Title Med-RM_Bot_SP-4_Ch-18_Organisms and Populations.pdf ✅

Chapter Contents Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Chapter 18 Organisms and Populations Levels of Organisation Organism and Its Environment Populations Ecology deals with the study of interactions and interrelationships between organisms and their environment. LEVELS OF ORGANISATION The various levels of ecological organisation are organism, population, community, ecosystem, landscape, biome and biosphere. 1. Organisms They are basic unit of study in ecology. At the level of organism, we intend to understand the form, physiology, behaviour, distribution and adaptations in relation to the environmental conditions. 2. Population It is a grouping of individuals of the same species inhabiting a given area. 3. Biological community It is an assemblage of population of different species present in an area which show interdependence and interaction like competition, predation, host-parasite interaction, amensalism etc. 4. Ecosystem It is composed of a biological community, integrated with its physical environment through the exchange of energy and recycling of the nutrients. 5. Landscape A unit of land with a natural boundary having mosaic of patches which generally represent different ecosystems. 6. Biome A large regional unit characterised by a major vegetation type and associated fauna found in a specific climatic zone. 7. Biosphere It is life supporting zone which comprises all the earth’s terrestrial and aquatic biomes. Ecology is basically concerned with four levels of biological organisation - organisms, population, communities and biomes.
2 Organisms and Populations NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Note : 1. Term ecology was first used by Reiter in 1868. 2. Ernst Haeckel (1886) first correctly defined ecology as the science dealing with reciprocal relationship of organisms and the external world. 3. Prof. R. Mishra is known as father of ecology in India. Warming is known as father of plant ecology. 4. E.P. Odum – defined it as the “study of structure and function of nature”. ORGANISM AND ITS ENVIRONMENT Ecology at the organismic level is essentially a physiological aspect. It tries to understand how different organisms are adapted to surrounding environment in terms of their survival and reproduction. The rotation of earth around sun and the tilt of its axis cause annual variation in the intensity and duration of temperature. It results in formation of different seasons like summer, winter, spring and autumn. These variations in temperature together with annual variation in precipitation (includes both rainfall and snow) account for the formation of major biomes. Rainfall, temperature range, nature of soil, barriers, latitude and altitude determine the nature and extent of biomes. Some important major biomes are as follows. Terrestrial Biomes 1. Tundra 2. Taiga (coniferous forest) 3. Temperate forest 4. Grasslands 5. Desert 6. Tropical rain forest. (i) Temperate grassland (ii) Tropical savanna grassland (grass cover with scattered trees) Fig.: Biome distribution w.r.t. annual temperature and precipitation Mean annual precipitation (cm) Arctic and Alpine tundra Coniferous forest Temperate forest Tropical forest Desert Grassland 30 25 20 15 10 5 0 –5 –10 –15 50 100 150 200 250 300 350 400 450 Mean annual temperature (oC)
NEET Organisms and Populations 3 Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Regional and local variations within each biome lead to the formation of wide variety of habitats. Organisms can exist in both favourable as wells in the extreme and harsh habitats such as scorching Rajasthan desert, rain soaked Meghalaya forests, deep ocean trenches, torrential streams, permafrost (snow laden) polar region, high mountain tops, boiling thermal springs and stinking compost pits. Human intestine is also a unique habitat of several species of microbes. Variations in mean annual temperature and precipitation leads to the formation of some important biomes in India. The comparative study of major Indian biomes is as follows: Table : Major biomes of India and their features S. No. Type of Biome Mean Annual temperature (oC) Mean annual rainfall (mm) Important vegetation 1. Tropical rain forest 23-27 2000-3500 Dipterocarpus, Hopea 2. Tropical deciduous forest 22-32 900-1600 Sal, Teak, Tendu, Chiraunji, Khair 3. Temperate broad-leaf forest 6-20 1000-2500 Oak (Quercus) 4. Temperate needle leaf forest 6-15 500-1700 Pine, Deodar, Cypress, Spruce, Silver fir (a) (b) (c) (d) Fig.: Major Biomes of India: (a) Tropical Rain Forest, (b) Deciduous forest; (c) Desert, (d) Sea Coast
4 Organisms and Populations NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Abiotic environment includes three categories of factors– climatic, edaphic and topographic. Climatic factors are light, temperature, water and wind. Edaphic factors are factors related to soil. Topographic factors are physical factors related to slope, altitude and others concerned with surface behaviour of earth. Key abiotic factors Temperature Light Soil Water Fig.: Key abiotic factors  Habitat of an organism includes biotic components also, such as variety of pathogens, parasites, predators and competitors of an individual organism. All these interact constantly with the organism.  Ecological niche (Concept given by J. Grinnel) Each organism represents, the range of conditions that it can tolerate, the resources it utilises and its functional role in ecological system. Each species has a distinct niche and no two species are believed to occupy exactly the same niche. Over a period of time, the organisms evolved adaptations to optimize its survival and reproduction in its habitat through natural selection.  Ecological equivalents : Organisms that occupy the same or similar ecological niches in different geographical regions are known as ecological equivalents. e.g. Owl and cat. Major Abiotic Factors Temperature : Temperature is the most ecologically relevant environmental factor. Temperature plays an important role in both latitudinal and altitudinal distribution of organisms. For example, mango a tropical and subtropical tree plant is not found in temperate countries like Canada and Germany. Similarly, snow leopards (polar animals) are not found in Kerala forests and tuna fish (a bony tropical fish) is not found beyond tropical latitudes in ocean. Temperature, significantly affects the enzyme kinetics and basal metabolism as well as activity and other physiological functions of the organism. Types of Organism on the basis of temperature (i) Based upon thermal tolerance, organisms are classified into two categories: Such organisms live in areas where the temperature is uniform throughout the year. These organisms cannot tolerate large temperature variations and thus, restricted to narrow range of temperatures. Vast majority of organisms belong to this category. e.g., Abies. polar bears, lizards, A few organisms can tolerate and thrive in a wide range of temperatures. They are called as eurythermal. Such organisms can tolerate large changes in temperature. e.g., most of the mammals and birds. Stenothermal Eurythermal