Ecosystems

hi in this lesson will be talking about ecosystems which are made up of community of organisms and their environment. Now the biosphere is the sum of all ecosystems on earth. And when we look at ecosystems, we want to be thinking about energy and matter. Now the law of conservation of Energy says that energy cannot be created or destroyed. It can Onley be transferred and transformed, so energy will be transferred from the sun to photosynthetic organisms. And energy is very inefficiently transferred between organisms in an ecosystem. So most energy that moves through the ecosystem is gonna be lost is heat on. The main thing to bear in mind about energy in ecosystems is that energy is always moving through ecosystems. It doesn't stay in ecosystems. They need a constant influx of energy to keep them powered. Now matter, on the other hand, behaves differently. Conservation of matter says that matter cannot be created or destroyed and will remain constant in a closed system, meaning assuming, for example, that no matter can escape the earth, which obviously isn't true. Um, but let's just pretend that Earth is a closed system. That basically means that all of the matter that is taking part in this closed system will stay in this close system and none of it will be destroyed. It's just going to be moved around basically. So again. The main point is that energy flows through ecosystems and is continuously lost, whereas matter is recycled through ecosystems like you see here in the carbon cycle, where the carbon will be moved between various sources and we'll take a closer look at this in a little bit. But for now, let's turn the page.

trophic levels described the position and organism occupies on the food chain, and it's going to be determined by its feeding habits. Primary producers will be the foundation of these food chains, and that's because they're able to generate biomass from inorganic matter so that they can support all other trophic levels. So primary producers are gonna be autotrophs or self feeders. Thes air generally gonna be photosynthetic organisms, but they can also be chemo autotrophs like the archaea and bacteria that formed the foundations of the ecosystems around deep sea hydrothermal vents. Now primary consumers feed on primary producers, and these air usually gonna be things like herbivores that feed on plants. Now these and other consumers are considered hetero tropes because they're organisms that cannot fix carbon from inorganic sources like what happens in the Calvin cycle of photosynthesis. Now they indeed need to use carbon for growth, so they have to consume organic matter in many cases, consume other organisms. Now, secondary consumers are generally carnivores that feed on primary consumers, and tertiary consumers are carnivores that feed on other carnivores. So, as you can see, we are working our way up the food chain, and here in our little food chain model, we have our first level. This is our primary primary producer, our primary consumer here. A the second level, our secondary consumer here in this third level and our tertiary consumer here at this fourth level. So what is missing from this food chain? That is very important. That you can see over here are the D composers. So the autotrophs, the producers, they're going to get energy from the sun. And they're going to use that to create biomass that will feed herbivores. And those herbivores will feed carnivores. But the D composers are going to return all of that organic matter back into the nutrient pool. So they served on incredibly important role because they're going thio return matter back to be used by other living organisms. So they're kind of like the recyclers. Almost now. We call the d composers Detroit of wars because they eat detritus. They wore eat to trade us, and basically, they're just hetero tropes that consume detritus. And this detritus is just non living organic material. So dead organisms and organic wastes like feces, for example, Now the food chain like what we just saw, right here is linear network of those trophic levels, and we will often look at a grazing food chain, which is what we saw with this food chain right here, which is going to have primary consumers feeding on plants. But we can also make a decompose er food chain where the primary consumers are going to be actually feeding on Dead Plant Matter, and we call those primary D composers. Now food chains will be linked together both grazing and decomposing food chains into a food web, which is a much better representation off the interactions between the different trophic levels in an ecosystem. And here I have a picture of some nice primary D composers. These fungi that air going to eat dead plant matter. With that, let's turn the page.

top down control cascades. They're seen in ecosystems were a predator high on the food web is going to control prey populations. Now what we can see is a trophic cascade where the predator is going to lower the abundance of prey and then reduce the next trophic level from predation or in this case, that we're going to take a look at herbivorous. You see, the wolf population in Yellowstone used to keep the elk population in check. But due to over hunting of wolves for very terrible political reasons, the wolf population of Yellowstone was diminished to nothing. They were hunted to extinction, and then the elk population exploded. And this actually lead Thio. Um, you know, a lot of herbivorous, and it greatly reduced the vegetation in the area. So this was an example of a trophic cascade because those wolves were actually protecting the vegetation indirectly by controlling the elk population. Now, primary production is something we look at Nikko Systems and this is the synthesis of organic compounds from inorganic carbon dioxide. And usually we're going to see this in the form of photosynthesis. And you can see the reaction here, uh, in the Calvin cycle that will perform this carbon fixation. And we're gonna be looking at different measures of production. There is gross primary productivity's E, which is the amount of energy generated by primary producers in an area over time. So here we can see our gross primary productivity. It's just all the energy generated now. Ah, useful, uh, measure toe look at is the net primary productivity. So some of that energy that is generated by the plants is going to be used by the plants own respiration. So they're gonna be returning that carbon to co two Now what you're left with after you take the gross primary productivity and remove what the plants used for respiration is the net primary productivity. So that's the gross primary production minus the energy consumed by the primary producers own respiration. And you can think of this is the total amount of new biomass added by primary producers. Now, net ecosystem productivity looks at the total accumulation of new biomass after the respiration off all organisms. So here you can see the net ecosystem. Uh, productivity takes that neck. Primary productivity minus everything that gets diverted to the hetero troves. Respiration. So everything we're left with. All that biomass left over is the net ecosystem productivity now that let's go ahead and flip the page.

there are limiting factors to the productivity of ecosystems in aquatic ecosystems. Light penetration can limit primary production. However, nutrient availability is going to severely limit primary production in aquatic ecosystems and is going to really be the bottleneck. And this will in part be due to limiting nutrients, which are elements that limit production and if added, production will increase. Usually these air going to be nitrogen and phosphorus, but not always now in terrestrial ecosystems, temperature and water availability tend to be the main limiting factors, and soils also have limiting nutrients. And like Quantock ecosystems, these usually tend to be nitrogen and phosphorus. And here you can see a chart that shows the relative amounts of photosynthesis based on light intensity. Japan, as you can see when light is very low down in this area, photosynthesis just lum. It's You might also notice that photosynthesis starts to peter off when light intensity gets too high, which can be due to, you know, the damaging effects of all that light. Of course, that's not really going to be much of an issue in, uh, most marine ecosystems, where these guys were just gonna be happy to get some light. Now, coral reefs are the most productive bios per area, and they're also one of the most threatened. They actually Onley take up a very small portion of the earth and the only account for a small portion of the total productivity of the Earth. But they are still the most productive by OEMs per area. Now, the most productive marine ecosystems generally are near coasts due to the high nutrient availability there. Terrestrial ecosystems are actually far more productive than marine ecosystems, and this is probably due to the availability of light here. In this chart, you can see the most productive marine ecosystems, and you can see the there these areas in red concentrated in coastal waters. Now here you can see primary production in terrestrial environments, and hopefully you'll notice that it's the regions known as the tropics, that they're gonna have that very high primary productivity. Tropical rainforests actually contain the most productive terrestrial ecosystems in the world, and this is gonna be due to the year round warmth and rain. With that, let's go ahead and flip the page

secondary production is the amount of energy converted to new biomass by hetero troughs. And we're going to be looking at the production efficiency of hetero troughs, which is how much energy is stored in an organism from the food that it eats. Now, energy is stored after excreting a bunch of that is waste and using some for respiration. So this is usually very inefficient. And as you can see here, we have an example of secondary production where this frog is going to be ingesting food, it's going to assimilate it. I mean, you know, extract the nutrients and whatnot. Some of that energy is going to be lost due to respiration, and some is going to be wasted as feces. And, of course, a lot of these frogs, they're just gonna die. So you know, there goes that, But some some small amount is going to be added as new biomass, and that is going to represent the production efficiency now in ecosystems. We're gonna wanna look at the trophic efficiency, which is how much energy has passed between the trophic levels of the food web, and usually this is Onley about 10%. So this is highly inefficient. In fact, this could range from about 5 to 20% but 10% is just a good estimate toe work with, and it's nice round number. So if we assume that approximately 10% of the energy and biomass and one trophic level gets transferred to the next trophic level, we can construct what's called a pyramid of net production. That's going to show the net production of biomass at each level So we can see this, uh, you know, theme the energy transfer in this pyramid. So assuming that what the primary producers have, we'll just call that 100%. I'm actually gonna switch to read just so it shows up. So the primary producers, that's 100% right there. That means the primary consumers are only going to get about 10% of the total energy. That was, um, uh, you know, storage and biomass of primary producers. So those primary consumers only get 10% of this 100% of the bottom of the pyramid. Now, these secondary consumers get on Lee 1% of what was on the bottom of the pyramid because they only get 10% of the rung just below them from the primary consumers, so they get 10% of what the primary consumers got. But the primary consumers only got 10% so they're only getting 1% of this base of the pyramid. Likewise, the third level is only going to get 10.1% so you can see that this is incredibly inefficient now. We can also sometimes be interested in looking at a biomass pyramid, which is going to show the amount of biomass stored in living tissue at each trophic level. And hopefully from this energy pyramid. You guessed that most of the biomass is going to be concentrated at the bottom of these pyramids, and as we move up in trophic levels, it is going to get much, much smaller. Now with that, let's go ahead and flip the page.

one of the issues that can result from the fact that the transfer of energy and biomass up the pyramid is so inefficient is that molecules that accumulated biomass will actually concentrate at higher levels of the food web and these air going to be things that are not easily digested or excreted and will efficiently accumulate in trophic level. So these are often toxins, you know, stuff like heavy metal stuff that can't be broken down or digested by living systems now, because organisms have to consume almost 10 times as much food as tissue they produce. Due to that inefficiency, these molecules are going to concentrate a higher levels. And that is why we call this bio magnification. So you can see here at this base level of the producers, you know, there's only a couple of these molecules, but then these primary consumers, they're going to eat so much of those primary producers to generate their new biomass that they're going to accumulate mawr of those molecules than the previous trophic level had. And so it's going to get concentrated Mawr and Mawr as we move up in trophic levels. Now, fortunately, Primary D composers like bacteria archaea fungi and roundworms are going to decompose organic matter and return all this stuff to the ecosystem. So soil organic matter is going to be the component of soil that includes the D composers and the detritus that they are decomposing at its various stages of decomposition. When it's completely decayed, we call it humans. This is, uh, formed from that completely decayed detritus, and it's super rich in nutrients. It's very good stuff for soil now. Decomposition cycles nutrients through the soil, and it generates forms of these nutrients that plants can uptake so that they can return them to the ecosystem. So let's actually go ahead, flip the page and look at some of these cycles.

Okay, everyone, in this lesson, we're gonna be talking about the water cycle. Now, I know you've probably all heard of the water cycle, but you may not know exactly what it entails. What type of process is this? Well, it's important to understand that the water cycle and many other cycles are bio geochemical cycles. What these are are pathways which chemical substances cycle through the A biotic and biotic components of the earth. So there is a water cycle. There's also a phosphorus cycle and a carbon cycle and many other different types of cycles that we'll talk about in later lessons. But these were going to be pathways and cyclic pathways that substances like water will take as they move throughout the atmosphere, the oceans, those streams, the rivers and the organisms. So it's like how water is recycled throughout our planet and this is a bio geochemical cycle, and there are other ones which we will learn more about later. So what's important to understand is that the water cycle is pretty much the most important bio geochemical cycle. Why? Because every living thing requires water to function. So the water cycle pretty important for life on earth, and basically the water cycle is going to be the flow of water above, on and below the earth's surface. So the water cycle is going to contain the different areas that water can exist. It can exist in the atmosphere via precipitation. It can exist on the ground in lakes and rivers and streams. It can exist inside of the ground, just aquifer zehr groundwater, and then it can also flow into the oceans as well. So this is going to be a depiction of the water cycle, as you can see here, and the water cycle has many different steps. But the major steps they're going to be that the oceans, obviously a ton of water there they're going to be have sun rays hitting them and that this is going to cause evaporation, turning liquid water into water vapor. And then this is going to go into the atmosphere and condense into clouds. So then the atmosphere has clouds, which are made of water vapor, and then when those clouds get very saturated with water, we're going to have precipitation, whether that be in the form of ice or snow or sleet or rain or anything like that that is gonna be water falling onto the earth, leaving the atmosphere and then going to the earth. And then a lot of things can happen from here. We can have streams fill with water. We can have water, seep into or infiltrate into the ground and become ground water. We can also have it collect in lakes and rivers and streams and usually groundwater. Rivers and legs are going to lead back into the ocean over time. And then that whole process is going to start again. Now there are some terms here that you might be, um, interested in, So the first one that we have that's a little bit different is sublimation. Sublimation is when a substance goes from a solid form directly into its vapor or gaseous form. So this would be for water for whenever it goes from ice into water. Vapor is very difficult to see water do this, and it doesn't do it all that often. You have to have very unique circumstances for this to happen, but this is called sublimation. Um, de sublimation is the exact opposite where water vapor turns directly into ice. But again, this is very difficult to see and you will probably never witnessed it. But if you were looking for a great example of sublimation, um, dry ice turns into carbon dioxide, but again, that is sublimation. But it's not water. Okay? Water sublimation is very difficult to visualize. And then there is another word here, which is very interesting. Evaporate transporation ev apple transpiration is actually a very specific form of evaporation off water from plants. This is the water vapor that plants release from their bodies. This is commonly called transpiration or EV apa transpiration. So a lot of our water and our atmosphere is also coming from plants as well. So that's what that term means. So now let's go down and let's talk about some specific types off water that are very important to life on Earth. So a very important type of water is groundwater. Any idea why? Because a lot of the fresh water that is utilized for life on our planet is going to be stored as ground water, especially for us human beings. A lot of our drinking water and our agricultural water for crops and livestock comes from ground water And what is groundwater It is water that sits underground inside soil or rock, and most of it is stored in a specific rocky structure called an aquifer. You've probably heard of an aquifer before, but you might not know exactly what it is. Basically, an aquifer is a layer of rock that is porous, meaning it has holes inside of it. So water permeable rock water can get into those holes in the rock and then be stored there for hundreds or thousands of years. So aqua furs are this poorest layer of stone that holds a ton off water. Now, in this image, up here, this line right here, let me see if I can pick a good color. This line that I'm drawing in red, This is representing groundwater. This is also representing groundwater, and that is water that just exists under the earth's surface. Now, the more specific type of groundwater in aqua furs that is going to be here. So this a confined aquifer right here is going to be that porous rock that is going to hold water inside of those holes in the rock. Now, whenever you are digging in the earth and you hit water, you're going to hit the water table. The water table is the level in the earth or in the ground that it's saturated with water. So basically, once you hit the water table, you've hit the top layer of groundwater, the water being held inside off the ground. And as you can see here, the water table is not very deep, and in many regions of the world, the water table is not very deep, and you can dig maybe 10 ft and hit water. It's a very high water table in these areas of the world. You probably won't build a basement, but in other areas of the world you can build a basement because the water table is not so high. So just understand that the water table is that very top layer of groundwater. So all of this is ground water here and then we have a specific aquifer, which is this porous, rocky structure that holds water. Now it's very important to understand that a lot of our water, especially in the United States, around 40 to 50% off the water we utilize for drinking and bathing, and for animals and our livestock and our crops comes from ground water, so it's very, very important. Okay, everyone, let's go on to our next topic

the carbon cycle is the flow of carbon through the a biotic and biotic components of the biosphere. And what's amazing about the carbon cycle is that photosynthesis removes a ton of CO two, and that amount is roughly equivalent to the amount of CO two that's added by cellular respiration. So in this way, these two processes feed each other. Cellular respiration produces CO two, and photosynthesis removes CO two to generate biomass. Now the major reservoirs of carbon include biomass soil, sediment, fossil fuels and in the atmosphere there is some carbon dioxide. Now the nitrogen cycle is particularly interesting, one because most nitrogen is actually found in the atmosphere and nitrogen is only able to enter ecosystems through this special process called nitrogen fixation, which will be carried out by organisms like bacteria. And this is going to be super important for supporting the growth of many primary producers, which need that nitrogen toe live. Now the phosphorus cycle tends to recycle locally in ecosystems unlike, for example, the water cycle or the carbon cycle that has very far reaching effects. The phosphorus cycle tends to stay pretty local because most phosphorus is found in rocks and soil, so it's not going to get too far. It's not going to travel too far. That's all I have for this one. I'll see you guys next time.