Title Med-RM_Bot_SP-4_Ch-19_Ecosystem.pdf ✅

Chapter Contents Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Types of Ecosystem Ecosystem - Components Ecosystem - Structure Ecosystem - Function Ecological Pyramids Ecological Succession Nutrient Cycle Ecosystem Services Wide range of living organisms are present on earth surface. All living organisms such as plants, animals and microorganisms interact among themselves and also with the surrounding physical environment and maintains a balance in nature. This forms a self- sustaining or functional unit of the living world called as ecosystem. Thus, an ecosystem consists of interaction of biotic component comprising living organisms and abiotic components comprising physical factors like temperature, rainfall, wind, soil and minerals. TYPES OF ECOSYSTEM Ecosystem varies greatly in size from a small pond to a large forest or a sea. Many ecologists regard the entire biosphere as a global ecosystem as a composite of all local ecosystems on earth. Since this system is too much big and complex to be studied at one time, so to make the study easier, it is broadly divided into two basic categories : (i) Terrestrial Ecosystem : It occurs over land e.g., forest, grassland, desert. (ii) Aquatic Ecosystem : It occurs in water bodies e.g., pond, lake, river (fresh water), wet land, sea, estuaries (salt water). Similarly, w.r.t. human interference the ecosystems are of two types: (i) Natural ecosystem : It develops in nature without human support or interference e.g., forests, marine ecosystem. (ii) Anthropogenic ecosystem or man-made ecosystem : It is the one which is created and maintained by human beings e.g., crop fields, garden, aquarium. Agroecosystem or agriculture is the largest man- made ecosystem. Characteristics of anthropogenic ecosystem : (i) Do not possess self regulatory mechanism (ii) Have little diversity (iii) Simple food chain (iv) High productivity (v) Little cycling of nutrients Chapter 19 Ecosystem
46 Ecosystem NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Note : Tansley : Coined the term ecosystem and defined it as the sum total of interactions between living (biotic) and non living (abiotic) components which is capable of independent existence. ECOSYSTEM - COMPONENTS An ecosystem is made up of two components i.e., abiotic and biotic. I. Abiotic Components The non-living factors or the physical environmental factors prevailing in an ecosystem constitute the abiotic components. They are mainly of three types i.e., climatic, edaphic and topographic factors. II. Biotic Components All living organisms i.e., plants, animals and microorganisms that are present in environment constitute the biotic components of the ecosystem. On the basis of their role in the ecosystem, these can be classified into three main groups: (i) Producers : They are green photosynthetic plants. So, they are called autotrophs. In terrestrial ecosystem, major producers are herbaceous and woody plants. In aquatic ecosystem, chief producers are phytoplanktons, algae and the floating, submerged and marginal plants found at the edges. Producers are also known as “converters” or “transducers” because they convert solar energy into chemical energy stored in the bonds of sugars. (ii) Consumers : They are heterotrophs. Consumers are of following types : (a) Primary Consumers (PC) or First Order Consumers : These animals directly feed on producers. They are also called herbivores or key industry animals. (Convert plant matter into animal matter) Terrestrial ecosystem : Common herbivores are grasshopper, cow and deer. Aquatic ecosystem : Common herbivores are molluscs, tadpole and mosquito larvae. (b) Secondary Consumers (SC) or Second Order Consumers or Primary Carnivores : They are animals which feed on herbivores. Terrestrial ecosystem : Toad, spiders, lizards, centipedes and insectivorous birds. Aquatic ecosystem : Hydra, frog and some fishes. (c) Tertiary Consumers (TC) or Third Order Consumers or Secondary Carnivores : Carnivores which feed upon secondary consumers e.g., large fishes (aquatic ecosystem), snake (terrestrial ecosystem). There may be quarternary or fourth order consumers which prey upon secondary carnivores. (d) Top Carnivores: The carnivores which are not eaten by others are called top carnivores. They may belong to the category of primary, secondary, tertiary carnivores. e.g., tiger, lion, panthers and falcon,peacock. (iii) Decomposers :They are saprophytic microorganisms. They bring about cyclic exchange of materials between biotic community and the environment. They are thus, very essential components of an ecosystem. They are also called reducers as they are capable of degrading the dead organisms. These are the fungi, bacteria and flagellates especially abundant in the bottom of the pond. Decomposition involves the following conversions : Complex organic substances  Simple organic substances  Inorganic compounds
NEET Ecosystem 47 Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Functions of decomposers in ecosystem : 1. They are natural scavengers as they reduce organic remains of earth. 2. Replenish the soil naturally with minerals that are essential for growth of plants and hence, maintenance of ecosystem. Some workers differentiated few other categories of living beings amongst the biotic components of an ecosystem. They are scavengers, detrivores and parasites. Parasites belong to diverse groups, e.g., bacteria, fungi, protozoans, worms etc. Detrivores are animals which feed on detritus e.g., termites, earthworm etc. They are helpful in quick disposal of the dead bodies. Scavengers are animals that feed on dead or injured animals and they clean the earth of organic garbages e.g., carrion beetles, marabou storks, crow and vultures (full-time scavengers). Ecosystem Components Biotic Abiotic Producers (Autotrophs) Consumers (Heterotrophs) Decomposers (Saprotrophs) Climatic factors Topographic factors Edaphic factors Primary Secondary Tertiary Top ECOSYSTEM - STRUCTURE Interaction of biotic and abiotic components result in a physical structure that is characteristic for each type of ecosystem. Important structural features include : (i) Species Composition : It is the identification and enumeration of plant and animal species of an ecosystem. For example, tropical rain forest is dense with amazing number of biological species. On the other hand, vegetation is sparse in the desert ecosystem. (ii) Stratification : Vertical distribution of different species occupying different levels. It is the structure as recognizable pattern in spatial arrangement of the members of the communities. For example, in a forest following vertical subdivisions are present. (a) Top layer – Trees. (b) Second layer – Shrubs. (c) Bottom layer – Grasses and herbs. ECOSYSTEM - FUNCTION Ecosystem possesses a natural tendency to persist. This is made possible by a variety of functions (activities undertaken to ensure persistence) performed by the structural components. The key functional aspects of the ecosystem are: (I) Productivity (II) Decomposition (III) Energy flow (IV) Nutrient cycling
48 Ecosystem NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 (I) Productivity It is the rate of biomass production. Productivity in ecosystem is of two types – Primary and Secondary productivity. 1. Most productive ecosystem are coral reefs, tropical rain forest, sugarcane field. 2. Least productive ecosystem – Desert and deep sea. (i) Primary Productivity : It is the rate at which biomass or organic matter is produced by plants or producers during photosynthesis per unit area over a time period or it refers to rate at which sunlight is captured by producers for the synthesis of energy-rich organic compounds through photosynthesis. It is expressed in terms of weight as (gm m–2)yr–1 or energy as (Kcalm–2)yr–1 to compare the productivity of different ecosystems. It can be further divided into two categories : (a) Gross Primary Productivity (GPP) : Rate of production or synthesis of organic matter by producers during photosynthesis per unit time and area. Energy-captured process is operating in the green tissues; these as well as other tissues are consuming photosynthates in respiration. So, considerable amount of GPP is utilised by plants in respiration. (b) Net Primary Productivity (NPP) : Gross primary productivity minus respiratory losses (R). So you can say, it is rate of organic matter build up or stored by producers in excess of respiratory utilization per unit time and area. NPP = GPP – R Net primary productivity is the available biomass for the consumption to heterotrophs i.e., both herbivores and decomposers. Factors affecting primary productivity : Several biotic and abiotic factors given below affects magnitude of primary productivity. (i) Photosynthetic capacity of producers which means the ability to utilise incident solar radiation to raise gross primary productivity. (ii) Solar radiations available (iii) Temperature (iv) Soil moisture (v) Availability of nutrients Productivity of biosphere : Annual NPP of whole biosphere is approximately 170 billion tons (dry weight) of organic matter. Of this, despite occupying about 70% of the surface, the productivity of oceans are only 55 billion tons and for terrestrial ecosystem is 115 billion tons. Reasons for the low productivity of oceans : In deep marine habitats two main limiting factors are there. (i) Light : It decreases with depth. (ii) Nutrients : Most limiting nutrient of marine ecosystem is nitrogen. (ii) Secondary productivity : It is the rate of formation of new organic matter by consumers. (iii) Community productivity : It is the rate of net synthesis and build up of organic matter by a community per unit time and area.