Making Sense of Ecosystem Production & Efficiency - Online Tutor, Practice Problems & Exam Prep

Ecosystems have an energy budget determined by primary producers, or autotrophs, which capture energy from the sun. This energy is transferred through trophic levels, with significant losses due to cellular respiration and waste. Key concepts include Gross Primary Productivity (GPP), Net Primary Productivity (NPP), Gross Consumer Productivity (GCP), and Net Consumer Productivity (NCP). Efficiency is measured through Net Production Efficiency (NPE) and Trophic Efficiency, highlighting that energy transfer averages around 10%. Understanding these concepts is crucial for grasping ecosystem dynamics and energy flow.

Making Sense of Ecosystem Production & Efficiency

In this video, we're going to be making sense of ecosystem production and efficiency terms that we already covered in our previous lesson videos. And so really there's no new information in this video. And if you're feeling really confident, then you can skip this video if you'd like to save some time. But if you're struggling even just a little bit, then stick around because this video could be really helpful for you as we take a look at this example and cover a handful of relevant terms all in the same video. And so that being said, let's go ahead and get started here.

So every single ecosystem has an energy budget, which is really the total amount of energy that the ecosystem has to work with. And the energy budget is going to be determined by primary producers or autotrophs, which are the organisms that initially captured the energy from the energy source. Now the energy captured by these primary producers is going to make its way up the food chain as that energy is transferred from one trophic level to the next trophic level. But what's really important for you to know is that not all of that energy will actually be utilized by organisms, and not all of the energy will be transferred from one trophic level to the next trophic level because energy is going to be lost along the way. And so in this example down below, we're going to be tracking the energy through the ecosystem.

Starting with the energy source, the sun, and tracking a subset of energy through the food chain, 3 trophic levels down to this bird. And so let's go ahead and enlarge this image so that we can see it more clearly and get started. So notice that we have the sidebar on the left hand side that you can use to track the energy through the ecosystem, starting with the sun and making our way through the food chain 3 trophic levels to this bird. And over here on the right hand side, we've got a corresponding image to go along with that sidebar. And down below, we have a key where you can see that assimilated energy is all of the energy inside of the dotted blue boxes on this sidebar.

And consumption is represented by the black arrows, cellular respiration represented by all of these purple arrows, and waste is represented by the brown arrows. Now there's quite a lot of information here on this slide, so let's go ahead and wipe it clean so that we can approach this one step at a time. And so, of course, the sun is going to serve as the primary source of energy for most ecosystems. And so just for the sake of an example, let's say that the sun is generating 400,000 kilojoules worth of energy per meter squared per month. Well, when it comes to primary producers like this plant here, it turns out that they only absorb a small fraction of the total solar energy because much of the energy is actually going to be reflected or it's simply not even going to hit photosynthesizing parts of the plant.

And so in many cases, only 1% of the total solar energy is absorbed. And so 1% of 400,000 kilojoules is just 4,000 kilojoules, and that initial amount of energy that's captured by this primary producer is what we call the gross primary productivity or the GPP, which is 4,000 kilojoules. Now this primary producer will need to perform its own cellular respiration. So let's say it loses 2,000 kilojoules worth of energy to cellular respiration, while the remaining amount of energy is going to be the plant's net primary productivity or NPP, which is 2,000 kilojoules. Now let's say that an insect like this grasshopper comes along and consumes 40% worth of this plant's biomass.

Well, 40% of the net primary productivity of 2,000 kilojoules is 800 kilojoules. And this initial amount of energy captured by this consumer is the gross consumer productivity or the GCP. Now this consumer will also need to perform cellular respiration and it will also lose waste as well. So let's say it loses 300 kilojoules to cellular respiration and 250 kilojoules to waste. Well, the leftover amount of energy is going to be this consumer's net consumer productivity or its NCP, which is 250 kilojoules.

So again, over here on the side bar, you can see the energy of respiration and waste being lost and the remaining net consumer productivity of 250 kilojoules here. Now let's say that a bird comes along and consumes 100% of the insect. Well, that means it's going to obtain 100% of the net consumer productivity or NCP of the insect, and that will be this bird's gross consumer productivity, the initial amount of energy that the bird obtains. And this bird, of course, is also going to need to perform cellular respiration, and it will also have waste. So let's say that it loses 220 kilojoules worth of energy for cellular respiration and has 10 kilojoules lost in waste.

Well, the leftover remaining amount of energy is this bird's net consumer productivity, which is 20 kilojoules here. And again, we can see this all over here on the sidebar. And so essentially, we've tracked this energy through the ecosystem. We started with 400,000 kilojoules worth of energy and just 3 trophic levels away in this particular example were boiled down to just 20 kilojoules worth of energy. So much of the energy has been lost along the way with every energy transfer.

So now that we've tracked the energy through the ecosystem, let's focus on energy efficiency. So let's focus on net production efficiency or NPE. Recall that net production efficiency is going to be the portion of assimilated energy that's used for net productivity. So all we need to do is take the net productivity and divide it by the assimilated energy and then multiply by a 100%. And we can calculate the NPE for every single trophic level.

So notice over here on the left, we have the NPE calculations for each trophic level. Again, taking the net productivity, dividing it by the assimilated energy, which again is inside of the blue boxes, and then multiplying it by a 100%. And when you do that for each of these trophic levels, this is the answer that you get: 50% NPE for the plant, 45% NPE for the insect, and 8.3% NPE for the bird. And so by looking at these NPE levels, you can see that the NPE can vary drastically from organism to organism. Now recall that trophic efficiency can only be calculated across trophic levels.

We can calculate one trophic efficiency from the plant to the insect and a second trophic efficiency from the insect to the bird. And trophic efficiency is just a ration of the net productivity. So we can get it by performing these calculations here. For the trophic efficiency from the plant to the insect, we take the net productivity of the insect and divide it by the net productivity of the plant. So 250 divided by 2,000, multiply by a 100%.

And then to get the trophic efficiency across these two trophic levels from insect to bird, again, we do the same thing. We take the net productivity of the bird divided by the net productivity of the insect, multiply it by a 100%. And when you perform these calculations, these are the answers that you get, 12.5% across the plant to the insect and 8% from the insect to the bird. And recall that trophic efficiencies tend to be right around 10% on average. So when you take the average of 12.5 and 8, it comes out to just about 10%.

So that's to be expected in most cases. So this here concludes our lesson. Hopefully, this was helpful for you, and moving forward, we'll be able to apply these concepts and continue to learn more about ecosystems. So I'll see you all in our next video.

Which of the following terms describes NPP?

• A. Total energy captured by primary producers in an ecosystem.
• B. Energy invested in the production of new biomass by autotrophs.
• C. Energy invested in new biomass by primary consumers.
• D. None of the above.

If a capybara has a net production efficiency of 15% and consumes 1800 kJ of grass in a day, 1150 kJ of which is assimilated, roughly how much energy will be converted to new biomass?

• A. 120 kJ.
• B. 270 kJ.
• C. 77 kJ.
• D. 173 kJ.

Financial Analogy for Ecosystem Production & Efficiency

In this video, we're going to cover a financial analogy for ecosystem production and efficiency just to give you the option of a fresh new perspective and a different way to think about these same exact ideas that we've already talked about in our previous lesson videos. And so really there's no new information in this video. And so in this financial analogy, we're going to imagine that energy is money, and the source of this money is going to be a business. And we're going to track the money from this business through 2 trophic levels, a set of parents and their child. And of course, this financial analogy on the left-hand side is analogous to how energy actually flows through ecosystems here on the right-hand side.

And so let's go ahead and enlarge this image so that we can see things more clearly and let's wipe it clean so that we can take things one step at a time. And I'm blocking this box behind me here, so let me get out of your way so you can see things a little bit easier. Alright. So once again, we know that the source of money is going to be a business. Let's say it's generating $200,000 over some period of time.

Well, this source of money is going to be analogous to the source of energy in most ecosystems, which is the sun. Here, generating 200,000 kilojoules worth of energy. Now of all this money that the business generates, not all of that money is going to make its way to the employees. The employees only get a small fraction of the money that the business generates. Just like primary producers only capture a small fraction of the energy that the sun generates.

So here we can see that a small amount of that money is trickling down to the next trophic level, the set of parents, which are also employees to this business, and we can see that the parents' gross pay is only $2,000. That's analogous to the gross primary production or the GPP, which recalls the initial amount of energy that's captured by a primary producer. Here, 2,000 kilojoules. Now these parents are very responsible with their money, and they only generate insignificantly small amounts of waste, pretty much negligible, which recall is similar to what we talked about in our previous lesson videos for primary producers generating insignificantly small amounts of wastes. However, these parents do have a significant amount of expenses and bills that need to be paid.

Here, $1,000 worth of expenses, and these expenses are analogous to cellular respiration that must be performed by these primary producers. Here, 1,000 kilojoules worth of energy going to cellular respiration. Now the leftover amount of money after the expenses is going to be the parent's net pay, which is $1,000, and this is essentially the money that is available for making new purchases, if you will. Now the parent's net pay is analogous to the net primary production or the NPP, which we'll call the energy available producing new biomass. And it's also going to be the energy that's available to be consumed by the next trophic level.

Just like the parents' net pay is the amount of money available to be passed down to the next trophic level, their child. But the child isn't going to receive all of the parents' net pay, the child's only going to receive a small fraction of the parents' net pay. Just like consumers typically only consume a small fraction of the net primary production. And so here, once again, we can see a small amount of this money trickling down to the next trophic level, this child, and so this is the child's gross pay or the child's allowance, if you will, which is only $200 of the $1,000, still pretty good if you ask me. And that's analogous to the gross consumer production or the GCP, which is the initial amount of energy captured by the consumer.

Here, only 200 kilojoules. Now this child is not going to be nearly as responsible with its money as its parents are. So it is going to generate a significant amount of waste. It's going to waste a lot of money, a $100 here towards candy or video games or whatever else you might consider to be waste. And it's also going to have some expenses, some bills, maybe school lunches.

$67 going towards that. And so once again, expenses are analogous to cellular respiration, 67 kilojoules going to that, and the waste is, of course, analogous to the waste here, 100 kilojoules going to waste. Now the leftover amount of money after the expenses and the waste is going to be the child's net pay, and that's $33. This is essentially the money that's available for making new purchases. And that's analogous to the net consumer production or the NCP.

That's the energy available for the consumer's biomass, 33 kilojoules here. And so really, we can take a step back. We've followed all of this money and energy through, and the big takeaway here is that we started off with a lot of money and a lot of energy and just 2 trophic levels away. We went from $200,000 just to $33. So a lot of that money was lost along the way just like a lot of energy is lost along the way with every single energy transfer from trophic level to trophic level.

That's the big takeaway. So now that we followed the energy, let's focus our attention on energy efficiencies, specifically net production efficiencies and trophic efficiencies. So let's do those calculations right here in the middle. I'm going to go ahead and get out of the way since I'm right in the middle. So let's go ahead and do that.

There we go. So let's go ah... NPP available biomass energy + available respiration energy × 100% ...calculate the net production efficiencies for each of these trophic levels and calculate the trophic efficiency across these trophic levels. So first, recall net production efficiency is going to be the net productivity divided by the assimilated energy. So net productivity for this trophic level is going to be the net pay or the net primary production, which is 1,000. So we can go ahead and put that in here in the numerator.

That's going to be divided by the assimilated energy, which is the energy available for biomass and the energy available for respiration. So energy available for biomass is the net primary production, that's 1,000, plus the energy available for respiration is 1,000. So 1,000 plus 1,000 is 2,000. That's the assimilated energy that goes in the denominator. Multiply that by 100%, and what we get is the NPE is 50% for this first trophic level.

We can do the same for the bottom. Again, the net productivity is going to be the net pay,$33, or the net consumer production here. Again, 33 kilojoules. We'll put 33 in here. That's going to be over the assimilated energy, which is the energy available for biomass and for respiration.

Again, biomass energy is the net consumer production, that's 33, respiration is 67, so 67 +33 is 100. That's going to go in the denominator here, 100. Multiply that by 100%, and we get 33%. So that's the net production efficiency for this second trophic level. Now for trophic efficiency, we're going to take the ratio of the net productivities across these 2.

So we'll take the net productivity of the current or the latest trophic level or the net pay here, it's going to be 33. We can put that in the numerator here. Over the net productivity or net pay of the previous trophic level, that's 1,000, so we can put that in the bottom, and then multiply that by 100%. And when we do that, what we get is an answer of 3.3%. And so now we've calculated all of these energy efficiencies.

This video is over. Hopefully, this was helpful for you, and I'll see you on our next video.