Sakshi Education
Introduction
What is an Ecosystem?
An ecosystem consists of the biological community that occurs in some locale, and the physical and chemical factors that make up its non-living or abiotic environment. There are many examples of ecosystems -- a pond, a forest, an estuary and grassland. The boundaries are not fixed in any objective way, although sometimes they seem obvious, as with the shoreline of a small pond. Usually the boundaries of an ecosystem are chosen for practical reasons having to do with the goals of the particular study.
The study of ecosystems mainly consists of the study of certain processes that link the living, or biotic, components to the non-living, or abiotic, components. Energy transformations and biogeochemical cycling are the main processes that comprise the field of ecosystem ecology. As we learned earlier, ecology generally is defined as the interactions of organisms with one another and with the environment in which they occur. We can study ecology at the level of the individual, the population, the community, and the ecosystem.
An ecosystem is a community of organisms interacting with each other and with their environment such that energy is exchanged and system-level processes, such as the cycling of elements, emerge.
The ecosystem is a core concept in Biology and Ecology, serving as the level of biological organization in which organisms interact simultaneously with each other and with their environment. As such, ecosystems are a level above that of the ecological community (organisms of different species interacting with each other) but are at a level below, or equal to, biomes and the biosphere. Essentially, biomes are regional ecosystems, and the biosphere is the largest of all possible ecosystems.
Ecosystems include living organisms, the dead organic matter produced by them, the abiotic environment within which the organisms live and exchange elements (soils, water, atmosphere), and the interactions between these components. Ecosystems embody the concept that living organisms continually interact with each other and with the environment to produce complex systems with emergent properties, such that "the whole is greater than the sum of its parts" and "everything is connected". Despite the apparent contradictions that result from the flexibility of the ecosystem concept, it is just this flexibility that has made it such a useful and enduring concept.
History of the Ecosystem Concept:
The term "ecosystem" was first coined by Roy Clapham in 1930, but it was ecologist Arthur Tensley who fully defined the ecosystem concept. In his classic article of 1935, Tensely defined ecosystems as "The whole system, including not only the organism-complex, but also the whole complex of physical factors forming what we call the environment".
The ecosystem concept marked a critical advance in the science of ecology, as Tensely specifically used the term to replace the "super organism" concept, which implied that communities of organisms formed something akin to a higher-level, more complex organism—a mistaken conception that formed a theoretical barrier to scientific research in ecology. exchange of materials between living and nonliving parts) within the system is an ecosystem."
Ecosystem Structure and Function:
Components (structure) environment
It must also be noted that most ecosystems contain a wide diversity of species, and that this diversity should be considered part of ecosystem structure.
Ecosystem processes (function):
By definition, ecosystems use energy and cycle matter, and these processes also define the basic ecosystem functions. Energetic processes in ecosystems are usually described in terms of trophic levels, which define the role of organisms based on their level of feeding relative to the original energy captured by primary producers. As always, energy does not cycle, so ecosystems require a continuous flow of high-quality energy to maintain their structure and function. For this reason, all ecosystems are "open systems" requiring a net flow of energy to persist over time—without the sun, the biosphere would soon run out of energy!
Ecosystems also cycle phosphorus, sulfur and other elements. As biogeochemical cycles are defined by the exchange of matter between organisms and their environment, they are classic examples of ecosystem-level processes.
Producers, consumers and decomposers:
Producers:
Producers make their own food. They do not have to obtain energy from other organisms. They obtain their energy from the sun and make food with that energy through the process of photosynthesis. Producers may also be called autotrophs. Most producers are plants, but there are some small organisms that produce food through photosynthesis as well. Producers are at the beginning of any simple food chain. On the African savanna, examples of producers would be any of the plants that grow there.
Consumers:
Consumers cannot make food. They must find food and eat it to obtain energy. Consumers may also be called heterotrophs. There are both primary and secondary consumers. Primary consumers are the next link in a simple food chain. These are the plant eaters, or herbivores. They do not eat other animals. In addition to the antelope mentioned earlier, examples of primary consumers on the African savanna would be a wild boar or a giraffe.
Decomposers:
Decomposers are the waste managers of any ecosystem. They are the final link in a food web breaking down dead organic matter (DOM) from producers and consumers and ultimately returning energy to the atmosphere in respiration and inorganic molecules bake to the soil during decomposition. Decomposers can be divided into two groups based on their mode of nutrition.
Energy flow in the ecosystem:
The diagram above shows how both energy and inorganic nutrients flow through the ecosystem. We need to define some terminology first. Energy "flows" through the ecosystem in the form of carbon-carbon bonds. When respiration occurs, the carbon-carbon bonds are broken and the carbon is combined with oxygen to form carbon dioxide. This process releases the energy, which is either used by the organism (to move its muscles, digest food, excrete wastes, think, etc.) or the energy may be lost as heat. The dark arrows represent the movement of this energy. Note that all energy comes from the sun, and that the ultimate fate of all energy in ecosystems is to be lost as heat. Energy does not recycle!
To summarize: In the flow of energy and inorganic nutrients through the ecosystem, a few generalizations can be made:
Ecological succession:
How does an ecological community develop?
Ecological succession describes this process of development, identifying how the community began as well as how and when it stabilizes.
Definition:
Ecological succession is the term used to describe what happens to an ecological community over time. It refers to more or less predictable and orderly set of changes that happen in the composition or structure of ecological community. When you are born, your learn to crawl, then walk and then run. When you grow old, your body goes through certain predictable changes over a period of time as in your body grows taller, your hair grows longer, your mind and body develops. Similarly, when you plant a tree, it grows slowly and then grows bigger and bigger and bigger. Basically, it’s a predictable set of changes that are visible over a period of time. The time scale can be decades or even millions of years.
It is different from Ecological Evolution because the changes that occur aren’t evolutionary in nature, but they may be adaptive. It is based on the principle and knowledge that nothing in life ever remains the same, but that all habitats are in a process of constant change as a result of the inter-dependencies and reactions within the ecological system itself.
Types of Ecological Succession:
Succession may be initiated either by formation of new habitat (landslide or lava flow) or disturbance of already existing habitat (fires, land clearance). There are three recognized stages to ecological succession. Each covers a gradual process of change and development. They do not have hard and defined boundaries, and it is possibly for an ecological system to be in both stages at once during the transition period from one to another. The 3 stages of ecological succession are:
Stages of Ecological Succession: There are four main types of ecological succession
Pioneer species are the ones that thrive the new habitat at the beginning of ecological succession. Pioneer species are ‘r-selected’ species that are fast growing and well-dispersed. Early succession is therefore dominated by so called ‘r-selected’ species. As succession continues, more species enter the community and begin to alter the environment. These are called ‘k-selected’ species. They are more competitive and fight for resource and space. The species that are better suited for the modified habitat then begin to succeed the other species. These are superseded by newer set of species. This goes on till the stage of climax or equilibrium is achieved.
When succession reaches a climax, where community is dominated by stable and small number of prominent species and no other species can be admitted, that is called the state of equilibrium or the climax community.
Ecological Succession and Energy Balance:
The energy balance that is achieved defines the climax stage of ecological succession. This means that within this very stable ecological system, there is a balance between the life that is produced, and the life that is consumed. For example, there are enough animals to eat the extra seeds to prevent overgrowth that could choke out plants, but not enough to prevent some of the seeds from growing and continuing their cycle of life. The climax stage is stable, but not static. During the other stages, the balance of energy is not in place and there may be crises that develop as a result which will prolong the secondary stage. Ecosystem is only interrupted, it is not yet understood whether it returns to the secondary stage, or would still be considered at its climax of ecological succession.
Food chains, food webs and ecological pyramids:
A food chain is the path of food from a given final consumer back to a producer. For instance, a typical food chain in a field ecosystem might be:
grass ---> grasshopper --> mouse ---> snake ---> hawk
Note that even though I said the food chain is the path of food from a given final consumer back to a producer we typically list a food chain from producer on the left (or at the bottom) to final consumer on the right (or at the top). Note to international readers: In Hebrew or Aramaic, or other languages which are read right-to-left, is it customary to list the food chains in the reverse order? By the way, you should be able to look at the food chain above and identify the autotrophs and heterotrophs, and classify each as a herbivore, carnivore, etc. You should also be able to determine that the hawk is a quaternary consumer.
It is when we have a picture of a food web in front of us that the definition of food chain makes more sense. We can now see that a food web consists of interlocking food chains, and that the only way to untangle the chains is to trace back along a given food chain to its source.
The food webs you see here are grazing food chains since at their base are producers which the herbivores then graze on. While grazing food chains are important, in nature they are outnumbered by detritus-based food chains. In detritus-based food chains, decomposers are at the base of the food chain, and sustain the carnivores which feed on them. In terms of the weight (or biomass) of animals in many ecosystems, more of their body mass can be traced back to detritus than to living producers.
Ecological pyramids:
Ecological pyramids are diagrams that illustrate how ecologically important factors, such as energy, biomass, and population size, vary between trophic levels in an ecosystem. Traditionally, these diagrams place the primary producers (photosynthetic organisms such as plants) at the bottom and the highest trophic levels at the top of the diagram. The size of the portion of the diagram associated with each trophic level illustrates the amount of energy, biomass, or number of individuals found in each trophic level.
General concepts:
Energy flows through the food chain in a predictable way, entering at the base of the food chain, by photosynthesis in primary producers, and then moving up the food chain to higher trophic levels. Because the transfer of energy from one trophic level to the next is inefficient, there is less energy entering higher trophic levels. Thus, diagrams showing how much energy enters each trophic level will have a distinct pyramid shape. Thus, this diagram has become known as the energy pyramid.
Energy pyramid:
The energy pyramid shows how the amount of energy entering each level varies across trophic levels. In general, only about 10% of the energy entering a trophic level is transferred to the trophic level above it, so the energy pyramid always has a distinct step-like pattern with less energy entering each trophic level up the food chain.
The shape of the energy pyramid affects the length of food chains because eventually the amount of energy entering the highest trophic level is not large enough to support a higher trophic level.
Biomass pyramid:
The biomass pyramid shows how the biomass of living organisms varies across trophic levels. The shape of the biomass pyramid in any ecosystem depends on a number of factors. If the amount of biomass in a trophic level depends on the amount of energy entering that trophic level, then, all else being equal, the biomass pyramid should have the same shape as the energy pyramid. However, when biomass of primary producers is rapidly removed by herbivores the biomass of primary consumers (herbivores) in an ecosystem at any time may be greater than the biomass of primary producers (e.g. plants). Thus, the resulting biomass pyramid is not necessarily shaped like a pyramid.
Numbers pyramid:
The numbers pyramid shows how the number of individuals per trophic level varies across trophic levels. if the number of individuals in a trophic level is related to the amount of energy entering that level then the number of individuals per level should also show a pyramidal shape. However, many factors can influence this relationship including the shape of the biomass pyramid and the size of individuals. If the "biomass pyramid" is not shaped like a pyramid then it is unlikely that the "numbers pyramid" will either. Furthermore, when insect herbivores are feeding on large trees, the difference in sizes between individuals in each level will cause there more individual herbivores than individual plants.
Author's cautionary note:
I suggest that students, teachers, and researchers take care when studying ecological pyramids. Diagraming how energy entering a level varies across trophic level will always show a pyramid shape, so that calling this relationship "the energy pyramid" is accurate and therefore a useful concept. However, diagraming how numbers and biomass varies across trophic levels often does not always produce a pyramid shape, so referring to these relationships as "the biomass pyramid" and "the numbers pyramid" is potentially misleading and likely to be a source of confusion. I suggest that the terms "trophic distribution of biomass" and "trophic distribution of numbers" be used instead. I know that these terms don't roll off of the tongue as easily as “biomass pyramid" and "numbers pyramid", but they are more accurate and might lead to more clear communication and understanding of this topic.
Introduction, types, characteristic features, structure and function of the following ecosystem: Forest ecosystem, Grassland ecosystem, Desert ecosystem, Aquatic ecosystems (ponds, streams, lakes, rivers, oceans, estuaries)
Forest ecosystem:
Forest ecosystem is the scientific study of the interrelated patterns, processes, flora, fauna and ecosystems in forests. The management of forests is known as forestry, silviculture, and forest management. A forest ecosystem is a natural woodland unit consisting of all plants, animals and micro-organisms (Biotic components) in that area functioning together with all of the non-living physical (abiotic) factors of the environment. The forest ecosystem is very important.
(i) Insects of the Tropical Rain Forest:
The most feared and well known spider in the world resides in the jungle. Ta¬rantulas are one of the creepiest animals you will ever see. Most species of tarantula have poisonous fangs for killing prey and for protection.
Although some are life-threatening to humans, others are harmless. Army ants are just one species of ant in the rain forest. They are called army ants because they march in a long, thick line through the jungle. They only stop when the young larvae reach pupil stage. Once the queen lays its eggs, the ants start marching again.
Beautiful butterflies fill the forest, but at one time these insects weren’t so pretty. Butterflies start out as caterpillars, which tend to be a tad on the ugly side. They go through metamorphosis, which is the process of changing into a butterfly. Centipedes aren’t so lucky. They don’t turn into butterflies, but in¬stead roam the forest looking for food. Some centipedes use poison to kill their prey.
(ii) Tropical Rain Forest Birds:
The birds of the rain forest are the most beautiful in the world. A wide range of colors can be seen darting through the trees as the forest tops come to life. Many species of tropical birds are kept as pets because of their looks.
Hoatzins are terrible flyers – crash landings are common practice. The brown kiwi is a flightless bird that looks more like a rodent with a long beak and feathers. Kiwis live on the ground instead of the trees. They have special claws used for running, digging and defense.
(iii) Tropical Rain Forest Mammals:
Birds aren’t the only creatures that fly through the rain forests. Several species of flying mammals live in the jungle. From the harmless fruit bat to the unique flying squirrel, the tropical rain forests are full of surprises.
The Indian flying fox is one of the largest bats in the world. Its wings can spread out to 5 feet in width. Unlike bats in other parts of the world, these bats do not live in caves. They prefer to .hang in trees during the day. Hundreds or even thousands of bats can be spotted in a single tree.
Vampire bats live in the Amazon jungle in South America. The famous stories of blood-sucking bats probably originated here. These bats do in fact drink the blood of their victims. They usually attack farm animals, but have also enjoyed the blood of humans. But vampire bats only drink a very small amount of fluid.
(iv) Tropical Rain Forest Reptiles:
The tropical rain forests of the world are full of reptiles. Reptiles are cold blooded, which means their body temperature depends on their environment. So, it is important for them to stay in warm climates. Snakes are reptiles, and the rain forests are home to many. The mamba family is the most poisonous of all. They kill their prey by injecting poison with their sharp fangs.
(v) Tropical Rain Forest Primates:
Monkeys and their cousins are all primates. Humans are also primates. There are many species of monkeys in the tropical rain forests of the world. Monkeys can be divided into two groups: new world monkeys and old world monkeys. New world monkeys live only in South and Central America. Spider monkeys live in the rain forests in the Andes Mountains.
They look very strange with their long noses. Spider monkeys eat mostly fruit and nuts, so they are called frugivores. They are joined by the howler monkeys. These primates are so named because they have a special sac that makes their sounds louder.
Old world monkeys live only in Africa and Asia. The colobus monkey is one such kind. These monkeys are called folio ores because they eat leaves. They live in small groups of 15, but other primates live in larger groups of up to 200. There are too many species. Chimpanzees, orangutans and gorillas are all called pongids. These primates are more famous than the others. Gorillas are too big to climb trees, so they are found on the forest floor.
Structure of Forest Ecosystems:
Different organisms exist within the forest layers. These organisms interact with each other and their surroundings. Each organism has a role or niche in sustaining the ecosystem.
Some provide food for other organisms; others pro¬vide shelter or control populations through predation:
Producers:
All living organisms intake energy in order to survive. In a forest ecosystem, trees and other plants get their energy from sunlight. Plants produce their own food, in the form of carbohydrates. Plants are, therefore, called the primary producers, since they produce the basic foodstuffs for other organisms within food chains and food webs. Photosynthesis is the chemical reaction that allows plants to produce their own food.
Consumers:
Animals cannot produce their own food. They must consume food sources for die energy they need to survive. All animals, including mammals, insects, and birds, are called consumers. Consumers rely on plants and other animals as a food source. Details of these animals in a forest ecosystem have been given earlier.
Primary consumers only eat plants and are referred to as herbivores. Second¬ary consumers are referred to as carnivores and feed on herbivores. Tertiary consumers are carnivores that feed on other carnivores. Omnivores eat both plant and animal matter.
Decomposers:
Leaves, needles, and old branches fall to the forest floor as trees grow. Eventu¬ally all plants and animals die. So what happens to all of this plant and animal material? Does it sit on the forest floor forever? Thankfully no. These materials are decomposed by worms, microbes, fungi, ants, and other bugs.
Decomposers break these items down into their smallest primary elements to be used again. Decomposers are important in that they sustain the nutrient cycle of ecosystems.
Humans are part of Forest Ecosystem:
Humans are consumers. We get food and materials from forests. Because of this, we are a part of the forest ecosystem. Human consumption alters forest ecosystems. Human intervention may be necessary to sustain forest communi¬ties under the increased pressure of human use.
Grassland ecosystem:
A grassland ecosystem is the collection of plants, animals and micro-organisms that live within an environment where grasses are the primary form of vegetation. Examples of grassland ecosystems include the prairies of western North America, the Pampas of Argentina and the Russian steppes.
Desert ecosystem:
Types and Characteristic Features:
One can find at least one desert on every continent except Europe and Antarc¬tica. Each desert is different in some way, but they all have one thing in com¬mon. In order for an area of land to be considered a desert, it must receive less than 10 inches of water a year.
How come deserts get such little water? Clouds are scarce in these regions, and we all know that without clouds, there can’t be rain, snow or any other precipi¬tation. But clouds also serve another purpose – they block out some of the Sun. The desert gets mighty hot during the day because the Sun beats down on the sand. At night, the desert gets very cold, because there aren’t clouds around to keep the heat from escaping to the atmosphere.
Structure and Function:
The different components of a desert ecosystem are:
(A) Abiotic Component:
The abiotic component includes the nutrients present in the soil and the aerial environment. The characteristic feature of the abiotic component is lack of or¬ganic matter in the soil and scarcity of water.
(B) Biotic Component: The various biotic components representing three functional groups are:
(a) Producer organisms:
The producers are mainly shrubs or bushes, some grasses and a few trees. Surprisingly, there are many species of plants that survive in the desert. Most of them are succulents, which mean they store water. Others have seeds that lay dormant until a rain awakens them. Regardless, these plants find a way to get water and protect themselves from the heat.
The most famous desert plant is the cactus. There are many species of cacti. The saguaro cactus is the tall, pole shaped cactus. The saguaro can grow up to 40 feet tall. It can hold several tons of water inside its soft tissue. Like all cacti, the saguaro has a thick, waxy layer that protects it from the Sun.
(b) Consumers:
These include animals such as insects and reptiles. Besides them, some rodents, birds and some mammalian vertebrates are also found.
Desert Insects and Arachnids:
There are plenty of insects in the desert. One of the most common and destruc¬tive pests is the locust. A locust is a special type of grasshopper. They travel from place to place, eating all the vegetation they find. Locusts can destroy many crops in a single day.
There are also several species of ants in the desert. The harvester ants gather seeds and store them for use during the dry season. And the honey pot ants have a very weird habit. Some members of the colony eat large amounts of sugar, so much that their abdomens get too large for them to move. The rest of the colony feeds off this sugar.
There are also arachnids in the desert. Spiders are the most notable arachnids, but scorpions also belong in this group. Some species of scorpions have poison in their sharp tails. They sting their predators and their prey with the piercing tip.
Desert Reptiles:
Reptiles are some of the most interesting creatures of the desert. Reptiles can withstand the extreme temperatures because they can control their body tem¬peratures very easily. You can put most of the desert reptiles into one of two categories: snakes and lizards.
Many species of rattlesnakes can be found in the desert. Rattlesnakes have a noisy rattle they use to warn enemies to stay away. If the predator isn’t careful, the rattlesnake will strike, injecting venom with its sharp fangs. Other desert snakes include the cobra, king snake and the hognose.
Lizards make up the second category of desert reptiles. They are probably the most bizarre looking animals in the desert. While some change colors and have sharp scales for defense, others change their appearance to look more threaten¬ing.
Desert Birds:
Like the other inhabitants of the desert, birds come up with interesting ways to survive in the harsh climate. The sand grouse has special feathers that soak up water. It can then carry the water to its young trapped in the nest.
Other birds, like the gila woodpecker, depend on the giant saguaro as its home. This woodpecker hollows out a hole in the cactus for a nest. The cool, damp inside is safe for the babies.
The roadrunner is probably the most well known desert bird. Roadrunners are so named because they prefer to run rather than fly. Ostriches also prefer to use their feet. Even the young depend on walking to find food and water. The galah is one of the prettiest desert birds. It is one of the few species that return to the same nest year after year.
Galahs are interesting birds, in that the number of eggs they lay depends on the climate. If the desert is in a drought, they don’t lay any. However, during more tolerable years, the galah may lay as many as five eggs.
Desert Mammals:
There are several species of mammals in the desert. They range in size from a few inches to several feet in length. Like other desert wildlife, mammals have to find ways to stay cool and drink plenty of water. Many desert mammals are burrowers.
Camels – The Cars of the Desert:
Camels could be included in the mammal section. Camels are the cars of the desert. Without them, people would have great difficulty crossing the hot ter¬rain. There are two types of camels: Bactrian and dromedary. The main differ¬ence between the two is the number of humps. Dromedaries have one hump, and Bactrian have two. Both kinds are used by people, but only Bactrian’s are found in the wild.
Camels are great for transportation because they use very little water. Camels can withstand very high temperatures without sweating. They also store fat in their humps for food. If a Bactrian camel travels a long distance without eating, its hump will actually get smaller.
(c) Decomposers:
Due to poor vegetation the amount of dead organic matter is very less. As a result the decomposers are very few. The common decomposers are some bacte¬ria and fungi, most of which are thermopile.
Aquatic Ecosystems:
Most of the water on our planet is in the oceans that cover 71 percent of Earth's surface. Less than 1 percent of all the water is considered freshwater, and most of that is frozen in the polar ice caps. The study of freshwater aquatic ecosystems, limnology, has often been separated from the study of marine systems, oceanography. Although freshwater and marine ecosystems are extremely diverse in structure, all of the plants and animals must live in or on water. The physical constraints and opportunities for life in water, and how all of these living organisms interact with each other in a liquid medium, give a unifying theme to aquatic studies.
The Influence of Water:
Water is a liquid and has a greater density and viscosity than air. It can absorb a large amount of solar radiation with a small increase in temperature. Once heated, it will get cooler at a slower rate than land. Aquatic organisms are therefore somewhat buffered against massive, rapid changes in temperature. Aquatic organisms, however, may have to adapt to the water temperature in hot freshwater springs, to the hot vents in the ocean floor in volcanic areas, and to the chilling cold of the water of the polar oceans and freezing winters in the temperate zones of the world. Cold water is denser than hot water, and this may lead to massive mixing and turnover in lakes.
In rivers and streams, the water depth and the water flow rate will determine the structure of the biological communities. Plants have to be attached and be highly specialized in structure to survive in fast-flowing water. In larger bodies of water, such as lakes and oceans, wind and tides will mix waters and carry sediments and organisms over large distances. Wave action will alter the physical structure and the geography of shores and coastlines and have a tremendous effect on the biological communities that can survive there.
What is an Ecosystem?
An ecosystem consists of the biological community that occurs in some locale, and the physical and chemical factors that make up its non-living or abiotic environment. There are many examples of ecosystems -- a pond, a forest, an estuary and grassland. The boundaries are not fixed in any objective way, although sometimes they seem obvious, as with the shoreline of a small pond. Usually the boundaries of an ecosystem are chosen for practical reasons having to do with the goals of the particular study.
The study of ecosystems mainly consists of the study of certain processes that link the living, or biotic, components to the non-living, or abiotic, components. Energy transformations and biogeochemical cycling are the main processes that comprise the field of ecosystem ecology. As we learned earlier, ecology generally is defined as the interactions of organisms with one another and with the environment in which they occur. We can study ecology at the level of the individual, the population, the community, and the ecosystem.
An ecosystem is a community of organisms interacting with each other and with their environment such that energy is exchanged and system-level processes, such as the cycling of elements, emerge.
The ecosystem is a core concept in Biology and Ecology, serving as the level of biological organization in which organisms interact simultaneously with each other and with their environment. As such, ecosystems are a level above that of the ecological community (organisms of different species interacting with each other) but are at a level below, or equal to, biomes and the biosphere. Essentially, biomes are regional ecosystems, and the biosphere is the largest of all possible ecosystems.
Ecosystems include living organisms, the dead organic matter produced by them, the abiotic environment within which the organisms live and exchange elements (soils, water, atmosphere), and the interactions between these components. Ecosystems embody the concept that living organisms continually interact with each other and with the environment to produce complex systems with emergent properties, such that "the whole is greater than the sum of its parts" and "everything is connected". Despite the apparent contradictions that result from the flexibility of the ecosystem concept, it is just this flexibility that has made it such a useful and enduring concept.
History of the Ecosystem Concept:
The term "ecosystem" was first coined by Roy Clapham in 1930, but it was ecologist Arthur Tensley who fully defined the ecosystem concept. In his classic article of 1935, Tensely defined ecosystems as "The whole system, including not only the organism-complex, but also the whole complex of physical factors forming what we call the environment".
The ecosystem concept marked a critical advance in the science of ecology, as Tensely specifically used the term to replace the "super organism" concept, which implied that communities of organisms formed something akin to a higher-level, more complex organism—a mistaken conception that formed a theoretical barrier to scientific research in ecology. exchange of materials between living and nonliving parts) within the system is an ecosystem."
Ecosystem Structure and Function:
Components (structure) environment
It must also be noted that most ecosystems contain a wide diversity of species, and that this diversity should be considered part of ecosystem structure.
Ecosystem processes (function):
By definition, ecosystems use energy and cycle matter, and these processes also define the basic ecosystem functions. Energetic processes in ecosystems are usually described in terms of trophic levels, which define the role of organisms based on their level of feeding relative to the original energy captured by primary producers. As always, energy does not cycle, so ecosystems require a continuous flow of high-quality energy to maintain their structure and function. For this reason, all ecosystems are "open systems" requiring a net flow of energy to persist over time—without the sun, the biosphere would soon run out of energy!
Ecosystems also cycle phosphorus, sulfur and other elements. As biogeochemical cycles are defined by the exchange of matter between organisms and their environment, they are classic examples of ecosystem-level processes.
Producers, consumers and decomposers:
Producers:
Producers make their own food. They do not have to obtain energy from other organisms. They obtain their energy from the sun and make food with that energy through the process of photosynthesis. Producers may also be called autotrophs. Most producers are plants, but there are some small organisms that produce food through photosynthesis as well. Producers are at the beginning of any simple food chain. On the African savanna, examples of producers would be any of the plants that grow there.
Consumers:
Consumers cannot make food. They must find food and eat it to obtain energy. Consumers may also be called heterotrophs. There are both primary and secondary consumers. Primary consumers are the next link in a simple food chain. These are the plant eaters, or herbivores. They do not eat other animals. In addition to the antelope mentioned earlier, examples of primary consumers on the African savanna would be a wild boar or a giraffe.
Decomposers:
Decomposers are the waste managers of any ecosystem. They are the final link in a food web breaking down dead organic matter (DOM) from producers and consumers and ultimately returning energy to the atmosphere in respiration and inorganic molecules bake to the soil during decomposition. Decomposers can be divided into two groups based on their mode of nutrition.
- Detritivores are organisms that ingest non-living organic matter. These can include earthworms, beetles and many other invertebrates.
- Saprotrophs are organism that lives on or in non- living organic matter, secreting digestive enzymes into it and absorbing the products of digestion. These include Fungi and bacteria.
Energy flow in the ecosystem:
The diagram above shows how both energy and inorganic nutrients flow through the ecosystem. We need to define some terminology first. Energy "flows" through the ecosystem in the form of carbon-carbon bonds. When respiration occurs, the carbon-carbon bonds are broken and the carbon is combined with oxygen to form carbon dioxide. This process releases the energy, which is either used by the organism (to move its muscles, digest food, excrete wastes, think, etc.) or the energy may be lost as heat. The dark arrows represent the movement of this energy. Note that all energy comes from the sun, and that the ultimate fate of all energy in ecosystems is to be lost as heat. Energy does not recycle!
To summarize: In the flow of energy and inorganic nutrients through the ecosystem, a few generalizations can be made:
- The ultimate source of energy (for most ecosystems) is the sun
- The ultimate fate of energy in ecosystems is for it to be lost as heat.
- Energy and nutrients are passed from organism to organism through the food chain as one organism eats another.
- Decomposers remove the last energy from the remains of organisms.
- Inorganic nutrients are cycled, energy is not.
Ecological succession:
How does an ecological community develop?
Ecological succession describes this process of development, identifying how the community began as well as how and when it stabilizes.
Definition:
Ecological succession is the term used to describe what happens to an ecological community over time. It refers to more or less predictable and orderly set of changes that happen in the composition or structure of ecological community. When you are born, your learn to crawl, then walk and then run. When you grow old, your body goes through certain predictable changes over a period of time as in your body grows taller, your hair grows longer, your mind and body develops. Similarly, when you plant a tree, it grows slowly and then grows bigger and bigger and bigger. Basically, it’s a predictable set of changes that are visible over a period of time. The time scale can be decades or even millions of years.
It is different from Ecological Evolution because the changes that occur aren’t evolutionary in nature, but they may be adaptive. It is based on the principle and knowledge that nothing in life ever remains the same, but that all habitats are in a process of constant change as a result of the inter-dependencies and reactions within the ecological system itself.
Types of Ecological Succession:
Succession may be initiated either by formation of new habitat (landslide or lava flow) or disturbance of already existing habitat (fires, land clearance). There are three recognized stages to ecological succession. Each covers a gradual process of change and development. They do not have hard and defined boundaries, and it is possibly for an ecological system to be in both stages at once during the transition period from one to another. The 3 stages of ecological succession are:
- Primary –
This is when an ecological community first enters into a new form of habitat that it has not been present in before. A good example of this would be the habitat created when granite is removed in a quarry. The rock face that is left behind is altered and becomes a new habitat. The environment that then grows within that habitat is considered to be in its primary stage.
- Secondary –
The secondary succession stage occurs after a habitat has been established, but it is then disturbed or changed in some fashion and a new community moves in. To use the example from before – let us say that a primary stage develops on the face of a newly quarried granite cliff. That habitat grows undisturbed, until there is a forest fire that then burns and changes a portion of the habitat that has been growing on the rock face. That ecological habitat has now entered its secondary stage.
- Climax –
The climax stage is the last stage of an ecosystem. It is when the ecosystem has become balanced and there is little risk of an interfering event or change to mutate the environment. Several rainforests and deserts qualify as being in the climax stage. What is tricky about a climax stage is that given human development, any ecosystem that is in the climax stage now holds the risk of being destroyed and going backward in the stages.
Stages of Ecological Succession: There are four main types of ecological succession
- Pioneer-
Pioneer types are the new life forms that enter into a primary succession and begin to take hold. This can be anything from a seed to bacteria to an insect or to an animal wandering into a new area and bedding down to make it their home. The pioneer has no connection to the environment, but it does find enough present in the new ecosystem to begin to establish its life.
- Establishing:
The establishing type can be hard to pinpoint because it crosses into the pioneer and sustaining. Establishing is the process in which life forms identify elements in an ecosystem that can sustain their basic needs – such as food, water and safe habitat.
- Sustaining:
Sustaining type means that life in the ecosystem has begun to enter into a pattern that allows for a cycle of life to continue. This means that birth and death are occurring, and there is little migration outside of the ecosystem – this is most common in the climax succession.
- Producing:
The producing type occurs during the secondary succession. This is when life forms are breeding and growing, but there is migration because what is produced is also not capable of being supported within the ecosystem. There are also more areas of overgrowth or overpopulation due to seed levels.
Pioneer species are the ones that thrive the new habitat at the beginning of ecological succession. Pioneer species are ‘r-selected’ species that are fast growing and well-dispersed. Early succession is therefore dominated by so called ‘r-selected’ species. As succession continues, more species enter the community and begin to alter the environment. These are called ‘k-selected’ species. They are more competitive and fight for resource and space. The species that are better suited for the modified habitat then begin to succeed the other species. These are superseded by newer set of species. This goes on till the stage of climax or equilibrium is achieved.
When succession reaches a climax, where community is dominated by stable and small number of prominent species and no other species can be admitted, that is called the state of equilibrium or the climax community.
Ecological Succession and Energy Balance:
The energy balance that is achieved defines the climax stage of ecological succession. This means that within this very stable ecological system, there is a balance between the life that is produced, and the life that is consumed. For example, there are enough animals to eat the extra seeds to prevent overgrowth that could choke out plants, but not enough to prevent some of the seeds from growing and continuing their cycle of life. The climax stage is stable, but not static. During the other stages, the balance of energy is not in place and there may be crises that develop as a result which will prolong the secondary stage. Ecosystem is only interrupted, it is not yet understood whether it returns to the secondary stage, or would still be considered at its climax of ecological succession.
Food chains, food webs and ecological pyramids:
A food chain is the path of food from a given final consumer back to a producer. For instance, a typical food chain in a field ecosystem might be:
grass ---> grasshopper --> mouse ---> snake ---> hawk
Note that even though I said the food chain is the path of food from a given final consumer back to a producer we typically list a food chain from producer on the left (or at the bottom) to final consumer on the right (or at the top). Note to international readers: In Hebrew or Aramaic, or other languages which are read right-to-left, is it customary to list the food chains in the reverse order? By the way, you should be able to look at the food chain above and identify the autotrophs and heterotrophs, and classify each as a herbivore, carnivore, etc. You should also be able to determine that the hawk is a quaternary consumer.
It is when we have a picture of a food web in front of us that the definition of food chain makes more sense. We can now see that a food web consists of interlocking food chains, and that the only way to untangle the chains is to trace back along a given food chain to its source.
The food webs you see here are grazing food chains since at their base are producers which the herbivores then graze on. While grazing food chains are important, in nature they are outnumbered by detritus-based food chains. In detritus-based food chains, decomposers are at the base of the food chain, and sustain the carnivores which feed on them. In terms of the weight (or biomass) of animals in many ecosystems, more of their body mass can be traced back to detritus than to living producers.
Ecological pyramids:
Ecological pyramids are diagrams that illustrate how ecologically important factors, such as energy, biomass, and population size, vary between trophic levels in an ecosystem. Traditionally, these diagrams place the primary producers (photosynthetic organisms such as plants) at the bottom and the highest trophic levels at the top of the diagram. The size of the portion of the diagram associated with each trophic level illustrates the amount of energy, biomass, or number of individuals found in each trophic level.
General concepts:
Energy flows through the food chain in a predictable way, entering at the base of the food chain, by photosynthesis in primary producers, and then moving up the food chain to higher trophic levels. Because the transfer of energy from one trophic level to the next is inefficient, there is less energy entering higher trophic levels. Thus, diagrams showing how much energy enters each trophic level will have a distinct pyramid shape. Thus, this diagram has become known as the energy pyramid.
Energy pyramid:
The energy pyramid shows how the amount of energy entering each level varies across trophic levels. In general, only about 10% of the energy entering a trophic level is transferred to the trophic level above it, so the energy pyramid always has a distinct step-like pattern with less energy entering each trophic level up the food chain.
The shape of the energy pyramid affects the length of food chains because eventually the amount of energy entering the highest trophic level is not large enough to support a higher trophic level.
Biomass pyramid:
The biomass pyramid shows how the biomass of living organisms varies across trophic levels. The shape of the biomass pyramid in any ecosystem depends on a number of factors. If the amount of biomass in a trophic level depends on the amount of energy entering that trophic level, then, all else being equal, the biomass pyramid should have the same shape as the energy pyramid. However, when biomass of primary producers is rapidly removed by herbivores the biomass of primary consumers (herbivores) in an ecosystem at any time may be greater than the biomass of primary producers (e.g. plants). Thus, the resulting biomass pyramid is not necessarily shaped like a pyramid.
Numbers pyramid:
The numbers pyramid shows how the number of individuals per trophic level varies across trophic levels. if the number of individuals in a trophic level is related to the amount of energy entering that level then the number of individuals per level should also show a pyramidal shape. However, many factors can influence this relationship including the shape of the biomass pyramid and the size of individuals. If the "biomass pyramid" is not shaped like a pyramid then it is unlikely that the "numbers pyramid" will either. Furthermore, when insect herbivores are feeding on large trees, the difference in sizes between individuals in each level will cause there more individual herbivores than individual plants.
Author's cautionary note:
I suggest that students, teachers, and researchers take care when studying ecological pyramids. Diagraming how energy entering a level varies across trophic level will always show a pyramid shape, so that calling this relationship "the energy pyramid" is accurate and therefore a useful concept. However, diagraming how numbers and biomass varies across trophic levels often does not always produce a pyramid shape, so referring to these relationships as "the biomass pyramid" and "the numbers pyramid" is potentially misleading and likely to be a source of confusion. I suggest that the terms "trophic distribution of biomass" and "trophic distribution of numbers" be used instead. I know that these terms don't roll off of the tongue as easily as “biomass pyramid" and "numbers pyramid", but they are more accurate and might lead to more clear communication and understanding of this topic.
Introduction, types, characteristic features, structure and function of the following ecosystem: Forest ecosystem, Grassland ecosystem, Desert ecosystem, Aquatic ecosystems (ponds, streams, lakes, rivers, oceans, estuaries)
Forest ecosystem:
Forest ecosystem is the scientific study of the interrelated patterns, processes, flora, fauna and ecosystems in forests. The management of forests is known as forestry, silviculture, and forest management. A forest ecosystem is a natural woodland unit consisting of all plants, animals and micro-organisms (Biotic components) in that area functioning together with all of the non-living physical (abiotic) factors of the environment. The forest ecosystem is very important.
(i) Insects of the Tropical Rain Forest:
The most feared and well known spider in the world resides in the jungle. Ta¬rantulas are one of the creepiest animals you will ever see. Most species of tarantula have poisonous fangs for killing prey and for protection.
Although some are life-threatening to humans, others are harmless. Army ants are just one species of ant in the rain forest. They are called army ants because they march in a long, thick line through the jungle. They only stop when the young larvae reach pupil stage. Once the queen lays its eggs, the ants start marching again.
Beautiful butterflies fill the forest, but at one time these insects weren’t so pretty. Butterflies start out as caterpillars, which tend to be a tad on the ugly side. They go through metamorphosis, which is the process of changing into a butterfly. Centipedes aren’t so lucky. They don’t turn into butterflies, but in¬stead roam the forest looking for food. Some centipedes use poison to kill their prey.
(ii) Tropical Rain Forest Birds:
The birds of the rain forest are the most beautiful in the world. A wide range of colors can be seen darting through the trees as the forest tops come to life. Many species of tropical birds are kept as pets because of their looks.
Hoatzins are terrible flyers – crash landings are common practice. The brown kiwi is a flightless bird that looks more like a rodent with a long beak and feathers. Kiwis live on the ground instead of the trees. They have special claws used for running, digging and defense.
(iii) Tropical Rain Forest Mammals:
Birds aren’t the only creatures that fly through the rain forests. Several species of flying mammals live in the jungle. From the harmless fruit bat to the unique flying squirrel, the tropical rain forests are full of surprises.
The Indian flying fox is one of the largest bats in the world. Its wings can spread out to 5 feet in width. Unlike bats in other parts of the world, these bats do not live in caves. They prefer to .hang in trees during the day. Hundreds or even thousands of bats can be spotted in a single tree.
Vampire bats live in the Amazon jungle in South America. The famous stories of blood-sucking bats probably originated here. These bats do in fact drink the blood of their victims. They usually attack farm animals, but have also enjoyed the blood of humans. But vampire bats only drink a very small amount of fluid.
(iv) Tropical Rain Forest Reptiles:
The tropical rain forests of the world are full of reptiles. Reptiles are cold blooded, which means their body temperature depends on their environment. So, it is important for them to stay in warm climates. Snakes are reptiles, and the rain forests are home to many. The mamba family is the most poisonous of all. They kill their prey by injecting poison with their sharp fangs.
(v) Tropical Rain Forest Primates:
Monkeys and their cousins are all primates. Humans are also primates. There are many species of monkeys in the tropical rain forests of the world. Monkeys can be divided into two groups: new world monkeys and old world monkeys. New world monkeys live only in South and Central America. Spider monkeys live in the rain forests in the Andes Mountains.
They look very strange with their long noses. Spider monkeys eat mostly fruit and nuts, so they are called frugivores. They are joined by the howler monkeys. These primates are so named because they have a special sac that makes their sounds louder.
Old world monkeys live only in Africa and Asia. The colobus monkey is one such kind. These monkeys are called folio ores because they eat leaves. They live in small groups of 15, but other primates live in larger groups of up to 200. There are too many species. Chimpanzees, orangutans and gorillas are all called pongids. These primates are more famous than the others. Gorillas are too big to climb trees, so they are found on the forest floor.
Structure of Forest Ecosystems:
Different organisms exist within the forest layers. These organisms interact with each other and their surroundings. Each organism has a role or niche in sustaining the ecosystem.
Some provide food for other organisms; others pro¬vide shelter or control populations through predation:
Producers:
All living organisms intake energy in order to survive. In a forest ecosystem, trees and other plants get their energy from sunlight. Plants produce their own food, in the form of carbohydrates. Plants are, therefore, called the primary producers, since they produce the basic foodstuffs for other organisms within food chains and food webs. Photosynthesis is the chemical reaction that allows plants to produce their own food.
Consumers:
Animals cannot produce their own food. They must consume food sources for die energy they need to survive. All animals, including mammals, insects, and birds, are called consumers. Consumers rely on plants and other animals as a food source. Details of these animals in a forest ecosystem have been given earlier.
Primary consumers only eat plants and are referred to as herbivores. Second¬ary consumers are referred to as carnivores and feed on herbivores. Tertiary consumers are carnivores that feed on other carnivores. Omnivores eat both plant and animal matter.
Decomposers:
Leaves, needles, and old branches fall to the forest floor as trees grow. Eventu¬ally all plants and animals die. So what happens to all of this plant and animal material? Does it sit on the forest floor forever? Thankfully no. These materials are decomposed by worms, microbes, fungi, ants, and other bugs.
Decomposers break these items down into their smallest primary elements to be used again. Decomposers are important in that they sustain the nutrient cycle of ecosystems.
Humans are part of Forest Ecosystem:
Humans are consumers. We get food and materials from forests. Because of this, we are a part of the forest ecosystem. Human consumption alters forest ecosystems. Human intervention may be necessary to sustain forest communi¬ties under the increased pressure of human use.
Grassland ecosystem:
A grassland ecosystem is the collection of plants, animals and micro-organisms that live within an environment where grasses are the primary form of vegetation. Examples of grassland ecosystems include the prairies of western North America, the Pampas of Argentina and the Russian steppes.
Desert ecosystem:
Types and Characteristic Features:
One can find at least one desert on every continent except Europe and Antarc¬tica. Each desert is different in some way, but they all have one thing in com¬mon. In order for an area of land to be considered a desert, it must receive less than 10 inches of water a year.
How come deserts get such little water? Clouds are scarce in these regions, and we all know that without clouds, there can’t be rain, snow or any other precipi¬tation. But clouds also serve another purpose – they block out some of the Sun. The desert gets mighty hot during the day because the Sun beats down on the sand. At night, the desert gets very cold, because there aren’t clouds around to keep the heat from escaping to the atmosphere.
Structure and Function:
The different components of a desert ecosystem are:
(A) Abiotic Component:
The abiotic component includes the nutrients present in the soil and the aerial environment. The characteristic feature of the abiotic component is lack of or¬ganic matter in the soil and scarcity of water.
(B) Biotic Component: The various biotic components representing three functional groups are:
(a) Producer organisms:
The producers are mainly shrubs or bushes, some grasses and a few trees. Surprisingly, there are many species of plants that survive in the desert. Most of them are succulents, which mean they store water. Others have seeds that lay dormant until a rain awakens them. Regardless, these plants find a way to get water and protect themselves from the heat.
The most famous desert plant is the cactus. There are many species of cacti. The saguaro cactus is the tall, pole shaped cactus. The saguaro can grow up to 40 feet tall. It can hold several tons of water inside its soft tissue. Like all cacti, the saguaro has a thick, waxy layer that protects it from the Sun.
(b) Consumers:
These include animals such as insects and reptiles. Besides them, some rodents, birds and some mammalian vertebrates are also found.
Desert Insects and Arachnids:
There are plenty of insects in the desert. One of the most common and destruc¬tive pests is the locust. A locust is a special type of grasshopper. They travel from place to place, eating all the vegetation they find. Locusts can destroy many crops in a single day.
There are also several species of ants in the desert. The harvester ants gather seeds and store them for use during the dry season. And the honey pot ants have a very weird habit. Some members of the colony eat large amounts of sugar, so much that their abdomens get too large for them to move. The rest of the colony feeds off this sugar.
There are also arachnids in the desert. Spiders are the most notable arachnids, but scorpions also belong in this group. Some species of scorpions have poison in their sharp tails. They sting their predators and their prey with the piercing tip.
Desert Reptiles:
Reptiles are some of the most interesting creatures of the desert. Reptiles can withstand the extreme temperatures because they can control their body tem¬peratures very easily. You can put most of the desert reptiles into one of two categories: snakes and lizards.
Many species of rattlesnakes can be found in the desert. Rattlesnakes have a noisy rattle they use to warn enemies to stay away. If the predator isn’t careful, the rattlesnake will strike, injecting venom with its sharp fangs. Other desert snakes include the cobra, king snake and the hognose.
Lizards make up the second category of desert reptiles. They are probably the most bizarre looking animals in the desert. While some change colors and have sharp scales for defense, others change their appearance to look more threaten¬ing.
Desert Birds:
Like the other inhabitants of the desert, birds come up with interesting ways to survive in the harsh climate. The sand grouse has special feathers that soak up water. It can then carry the water to its young trapped in the nest.
Other birds, like the gila woodpecker, depend on the giant saguaro as its home. This woodpecker hollows out a hole in the cactus for a nest. The cool, damp inside is safe for the babies.
The roadrunner is probably the most well known desert bird. Roadrunners are so named because they prefer to run rather than fly. Ostriches also prefer to use their feet. Even the young depend on walking to find food and water. The galah is one of the prettiest desert birds. It is one of the few species that return to the same nest year after year.
Galahs are interesting birds, in that the number of eggs they lay depends on the climate. If the desert is in a drought, they don’t lay any. However, during more tolerable years, the galah may lay as many as five eggs.
Desert Mammals:
There are several species of mammals in the desert. They range in size from a few inches to several feet in length. Like other desert wildlife, mammals have to find ways to stay cool and drink plenty of water. Many desert mammals are burrowers.
Camels – The Cars of the Desert:
Camels could be included in the mammal section. Camels are the cars of the desert. Without them, people would have great difficulty crossing the hot ter¬rain. There are two types of camels: Bactrian and dromedary. The main differ¬ence between the two is the number of humps. Dromedaries have one hump, and Bactrian have two. Both kinds are used by people, but only Bactrian’s are found in the wild.
Camels are great for transportation because they use very little water. Camels can withstand very high temperatures without sweating. They also store fat in their humps for food. If a Bactrian camel travels a long distance without eating, its hump will actually get smaller.
(c) Decomposers:
Due to poor vegetation the amount of dead organic matter is very less. As a result the decomposers are very few. The common decomposers are some bacte¬ria and fungi, most of which are thermopile.
Aquatic Ecosystems:
Most of the water on our planet is in the oceans that cover 71 percent of Earth's surface. Less than 1 percent of all the water is considered freshwater, and most of that is frozen in the polar ice caps. The study of freshwater aquatic ecosystems, limnology, has often been separated from the study of marine systems, oceanography. Although freshwater and marine ecosystems are extremely diverse in structure, all of the plants and animals must live in or on water. The physical constraints and opportunities for life in water, and how all of these living organisms interact with each other in a liquid medium, give a unifying theme to aquatic studies.
The Influence of Water:
Water is a liquid and has a greater density and viscosity than air. It can absorb a large amount of solar radiation with a small increase in temperature. Once heated, it will get cooler at a slower rate than land. Aquatic organisms are therefore somewhat buffered against massive, rapid changes in temperature. Aquatic organisms, however, may have to adapt to the water temperature in hot freshwater springs, to the hot vents in the ocean floor in volcanic areas, and to the chilling cold of the water of the polar oceans and freezing winters in the temperate zones of the world. Cold water is denser than hot water, and this may lead to massive mixing and turnover in lakes.
In rivers and streams, the water depth and the water flow rate will determine the structure of the biological communities. Plants have to be attached and be highly specialized in structure to survive in fast-flowing water. In larger bodies of water, such as lakes and oceans, wind and tides will mix waters and carry sediments and organisms over large distances. Wave action will alter the physical structure and the geography of shores and coastlines and have a tremendous effect on the biological communities that can survive there.
Published date : 13 Nov 2015 02:13PM
