Ecology Part 2 - Trophic relationships

Hi, this is Mr. Judd and this is a corn snake. It can unhinge its jaw and take in its prey all in one bite. It also has these backwards pointing teeth, that help as the prey struggles so it can only go one way, and that's down. This video is about trophic relationships, or feeding relationships. Let's start off with a simple food chain. We have a five-link food chain here. And it shows the trophic levels, or feeding levels. The first level always has to be a producer - or a plant that makes the food. The food then goes up the food chain - and make sure you have your arrows going in the right direction. The arrows show the movement of materials and energy through a food chain. It starts with who makes it, and goes up through each of the trophic levels. One of the things you need to be able to do with a chain is make some predictions. So let's say we go on a rattlesnake round-up and we kill of all of the rattlesnakes . . . what effect would that have? The first effect is that the birds of prey, or the top carnivores, will have no more food because there are no more rattlesnakes. They might go locally extinct. Now let's talk about the mouse population. The mice, well, they were being eaten by the rattlesnakes. So no longer are they being eaten. Their numbers might go up. If the mouse population goes up, how is that going to effect the level below them? Well, there are going to be more mice and they are going to be eating more. So the next level, the herbivores, they might go down. And if the herbivore go down, they are going to be eating less plants and plants might go up. This is called trophic cascade. It is a series of events set in motion by a change in a food chain. A more accurate way to show the feeding relationships in an ecosystem is a food web. It is just a bunch of interconnected food chains. In this food web, let's focus on, say, the mice. Let's say their population goes down. What effect might that have? Well, the two things that feed on them - the foxes and the birds of prey - they might also go down. They have less food to eat. And if the mice go down, what they eat - the plants down here (it looks like grass) - their population might go up. You could follow this along. Everything that relies on the grass for food might then go up. So in a food web, the changes are a lot more complex. In fact the whole ecosystem becomes more stable because if one thing goes up or down, it doesn't have a drastic effect like it did in a food chain. That takes us to this really interesting infographic. It's called, "What are we Eating," and it is about the average American diet. The most interesting part to me is right here in the middle. And that is that in middle of the scale it shows that the average American eats almost 2000 pounds of food every year. The outise of this diagram shows the makeup of that food - all the different type of food that the average American is eating. So this might be an interesting, weird, fact. Almost 2000 pounds of food? Well we don't gain 2000 pounds every year. So what's going on here? Let's bring in our average American. And lets show the 2000 pounds of food going in their mouth. This is like our food chain. What happens in the food? . . . Well, a huge amount of it gets released as wastes. And that waste is either solid or liquid. One thing you might not think of but is true is that you actually exhale some that as carbon dioxide. It has some weight. So you are losing materials that way too. So those are the main two ways you are losing those materials. What about the energy? 2000 pounds of food has a lot of Calories, so in the energy side of this, you are using the energy for your metabolism. it is running your body. And all the while, you are losing heat. So heat is being released. The energy coming in is eventuallly lost as heat. And on balance the average American is gaining, yes I said gaining, 1 to 2 pounds of weight every year on average. So if you wanted to maintain a stable weight, you should probably be eating a little less than 2000 pounds, but not much, because most of that remember is going to be lost as waste carbon dioxide and the energy is going to be burned off by your metabolism and released as heat. The key point her is that you don't get to keep all the food they should eat. Let's take this concept to a natural ecosystem. We have the sun powering the producers, the plants. And let's say that they can make about 10,000 Calories, that's energy, 10.000 Calories worth of food. Now they are to be eaten by the herbivores, but do they get all of that energy? No. At every level, about 90 percent of the energy is lost; it is lost due to heat. Now I know that plants aren't warm blooded, but hey still lose heat energy through their own metablism, they have chemical reactions happening 24-7. So that leaves 10 percent left for the herbivores. So what is 10 percent of 10,000? That's pretty easy you just knock off of zero. Its about 1,000 Calories for the herbivores. It doesn't stop there because the hebiivores are also are releasing or losing about 90 percent of their energy. as heat. And that leaves only 10 percent of that left for the carnivores. So they are left with . . . I'll take off another zero . . . 100 Calories of food energy. And that is not very much when you consider that the producers in this ecosystem has 10,000 Calories. So the basic idea is that their is less and less energy available as you move up the trophic levels. Now let's take this to out original food chain This is a simplified version of it. We took the birds of prey out. But this, this, and this; these bars. They represent how much energy is available to each of the levels of the food chain or each of the trophic levels. It is measured in Joules, which is the metric unit for energy. You can see that in this diagram the plants have way more energy than all the rest of the trophic levels combined. At the very top there is only 10 Joules of energy left of energy for the rattlesnake. This is why food chains can't be very long. Eventually you are going to run out of food. The classic shape that this makes, you might see it this way, is what is called a trophic pyramid. A trophic pyramid shows the amount of energy available at each trophic level, and it gets less and less as you move up. The last thing I want to talk about is a similar pyramid thing except this is about biomass. and bio is life and mass is material, so this is living material. We are going to support 50 grams of human tissue. That is not a whole human it is just some portion of it. That human is eating chickens. But those chickens are eating grains so it takes, in this biomass pyramid, about 1500 grams of grain to support 50 grams of human tissue. So it takes a lot of plant to support a human. Let's bring this concept back to that infographic. And if you didn't notice, on first glance might notice it now when I draw this line. This line divides our diet. These are plant foods and these are animal foods. The question can be asked - which is the most efficient way to eat? Should you be eating plants or should you be eating animals? Well, in an ecological sense, if you eat plants have way more energy and nutrients and material available to you because of these plants could alternatively be fed to animals and then we could eat the animals, but their is a huge loss of energy and materials when you when you need higher up in the trophic levels. So that's trophic relationships I hope that's helpful.