 Animals which flourish in these ecosystems, they are the reptiles, the amphibians and different types of mammals. Decomposers as in all the ecosystems are part of this ecosystem and these are mainly the fungi and the bacteria. Let us have a look on a grassland food chain. In a grassland diagram shows that the again source of the energy is sunlight which is coming through producers inside the ecosystem. There are plants which gets energy from the sunlight and convert this energy into ATP, the chemical form of energy and into the carbohydrates to make their body and to make their life processes possible. Then you can see a mole or a rat, a rodent, the primary consumer. These are common in these ecosystems and they eat upon the producers. The grasses, the leguminous plants, they eat upon the nuts, they eat upon the leaves and other parts of the grasses. So we call them primary consumers. These are the herbivores. Then the primary consumers are eaten up by the snakes. We know that reptiles inhabit the grasslands. Snake is a reptile. Snakes eat upon these rodents. So we call the snakes secondary consumers. In grasslands snakes are very common and they eat upon and of course the moles and shrews they are also very common. The snakes eat upon these moles, shrews or the rats, other types of rodents. Then there are hawks present in these ecosystems or there are eagles present in these ecosystems which eat upon the snakes. So we call them tertiary consumers because these hawks or the eagles they are getting their energy by acquiring a snake from the environment and snake itself is a secondary consumer. So we call it the hawk a tertiary consumer. We also call it secondary carnivore because it is eating a primary carnivore. Snake is a primary carnivore because it is eating herbivore animal that is a mole or a rat. So secondary consumer is a primary carnivore and the tertiary consumer is a secondary carnivore. As you can see that all of these organisms, so this is a food chain that is producer, a grass, a grass plant, primary consumer, a rat maybe another rodent, the secondary consumer, snake and the tertiary consumer the hawk. The energy actually is flowing unidirectionally from sunlight to the plant in the producer, from producer to the primary consumer, the mole or the rat, from primary consumer to secondary consumer because it is eating the primary consumer and utilizing it then to the tertiary consumer the hawk. And all of these organisms when they die or plants for example they shed their some parts, they become part of the soil, the land and here comes the decomposers. There are different types of insects, worms and bacteria which decomposes all of these organisms, their dead bodies or their fallen parts and convert them into different inorganic or organic compounds and these inorganic and organic compounds are again taken up by as you see the diagram the arrow shows that these are taken up by the producers. For example ammonia, nitrates, other forms of like phosphorus, sulfur or others and all of these are then of course present inside the soil and plants the producers they absorb these ingredients from the soil through their roots and they become part of them. So this is a generalized food chain in a grassland ecosystem. Let us have a look on another example of a food chain we take in an aquatic ecosystem, an ecosystem present in water, a water body. Equated ecosystem first of all we look at some properties, aquatic present in water, it is marked by water which is a liquid medium which is quite good to support life because we know that temperature is a limiting factor and water changes its temperature slowly. So water is a good medium for supporting life. Water may be fresh water or marine water that is the saltish water, fresh water have less salts, less dissolved salts present in it, marine water or brackish water have more dissolved salts present in it or may be in other forms. A lake for example is a fresh water, a sea is a brackish water, saltish water then light and temperature penetration is important in aquatic ecosystems. Light is a very important factor in aquatic ecosystems because we know that the entry point of energy inside an ecosystem is always the sunlight. So the penetration of light inside the water in an aquatic ecosystem is extremely important. If the water body a lake, a sea, an ocean, a pound or a stream allows a good penetration of light then photosynthesis is possible and the producers can make energy. If there is lesser penetration of light then photosynthesis may be, may do not occur then the result will be like there will be two ways of handling it, one some organisms which are called chemotrophs they stay here, chemotrophs which make their energy and carbohydrates from in organic sources but they are fewer. So light penetration is a very important factor in the aquatic ecosystems and the temperature. Temperature stratification exist in water ecosystems. In the upper layers usually because they are exposed to sunlight they have higher temperatures. The lower layers, layers towards the bottom because they are quite far away from the sunlight because there is a top layer of water between them and the sunlight so they are comparatively colder. The life forms which are living in these water bodies depend upon all of these properties. Now we have, we go to a diagram and we look at the aquatic food chains. The organisms which are the producers in an aquatic ecosystem may be, they may be plant or they may be called some smaller organisms called phytoplankton, plant like organisms. Plants as you know they are producers, they convert sunlight into carbohydrates and energy. Phytoplankton are also plant like organisms, also some algae, some unicellular organisms they also have the capacity and the capability to carry out photosynthesis. Usually in the upper layers of water, the water body, a pound, a lake, an ocean, these organisms are present in abundance. On the shallow sides of the water, in those zones of the water body for example the lake where water is shallow, submerged and fully merged plants are present and these plants carry out photosynthesis. In more deeper regions where the lake is actually deep, these organisms, the phytoplankton are present in higher numbers. They have capacity, capability to carry out photosynthesis and they are the entry point of energy in an ecosystem. So there are lot many phytoplankton present in those parts in the upper layers of a lake in the deeper region. These phytoplankton are eaten up by small insects and crustaceans. There are lot many types of crustaceans, the shrimps, some water insects which are present in these water bodies, they eat upon the phytoplankton. These phytoplankton are the producers. These crustaceans and water insects, they are the primary consumers in a water ecosystem food chain. Then these crustaceans and insects, these are themselves consumed by the fish, the primary carnivore fish, different types of fishes. These fishes are themselves eaten up by the carnivore fishes. The large carnivore fishes which eat upon other fishes. So phytoplankton are producers which carry out photosynthesis, produces organic food. Crustaceans are the primary consumers that eat upon phytoplankton. Then fishes are secondary consumers that eat upon the crustaceans or the insects. Then other fishes which eat upon the carnivore fishes, they are the tertiary consumers in a water ecosystem. So this is how a water ecosystem food chain, it conducts the flow of energy from producers to consumers, the primary consumers. The crustaceans, the small insects, the water insects. Then comes the fishes and some other fishes. There could be another food chain that exists in the water ecosystem. For example phytoplankton produces the organic food. These are eaten up by the herbivore fishes. The fishes which eat upon the plant matter and then the herbivore fishes, they are eaten up by the primary carnivore fishes. Then some other fishes comes which eat upon those carnivore fishes which are eating the primary carnivores. They become the tertiary carnivore. So different types of food chains exist in different types of aquatic ecosystems. Now look at an Arctic ecosystem. You know that Arctic ecosystem is very, very cold. Arctic area is full of snow. Have a snowfall many times. Have very, very colder temperatures. Some specific life forms exist there. We look at a food chain in an Arctic ecosystem. On the base of the food chain you can see there are algae which are scattered and present in large numbers. Algae are the organisms which are also producers which have capability to convert the sunlight into food and into energy in the form of ATP. Then these algae are eaten up by the shrimps. Shrimps are the primary consumers or the herbivores. Shrimps are then eaten up by the cod fishes which are the secondary consumers or the primary carnivores of this ecosystem. Then the seals, seals eat upon the fishes, these carnivore fishes. So seals they make the secondary carnivores. Then comes the polar bears. Polar bears eat upon these seals and they make the tertiary consumer. So this is a food chain present in an Arctic ecosystem. To shrimp, to codfish, to seal and to a polar bear. Now we are going to talk about food webs. What are the food webs? We say food web. This is a network of eating and being eaten. Food chains are a straight relationship of eating and being eaten that is of energy flow. But in actuality, when there is an ecosystem and lot many organisms are living in that ecosystem, their relationships are actually much more complex than when exemplified by a simple food chain that is a straight relationship. For example, if there is a grass, a grass plant present in an ecosystem, this may be eaten by a goat, this may also be eaten by a dragon fly, this may also be eaten by a rodent and then the rodents, they make food for the snakes. Snakes eat the rodents, but rodents are also food of the owls, owls also eat upon the rodents, hawks sometimes may also eat the rodents. So the relationship, the feeding relationships between organisms are actually not as simple as a food chain. There are lot many food chains that do exist inside the ecosystem and then these food chains also interact with each other to make a web or a network of the relationship of the living organisms of feeding and that is of eating and being eaten by other organisms. So food web is actually a network of eating and being eaten. There are examples, we take certain examples of food webs from different types of ecosystems. From a grassland, forest, from aquatic ecosystem. The food web is basically a network of different organisms which have relationship of eating and being eaten with each other and these are, these food webs actually consist of interacting food chains. We take an example of a grassland ecosystem. We know that in a grassland ecosystem, there is a diverse, there is a diversity of life. There are diverse forms of animals present. There are amphibians, there are reptiles, there are mammals, there are different types of grasses but grass is eaten by most of the herbivores. There are different types of amphibians which also eat upon the grass. There are many reptiles like many lizards, they also eat upon the grass. So there are lot many organisms which are eating grass. Grass is a source of energy for all of these organisms. And these herbivore animals, all of these which are eating the grasses, they are themselves eaten up by more than one carnivores. For example, if there is an amphibian, a frog, it is not eaten up only by a snake, it may also be eaten up by an owl, by a fox. So the relationship becomes complex. Let us have a look on food web, an example. Look at this diagram. It shows that the grass which is present in an ecosystem is eaten up by a grasshopper. The same grass is eaten up by a rabbit and the same grass is eaten up by a mouse. The arrows shows the direction of energy flow. Then we see that grasshopper itself, so it means that the same grass, same grass plant is a source of food for a grasshopper, for a rabbit, for a mouse. Then we can see that the grasshopper itself is a source of food for a lizard because these lizards they eat upon these grasshopper. This grasshopper is also a source of food for a hawk. And we can see that the lizard which is eating upon the grasshopper, it is also a source of food for the hawk. So hawk is consuming both the grasshopper and the lizard. If we make two food genes, that is from grass to grasshopper to lizard to hawk, then we see producer, a primary carnivore, sorry a herbivore, then a primary carnivore the lizard and then a secondary carnivore the hawk. If we look at other way, then we can see that grass is eaten up by the grasshopper and grasshopper is directly eaten up by the hawk. The grasshopper is a herbivore and which is a primary consumer and the hawk makes then a secondary consumer and not the tertiary. Then we see that grass is eaten up by rabbit, herbivore and rabbit is eaten up by the hawk. So it is also a more simple food chain, then the mouse eats the grass and mouse is eaten up by the hawk, but there is another way of this food chain that the grass is eaten up by mouse, mouse is eaten up by the snake and snake is eaten up by the hawk. So all of these food chains in interaction with each other actually makes the food web, a complex relationship between the living organisms of being eaten and eating someone else. This is one example of a food web in a grassland ecosystem. We look at one more complex example here you can see in this diagram that there are producers and decomposers different types of and these producers if we look at start from producers then these producers the plants which are of various kinds these are eaten up by different types of organisms, a butterfly, a frog, a bird, a deer, a squirrel, lot money and then all of these organisms or we can say every one of these herbivores, these are all called will be called the herbivores, the primary consumers, every one of these primary consumers are eaten up by more than one secondary consumers, the carnivores. For example you can see that a raven is eating a butterfly, it is also eating a frog, it is also eating a bird. So secondary consumers they make various complex chains with the herbivores, the primary consumers and with the grasses. Then there are few tertiary consumers and these tertiary consumers as you can see like a bobcat, a big cat, a fox they are eating different types of secondary consumers and they are sometimes eating some primary consumers as well. This makes a more complex web of a diversified ecosystem. So if an ecosystem is more diversified in its life forms that is it have so many life forms, then the food webs or the feeding relationships present between its living community will be far more complex. So the complexity of a food web actually depends upon the complexity of life and the diversity of life. So more the diversity of life, more the complexity of the food webs. We look at an example of a food web from an aquatic ecosystem. Aquatic ecosystem we know as they are very suitable for life, they are suitable for different types of life forms. So aquatic ecosystems they have animals, they have plants, they have phytoplankton, they have soup plankton, they have decomposers. Their food webs are also usually very complex. Let us have a look on an example. As you can see in this diagram you can see two zones of water. One is the top zone, the other one is the bottom zone. In the top layer of water there is more penetration of light. There are different types of phytoplankton and the zoo plankton present. The phytoplankton are the producers which are utilizing the sunlight and the inorganic carbon, the carbon dioxide and converting it into organic form of carbon, the food. Then there are different types of fishes and the zoo plankton which are eating upon these different types of phytoplankton. For example, a fish is eating these phytoplankton and insect is eating the phytoplankton. And then we see that there are other fishes which are eating upon these fishes. We can see a bear which is present in the nearby areas and this is eating the fish as well because bears they also come to the waters and they also hunt the fishes. So you can see that there are different types of food chains that do exist in this ecosystem, the water ecosystem and they interact with each other and the same thing is eaten up by many other organisms and all those organisms they are eaten up by some other organisms. So in water also diverse types of food webs they do exist. Then we take another example of a desert ecosystem. Deserts as you know are hot dry climates. They are hot and they are dry because there is less rainfall. The deserts have few specific plants and few specific animals. Let us have a look on a food web. In this diagram you can see that there is sand and soil on the base. Then there are specific types of desert plants. These desert plants you can see are eaten up by different types of insects. These plants are also eaten up by the lizards, the reptiles. These are also eaten up by the rodents and these insects then themselves because these all of these insects the lizards and the rodents all of these makes the herbivores or the primary consumers. Then comes the secondary consumers the spiders, scorpions, different kinds of lizards they eat upon the insects. Then the lizard for example is eaten up by a hawk. The lizard is also eaten up by a fox. Then the herbivore lizards which eat upon plants they are eaten up by both fox and the hawk. The rodents different types of rodents which are herbivores which eat upon the plants they are eaten up by the snakes they are also eaten up by the hawks and the foxes directly and indirectly indirectly in this way that rodents eats upon plants snakes eat upon the rodents and then snakes are eaten up by the foxes and the hawks. So we can say that these rodents are directly eaten by the hawks and the foxes and they are indirectly through snakes eaten up by the foxes and the hawks. It means that complex relationship of food web food webs also does exist do exist in the desert ecosystems though desert ecosystems are comparatively less diverse in life because these are more hostile environments but you can see that even these environments lot many organisms can exist there is quite a good biodiversity and this diversity makes the complex relationship of eating and being eaten which is called a food web. This is another example of a food web in a desert ecosystem which shows again the producers at the base as usual the primary consumers different types of squirrels rodents and then secondary and some primary consumers then tertiary and some secondary consumers and then tertiary consumers some secondary consumers and some quaternary consumers. The food webs actually makes complex relationships between organisms for energy flow. The forest ecosystems are more rich in their biodiversity because they are more suitable for life. You can see in this diagram a relationship in the form of food web between organisms in a forest ecosystem there are trees which are eaten up by the deers by insects by rodents by birds rodents and birds are eaten up by the foxes and the owls. Deers are eaten up by the bears by large cats then the insects they are eaten up by the birds they are eaten up by the possum and so on. So, food webs are the complex networks which mark the relationship of different trophic levels at different trophic levels between the organisms of a specific area of a specific ecosystem. In today's lecture we talked about the food chains and the food webs we primarily covered the biotic components of an ecosystem then we talked about the food chains which are the straight relationships of energy flow between the organisms and we talked about food webs which are complex forms of energy flow and interaction of the food chains actually present in different types of ecosystem. We also talked about some examples from various ecosystems about their food chains and about their food webs.