plants themselves. Is it NPP? Well, if we excluded all the consumers such as insects of the corn plant, we would have a measure of NPP.

But we assume that some insects and soil arthropods took a share of the plant biomass, and since we did not measure that share, we actually have measured something less than NPP. Note that this is exactly the same situation in the bottle method we described above if small heterotrophs that grazed on algae were included in the bottle, in which case the two methods would measure the same thing.

In recent years it has also become possible to estimate GPP and R in large plants or entire forests using tracers and gas exchange techniques. These measurements now form the basis of our investigations into how primary production affects the carbon dioxide content of our atmosphere.

Production, Standing Crop, and Turnover With either of these methods, the primary Production can be expressed as the rate of formation of new material, per unit of earth's surface, per unit of time. Standing crop , on the other hand, is a measure of the biomass of the system at a single point in time, and is measured as calories or grams per m 2. The difference between production and standing crop is a crucial one, and can be illustrated by the following question.

The rest of the energy passes out of the food chain in a number of ways: it is released as heat energy during respiration it is used for life processes eg movement it is egested in faeces or remains in dead organisms which are passed to decomposers Less energy is transferred at each level of the food chain so the biomass gets smaller.

How much energy is transferred from A to B? In other words, some ecosystems are more difficult to study than others; sometimes the quantification of energy transfers has to be estimated. Another main parameter that is important in characterizing energy flow within an ecosystem is the net production efficiency.

Net production efficiency NPE allows ecologists to quantify how efficiently organisms of a particular trophic level incorporate the energy they receive into biomass. It is calculated using the following formula:. Net consumer productivity is the energy content available to the organisms of the next trophic level.

Assimilation is the biomass energy content generated per unit area of the present trophic level after accounting for the energy lost due to incomplete ingestion of food, energy used for respiration, and energy lost as waste. Incomplete ingestion refers to the fact that some consumers eat only a part of their food. For example, when a lion kills an antelope, it will eat everything except the hide and bones.

The lion is missing the energy-rich bone marrow inside the bone, so the lion does not make use of all the calories its prey could provide. Thus, NPE measures how efficiently each trophic level uses and incorporates the energy from its food into biomass to fuel the next trophic level. In general, cold-blooded animals ectotherms , such as invertebrates, fish, amphibians, and reptiles, use less of the energy they obtain for respiration and heat than warm-blooded animals endotherms , such as birds and mammals.

The extra heat generated in endotherms, although an advantage in terms of the activity of these organisms in colder environments, is a major disadvantage in terms of NPE. Therefore, many endotherms have to eat more often than ectotherms to obtain the energy they need for survival. In general, NPE for ectotherms is an order of magnitude 10x higher than for endotherms.

For example, the NPE for a caterpillar eating leaves has been measured at 18 percent, whereas the NPE for a squirrel eating acorns may be as low as 1. It is widely accepted that the meat industry uses large amounts of crops to feed livestock. Because the NPE is low, much of the energy from animal feed is lost. Much of this difference is due to the low NPE of cattle.

Thus, there has been a growing movement worldwide to promote the consumption of non-meat and non-dairy foods so that less energy is wasted feeding animals for the meat industry. Ecological pyramids, which can be inverted or upright, depict biomass, energy, and the number of organisms in each trophic level.

The structure of ecosystems can be visualized with ecological pyramids, which were first described by the pioneering studies of Charles Elton in the s. Ecological pyramids show the relative amounts of various parameters such as number of organisms, energy, and biomass across trophic levels.

Ecological pyramids can also be called trophic pyramids or energy pyramids. Pyramids of numbers can be either upright or inverted, depending on the ecosystem. A typical grassland during the summer has an upright shape since it has a base of many plants, with the numbers of organisms decreasing at each trophic level. However, during the summer in a temperate forest, the base of the pyramid consists of few trees compared with the number of primary consumers, mostly insects.

Because trees are large, they have great photosynthetic capability and dominate other plants in this ecosystem to obtain sunlight. Even in smaller numbers, primary producers in forests are still capable of supporting other trophic levels. Ecological pyramids : Ecological pyramids depict the a biomass, b number of organisms, and c energy in each trophic level.

Another way to visualize ecosystem structure is with pyramids of biomass. This pyramid measures the amount of energy converted into living tissue at the different trophic levels. Using the Silver Springs ecosystem example, this data exhibits an upright biomass pyramid, whereas the pyramid from the English Channel example is inverted.

The plants primary producers of the Silver Springs ecosystem make up a large percentage of the biomass found there. However, the phytoplankton in the English Channel example make up less biomass than the primary consumers, the zooplankton.

As with inverted pyramids of numbers, the inverted biomass pyramid is not due to a lack of productivity from the primary producers, but results from the high turnover rate of the phytoplankton. The phytoplankton are consumed rapidly by the primary consumers, which minimizes their biomass at any particular point in time.

However, since phytoplankton reproduce quickly, they are able to support the rest of the ecosystem.