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UNIT-2ECOSYSTEMS Q1) Explain the concept and structure of an ecosystem.A1) The ecosystem can be defined as, “a unit that includes all the organisms, i.e., the community in a given area interacting with the physical environment so that a flow of energy leads to clearly defined trophic structure, biotic diversity, and material cycles, i.e., exchange of materials between living and non-living, within the system”.The common characteristics of most of the ecosystems are as follows:1. The ecosystem is considered a major structural and functional unit of ecology.2. The structure of an ecosystem is related to its species diversity in the sense that a complex ecosystem has high species diversity.3. The function of an ecosystem is related to energy flow and material cycles within and outside the system.4. The relative amount of energy required to maintain an ecosystem depends on its structure. Complex ecosystems need less energy to maintain themselves.5. Young ecosystems develop and change from less complex to more complex ecosystems, through the process called succession.6. Each ecosystem has its energy budget, which cannot be exceeded.7. Adaptation to local environmental conditions is an important feature of the biotic components of an ecosystem, failing which they might get perished.8. The function of every ecosystem involves a series of cycles, e.g., water cycle, nitrogen cycle, oxygen cycle, etc. These cycles are run on energy. A continuation of the existence of an ecosystem requires the exchange of materials/nutrients to and from the different components.We can classify ecosystems as follows: (a) Natural Ecosystems:These ecosystems have the capability of operating and maintaining themselves without any major interference by man. A classification based on their habitat can further be made:1. Terrestrial ecosystems: forest, grassland, and desert.2. Aquatic ecosystems: freshwater ecosystem, viz. pond, lake, river, and marine ecosystems, viz. ocean, sea, or estuary.(b) Artificial Ecosystem:These are maintained by man. These ecosystems are manipulated by humans for different purposes, e.g., croplands, artificial lakes and reservoirs, townships, and cities.Structure of an ecosystem:Every ecosystem has non-living (abiotic) and living (biotic) components.Primary succession Primary succession starts in barren areas, such as on bare rock exposed by a retreating glacier. The first inhabitants are lichens or plants—those that can survive in such barren areas. For centuries, these “pioneer species” break down the rock into the soil that can support simple plants such as grasses. These grasses further modify the soil, which is then colonized by other types of plants. Each successive stage changes the habitat by altering the amount of shade and the composition of the soil. The final stage of succession is a climax community, which is a very stable stage that can survive for hundreds of years.Primary and secondary succession both create a continually changing mix of species within communities as disturbances of various intensities, sizes, and frequencies keep changing the area. The progression of species during succession, however, is not random. At every stage, certain species have evolved life histories to exploit the particular conditions of the community. This situation imposes a partially predictable sequence of change in the species composition of communities during succession. In the initial period, only a small number of species from surrounding habitats can thrive in a disturbed habitat. As new plant species spring out, they modify the habitat by altering such things as the amount of shade on the ground or the mineral composition of the soil. These changes allow other species that are more suitable for this modified habitat to succeed the old species. These newer species are superseded, in turn, by still newer species. A similar succession cycle of animal species keeps going, and interactions between plants, animals, and the environment influence the pattern and rate of successional change.Secondary succession Secondary succession follows a major disturbance, such as a fire or a flood. The stages of secondary succession are quite similar to those of primary succession; however, primary succession always begins on a barren surface, whereas secondary succession begins in environments that have soil. Also, through a process called old-field succession, farmland that has been abandoned may undergo secondary succession.In some environments, succession reaches a climax, which gives rise to a stable community dominated by a small number of prominent species. This achieved state of equilibrium, known as the climax community, is thought to result when the web of biotic interactions becomes so intricate that no other species can enter. In other environments, continual small-scale disturbances produce communities that are a diverse mix of species, and any species may become dominant. Q4) Explain the food chain and its types.Energy flow Energy flows in a single direction. Firstly, plants capture solar energy and then, transfer the food to decomposers. Organisms of different trophic levels are connected for food or energy relationship and thus form a food chain.Energy Pyramid is always upright because energy flows from one trophic level to the next trophic level and in this process, some energy is always lost as heat at each step.Nutrient Cycling Nutrient cycling is the process of storing and moving nutrient elements through the various components of the ecosystem. There are two types of Nutrient cycling, gaseous and sedimentary.For the Gaseous cycle (i.e. nitrogen, carbon), the atmosphere or hydrosphere is the reservoir whereas for the sedimentary cycle (i.e. phosphorus) Earth’s crust is the reservoir. Tropical Grasslands Temperate Grasslands Flooded Grasslands Montane Grasslands Desert Grassland Tropical GrasslandsTropical Grasslands are the ones that receive 50 cm to 130 cm rain. They have both rainy and dry days. As a result, they are warm all year round. Moreover, tropical grasslands are also called Savanna. These grasslands contain shrubs and small trees that are dry. The tropical grasslands contain quite short plants which makes it an excellent place for hunting. For example, the African savanna is one of the tropical grasslands. It can be concluded that the tropical grassland is a home for elephants, giraffes, lions, cheetahs, zebras, and other spectacular species.
Abiotic Components:
Basic inorganic compounds of an organism, habitat, or an area that are involved in the material cycles are collectively called abiotic components. They include carbon dioxide, water, nitrogen, calcium, phosphorus, etc. The amount of these inorganic substances present in an ecosystem at any given time are known as the standing state or standing quality of an ecosystem.Whereas, organic components e.g., proteins, amino acids, carbohydrates, and lipids that are synthesized by the biotic counterpart of an ecosystem make the biochemical structure of the ecosystem. The physical environment, viz. climatic and weather conditions are also included in the abiotic structure of the ecosystem. Biotic Components:
From the trophic (nutritional) point of view, an ecosystem has autotrophic (self-nourishing) and heterotrophic (other nourishing) components.(a) Autotrophic component (Producers):This component mainly comprises green plants, algae, and all photosynthetic organisms. Chemosynthetic bacteria, photosynthetic bacteria, algae, grasses, mosses, shrubs, herbs, and trees manufacture food from simple inorganic substances by fixing energy and are therefore called producers.(b) Heterotrophic component (Consumers):The members of this component cannot make their food. They consume the matter built by the producers and are therefore called consumers. They may be herbivores, carnivores, or omnivores. Herbivores are called primary consumers whereas carnivores and omnivores are called secondary consumers. Collectively we can call them macro-consumers.(c) Decomposers:Heterotrophic organisms are chiefly bacteria and fungi that breakdown the complex compounds of dead protoplasm, absorb some of the products, and release simple substances usable by the producers are called decomposers or reducers. Collectively we call them micro-consumers. Q2) Describe Producers, Decomposers, and Consumers in brief.A2) Inorganic components are synthesized into organic structures by the green plants in the habitat (primary producers) through photosynthesis and solar energy is utilized in the process. Green plants become the source of energy for renewals (herbivores) which, in turn, become a source of energy for the flesh eating-animals (carnivores). Animals of all types grow and add organic matter to their body weight and their source of energy is complex organic compounds taken as food. They consume the matter built by the producers and are therefore called consumers. They may be herbivores, carnivores, or omnivores.
All the living organisms, may they be plants or animals have a definite life span after which they die. The dead organic remains of plants and animals provide food for saprophytic microbes, such as bacteria, fungi, and many other animals. The saprobes ultimately decompose the organic structure and break the complex molecules and liberate the inorganic components into their environment.These organisms are known as decomposers. During the process of decomposition of organic molecules, the energy which keeps the inorganic components bound together in the form of organic molecules gets liberated and dissipated into the environment in the form of heat energy. Thus, in an ecosystem, energy from the sun, the input is fixed by plants and transferred to animal components.Q3) Describe Ecological succession.
A3)Ecological succession is the process by which the structure of a biological community evolves. Two types of succession i.e. primary and secondary, have been distinguished. Primary succession occurs in essentially lifeless areas—regions in which the soil is incapable of sustaining life as a result of such factors as lava flows, newly formed dunes, or rocks left from a retreating glacier. Secondary succession occurs in areas where a community that previously existed has been removed; it is classified by smaller-scale disturbances that do not remove all life and nutrients from the environment.
A4) A food chain can be defined as the transfer of energy and nutrients through a succession of organisms through a continuous and repeated process of eating and being eaten. In the food chain, the initial link is a green plant or producer which produces chemical energy available to consumers. For example, marsh grass is consumed by grasshopper, the grasshopper is consumed by a bird and that bird is consumed by a hawk.
Thus, a food chain is formed which can be written as follows:Marsh grass → grasshopper → bird → hawkThe food chain in any ecosystem runs directly in which green plants are eaten by herbivores, herbivores are eaten by carnivores, and carnivores are eaten by top carnivores. Man forms the terrestrial links of many food chains.Food chains are of three types:1. Grazing food chain2. Parasitic food chain3. Saprophytic or detritus food chain1. Grazing food chain:The grazing food chain starts from green plants and autotrophs it goes from herbivores (primary consumers) to primary carnivores (secondary consumers) and then to secondary carnivores (tertiary consumers) and so on. The gross production of a green plant in an ecosystem may meet three fates—it may get oxidized in respiration, it may be eaten by herbivorous animals and after the death and decay of producers it may be consumed by decomposers and converters and finally released into the environment. In herbivores, the assimilated food can be stored in the form of carbohydrates, proteins, and fats, and later transformed into much more complex organic molecules.The energy for these transformations is supplied through respiration. As in autotrophs, the energy in herbivores also meets three routes respiration, the decay of organic matter by microbes, and consumption by the carnivores. Similarly, when the secondary carnivores or tertiary consumers eat primary carnivores, the total energy digested by primary carnivores or gross tertiary production follows the same course, and its positioning in the sequence of respiration, decay, and further consumption by other carnivores is entirely similar to that of herbivores.2. Parasitic food chain:It goes from large organisms to smaller ones without outright killing as in the case of a predator.3. Detritus food chain:The dead organic remains including metabolic wastes and exudates derived from the grazing food chain are generally termed detritus. The energy contained in detritus is not lost in the ecosystem as a whole, rather it serves as a source of energy for a group of organisms called detritivores that are separate from the grazing food chain. The food chain so formed is called the detritus food chain.In some ecosystems, more energy flows through the detritus food chain than through the grazing food chain. In the detritus food chain, the energy flow remains as a continuous passage rather than as a stepwise flow between discrete entities. The organisms in the detritus food chain are many and include algae, fungi, bacteria, slime molds, actinomycetes, protozoa, etc. Detritus organisms ingest pieces of partially decomposed organic matter, digest them partially and after extracting some of the chemical energy in the food to run their metabolism, excrete the remainder in the form of simpler organic molecules.Q5) What is an ecological pyramid?A5) The trophic structure of an ecosystem can be indicated using an ecological pyramid. At every step in the food chain, a considerable fraction of the potential energy is lost in the form of heat. As a result, organisms in each trophic level pass on lesser energy to the next trophic level than they receive. This limits the number of steps in any food chain to 4 or 5. The longer the food chain the lesser energy is available for final members. Because of this tapering off of available energy in the food chain, a pyramid is formed that is known as an ecological pyramid. The higher the steps in the ecological pyramid the lower will be the number of individuals and the larger their size.
There are different types of ecological pyramids. In each ecological pyramid, the producer level forms the base and successive levels make up the apex. Three types of pyramidal relations may be found among the organisms at different levels in the ecosystem.These are as follows:1. Pyramid of numbers,2. Pyramid of biomass (the weight of living organisms is known as biomass), and3. Pyramid of energy.1. Pyramid of numbers:It depicts the numbers of individuals in producers and different orders of consumers in an ecosystem. The base of the pyramid is represented by producers which are the most abundant. In the sequence of consumers, the number of organisms goes on decreasing rapidly until there are a few carnivores.The pyramid of numbers of an ecosystem shows that the producers are consumed in large numbers by smaller numbers of primary consumers. These primary consumers are eaten by a relatively smaller number of secondary consumers and these secondary consumers, in turn, are consumed by only a few tertiary consumers.This type of pyramid can be best shown by way of an example of Lake Ecosystem. In this type of pyramid, the base trophic level is occupied by producer elements—algae, diatoms, and other hydrophytes which are most abundant. At the second trophic level are the herbivores or zooplanktons which are lesser in number than producers.The third trophic level is occupied by carnivores which are still smaller in number than the herbivores and the top is occupied by a few top carnivores. Thus, in the ecological pyramid of numbers, there is a relative reduction in the number of organisms and an increase in the size of the body from the base to the apex of the pyramid. In a parasitic food chain starting from the tree, the pyramid of numbers will be inverted.2. Pyramid of the biomass of organisms:The living weights or biomass of the members of the food chain present at any one time form the pyramid of the biomass of organisms. This shows the total bulk of organisms or fixed energy present at one time by weight or other means of measuring materials. The pyramid of biomass indicates the decrease of biomass in each tropic level from base to apex, e.g., the total biomass of producers is more than the total biomass of the herbivores.Likewise, the total biomass of secondary consumers will be lesser than that of herbivores and so on. Since some energy and material are lost in each successive link, the total mass supported at each level is cut short by the rate at which the energy is being stored in the level below. This usually gives a sloping pyramid for most of the communities in terrestrial and shallow-water ecosystems. The pyramid of biomass in a pond ecosystem will be inverted as shown in the figure below.3. Pyramid of energy:This depicts not only the amount of total energy utilized by the organisms at each trophic level of the food chain but more importantly, the actual role of various organisms in the transfer of energy. At the producer level, the total energy will be much more than the energy at the successive higher trophic level.Some producer organisms may have small biomass but the total energy they assimilate and pass on to consumers may be greater than that of organisms with much larger biomass. Higher trophic levels are more efficient in energy utilization but a lot of heat is lost in energy transfer. Energy loss by respiration also progressively increases from lower to higher trophic states.Q6) State the components of the forest ecosystem.A6) Components of a Forest EcosystemThe components of a forest ecosystem are as follows: Productivity
The basic requirement for any ecosystem to function smoothly and to sustain is the constant input of solar energy. Plants are also the producers in a forest ecosystem.In a forest ecosystem, productivity is of two types: primary and secondary. Primary productivity means the rate of capture of solar energy or biomass production per unit area over some time by the plants during photosynthesis.It is further divided into Gross Primary Productivity (GPP) and Net Primary Productivity (NPP). GPP of an ecosystem can be defined as the rate of capture of solar energy or the total production of biomass. However, plants also utilize a significant amount of GPP in respiration.Thus, NPP is the amount of biomass left after the utilization by plants or the producers. We can hence say that NPP is the amount that is available for consumption to herbivores and decomposers. Secondary productivity means the rate of absorption of food energy by the consumers. Decomposition
Decomposition is an extremely oxygen-requiring process. In the process of decomposition, the complex organic compounds of detritus are converted into inorganic substances such as carbon dioxide, water, and nutrients by the decomposers.Detritus is the remains of the dead plant such as leaves, bark, flowers, and also the dead remains of the animals including their faecal matter. The steps involved in the process of decomposition are fragmentation, leaching, catabolism, humification, and mineralization.In the process of fragmentation, detritivores break down the detritus into smaller particles. In the process of leaching, water-soluble inorganic nutrients descend into the soil and settle as unavailable salts.Under the process of catabolism, bacterial and fungal enzymes reduce detritus into simpler inorganic substances. Humification and mineralization processes occur during the decomposition of soil and not detritus.The process of humification leads to the accumulation of humus which decomposes at a very slow rate. In the process of mineralization, the humus gets further degraded by microbes and inorganic nutrients are released.Q7) Describe the types and structure of the grassland ecosystem.
A7) Grassland ecosystem has five types of grasslands: Temperate Grasslands
Temperate grasslands receive rainfall of the range 25 cm and 75 cm. Furthermore, the climate in the temperate grasslands makes it both dormant and growing. Moreover, these grasslands suffer extreme climates. In the cold season, the temperature can reach up to 0 degrees Fahrenheit. While in the summer season it may go up to 90 degrees in some regions. The precipitation in these grasslands is mostly in the form of dew and snow. Some vegetation that grows here are, cacti, sagebrush, perennial grasses, buffalo grass clovers, and wild indigos, etc. Flooded GrasslandsThe flooded grasslands are having water all year-round. These grasslands have numerous plants that grow in water. Various water birds migrate to these areas while some are residents of them. The Everglades is the world’s largest flooded grasslands. It features various types of birds, fish, mammals, reptiles, seed-bearing plants, amphibians, etc. Montane Grasslands
The word Montane means ‘high altitude’. As per the name, these are the grasslands that are high altitude shrublands. These are called high altitude because they are above the tree line level of the ground. The plants found here have a rosette structure, abundant pilosity, and waxy surfaces. The northern Andes contain this type of habitat. Desert Grasslands
The desert grasslands are the type of grasslands that separates the true desert of the lowlands and the montane grasslands. These grasslands receive very low precipitation. Because of this, these are the hottest and the driest grasslands. These grasslands are mostly scattered as they are dependent on the areas of rainfall. Since the precipitation varies through regions. Therefore, the vegetation of the grasslands also varies. Moreover, various types of animals are present in these grasslands. Structure of Grassland ecosystem.The structure of the grassland ecosystem consists of biotic and abiotic components. The biotic components are three; producer organisms, consumers, and decomposers. The producer organisms are mainly eating grasses, though a few herbs and shrubs also make up for primary production in the biomass. The consumers in the ecosystem are mainly of three types: the primary consumers which refer to the herbivores that feed on the grasses, for example, the cows and goats, secondary consumers; the carnivores that take in primary consumers for example frogs, snakes, and jackals. There are also the tertiary consumers like the hawks that eat the secondary consumers. The third type of biotic component is the decomposers which include many saprotrophic microorganisms, for example, bacteria, fungi, and Actinomycetes. They attract the decayed bodies of organisms which aid in the process of decomposition, and the nutrients are given out for reuse by the producers. There are also the abiotic components in the ecosystem which are made up of the organic and inorganic compounds which are in the soil and the aerial environment.Q8) Explain the importance of the desert ecosystem.A8) The desert biome is very important to this earth. Deserts are found on every single continent, and though they lack water, they play an essential role in helping animals, humans, and the environment.
1. Flora & FaunaDeserts are home to a variety of unique plants and animals that have adapted to their harsh habitats. They are home to various livestock such as camels, goats, and antelope that provide food and livelihood for people. Desert shrubs and trees that produce fruit such as dates, and figs, and olives are an important food source in North Africa and the Middle East.Besides adding to the Earth’s biodiversity, many of these plants and animals benefit humans. Domesticated camels in the deserts of Asia and North Africa have been reliable pack animals for thousands of years. If deserts disappear, many insects and animal species will also disappear. Many biotic factors depend on deserts for food, water, and shelter.2. Mineral ResourcesThere are 15 types of mineral deposits on our planet, and 13 of them are found in deserts. Some important minerals are formed in the dry condition of deserts. Gypsum, borates, nitrates, potassium, and other salts build up in deserts when water carrying these minerals evaporates. The extraction of important minerals from desert regions has become easier due to less vegetation in the area.According to United Nations statistics, over 50% of world copper comes from deserts in Mexico, Australia, and Chile. Other minerals and metals such as bauxite, gold, and diamonds are found in large quantities in the deserts of China, the United States, and Namibia. Desert regions also hold 75% of known oil reserves in the world.3. Carbon SinksScientists discovered that cyanobacteria living in the sands of the Kalahari Desert of Botswana help gather and store carbon dioxide from the air.These drought-resistant bacteria can fix atmospheric carbon dioxide, and together they add large quantities of organic matter to the nutrient-deficient sand. Since carbon dioxide is one of the prime causes of global warming, these desert sands may play a critical role in preventing additional carbon dioxide from entering the atmosphere.4. Archaeological DiscoveriesArid conditions are ideal for preserving human artifacts and remains. Present-day archaeologists came to know about ancient civilizations because of the mummified human remains found in countries like Peru, China, and Egypt. Discoveries like these help in shaping the modern understanding of how our societies first formed.5. Leisure and TourismDeserts attract millions of visitors every year. The deserts of the Middle East and North Africa have the Great Pyramids of Giza in Egypt. Jordan’s city of Petra, Carthage, and others are places that show well-preserved archaeological ruins of the past.The Anasazi houses at Mesa Verde are an incredible sight, as is the Casa Grande monument in Arizona, built by the Hohokam Culture. In South America, there are many sites and artifacts recovered from the Atacama.6. Bio-ProspectingDesert plants have adapted such special properties that help them survive in extremely harsh desert climates. According to a UN report on the global outlook of deserts, a recent survey of plants in Israel’s Negev desert found plants that could help fight malaria.Q9) State the types of the aquatic ecosystem and its functions.
A9) Different types of aquatic ecosystems are as follows:
1. Freshwater Ecosystem:
These cover only a small portion of the earth which is nearly 0.8 percent. Freshwater means lakes, ponds, rivers and streams, wetlands, swamps, bogs, and temporary pools.
2. Lotic Ecosystems:
These mainly refer to the rapidly flowing waters that move in a single direction including the rivers and streams. These environments are comprised of numerous species such as beetles, mayflies, stoneflies, and several species of fishes including trout, eel, minnow, etc.
3. Lentic Ecosystems:
They include all standing water habitats. Lakes and ponds are the primary examples of the Lentic Ecosystem. These ecosystems contain species such as algae, crabs, shrimps, and amphibians such as frogs and salamanders.
4. Wetlands:
Wetlands are marshy areas and are sometimes covered in water that supports a wide variety of plants and animals. Swamps, marshes, bogs, black spruce, and water lilies are the main examples of the plant species. The animal life of this ecosystem consists of dragonflies, damselflies, and various birds and fishes.
5. Marine Aquatic Ecosystem:
The marine ecosystem covers the largest surface on the earth. Two-thirds of the earth is covered by water which includes oceans, seas, intertidal zone, reefs, seabed, etc. Each life form is unique and native to its habitat.
6. Ocean Ecosystems:
Our earth is having five major oceans. Moreover, these oceans are like a home to more than five lakhs of aquatic species. Some species of this ecosystem include shellfish, Shark, Tube Worms, Crab Small, and large ocean fishes.
7. Coastal Systems:
These are the open systems of land and water that are combined to form the coastal ecosystems. A wide variety of species of aquatic plants and algae live at the bottom of it. The diverse fauna consists of crabs, fish, insects, lobsters, snails, etc.
Functions of an aquatic ecosystem are:Aquatic ecosystems perform many important environmental functions. For example, they recycle nutrients, perform water purification, attenuate floods, recharge groundwater and provide habitats for wildlife. Aquatic ecosystems are also helpful for human recreation, and are very important to the tourism industry, especially in coastal regions. The health of an aquatic ecosystem is degraded when the ecosystem's ability to absorb stress has been exceeded. A stress on an aquatic ecosystem can be a result of physical, chemical, or biological alterations to the environment. Physical alterations may include changes in water temperature, water flow, and light availability. Chemical alterations include changes in the loading rates of bio-stimulatory nutrients, oxygen consuming materials, and toxins. Biological alterations include over-harvesting of commercial species and the introduction of exotic species. Human populations can impose excessive stresses on aquatic ecosystems. There are many examples of excessive stress with negative consequences.
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