UNIT 17 ECOSYSTEM AND FUNCTION - I Structure 17.1 Introduction Objectives 17.2 Ecosystem 17.3 Component of Ecosystem Abiotic Components Biotic Components Trophic Levels Food Chain Food Web Bioaccumulat~onand B~omagnification 17.4 Pyramids Pyramid of Numbers Pyra~n~dof Biomass Pyramid of'Energy 17.5 Energy of Ecosystem Flow of Energy in An Ecosystem Law of Thermodynamics 17.6 I'roductivity Primary Production Secondary Production 17.7 Homeostasis System Feedback Mechanism Ecosystem Homeostasis 1 7.8 Community and Ecological Succession Succession in Terrestrial Community Succession in Aquatic Habitat General Characteristic of Succession 1 7.9 Ecosystem and Human Use 1 7.1 0 Ecosystems and Human Intervention 1 7.1 1 Summary 1 7.12 Terminal Questions 17.1 INTRODUCTION We all live in a community, consisting of plants, animals, microorganisms and deconiposers that interact with one another and with their environments and are interdependent on one another for survival. The biotic components consist of producers and consumers. When sitting on dinner table you must be enjoying your non-vegetarian dish, this dish, is a part of a food chain that feed on one another. The abiotic components contribute substances needed for the ecosystem to function. Ecosystem is maintained through energy flow, the energy flow is unidirectional from sun to producers. Ecosystems are therefore systems in which there is a regulated transfer of energy and an orderly, controlled cycling of nutrients. An ecosystem self regulates or self maintains itself through homeostatis. They, over a period of time, with changing climate, slowly have modified into new ecosystems through a process called succession. In recent times human beings have negatively intervened in the working of ecosystem through introducing new species, predator-control practices, habitat destruction and pesticide use (biomagnifications) all of which have had unanticipated changes in ecosystem. Objectives After studying this unit you will be able to: identify the abiotic and biotic environmental factors, appreciate the relationship of organisms in food chain and food web, idcntify the tropliic levels occupied by herbivores and carnivores, and Function - recognise the value of using a pyramid of number, pyramid of biomass or pyramid of energy, explain the laws of thermodynamics, recognise-the importance of primary productivity and secondary productive in an ecosysteln, describe the process of succession in terrestrial and aquatic ecosystem, describe various examples of human interventions towards destruction of natural ecosystems. 17.2 ECOSYSTEM Each biome is constituted bv several ecosvstenls. For exam~le,~~. the desert.~~ - ~ - ~ biome- .- --.. of - - ~ I J -~ Rajasthan is cllaracterised by arid conditions, sandy terrain, cacti and succulent plants Animals found there are lizards, snakes, camels. A subdivision of biome such as a pond is called an ecological system or ecosystem. The word ecosystem; \was I The vario~~skinds of organisms that inhabit an ecosystem form its populations. The coined by Prof. Arthur Tansley in 1935, l'he term, 'population' has many uses and meanings in other fields of study. In ecology, 'a prefix 'eco' means population is a group of potentially interbreeding individuals that occur together environment. in space and time'. The individuals comprising a population are members of the same species. I Popi~latiollsof plants and animals in the ecosystem do not function independently of each other. They are always influencing each other and organising themselves into communities and have fcrnctional relationship with their external environment. 1 An ecosystem is defined as, any unit (a biosystem) that includes all the organisms that function toeether (the biotic community) in a given area, interacting with the u ", - - physical environment (abiotic component) so that flow of energy leads to clearly defined biotic structures and cycling of materials between living and non-living parts and which is self regulatory based on feed-back information about the population, and the limiting factors which control the living and non-living components. (Fig.17.1) Abnosphere Soil and water Carbon dioxide1 ~utrink and methane &Carbon diox~de Fig.17.1: Simplified biosphere. The different organisms of our biosphere cooperate in similar ways to create a functioning ecosystem. The definition of ecosystem as you can see involves the interaction between living and non-living components of an ecosystem and input, transfer, storage and output of energy as well as cycling of essential materials through the system. Each of these 1 Ecology and Environment processes is energy dependent. As a result of these complex interactions, the ecosystem has to adjust to these changes to attain a state of equilibrium. Figure 17.2, illustrates this beautifully. Ecosystems differ greatly in composition, in the number and kinds of species, in the kinds and relative proportions of non-biological constituents and in the degree of variations in time and space. A Radiant . WY*".."".""'.'."'. I Fig. 17.2: Schematic representation of an ecosystem. The dotted lines represent the boundary of the system. The three major components are the producers, the consumers, and the abiotic elements: inactive or dead organic matter, the soil matrix, nutrients in solution in aquatic ecosystems, sediments, and so on. The arrows indicate interactions within the system and with the environment. 17.3 COMPONENTS OF ECOSYSTEM Any complete definition of an ecosystem includes the biotic as well as the abiotic components and the interaction between the two. I 17.3.1 Abiotic Components One of the important components of the ecosystem is abiotic or non-living components about which you have already read in section 16.2 (Refer to table 16.1 as well). h he physical or abiotic components are the non-living parts of the earth such as soil, water, air, and light energy etc. It also involves a large number of chemicals like oxygen, nitrogen etc. and chemical as well as physical processes including volcanoes, earthaiakes. floods. forest fires. climates. and weather conditions. There are numerous chemical processes, but the most important ones include the carbon, nitrogen and phosphorous cycles. These physical and chemical processes are the result of the physical characteristics of the earth: air, moisture, light and heat, and the various chemical reactions. While each of these abiotic factors may be studied by itself, each of these factors influences and are in turn is influenced by all the other factors. Abiotic factors are usually the most important determinants of where and how well an organism exists in its environment. Although these factors interact with each other, usually there is one single factor which serves to limits the range of an organism. That single factor is called the limiting factor. Let us now discuss some of the important abiotic factors: i) Light: Light energy is necessary for green plants to cany on photosynthesis. All animals are directly or indirectly dependent on the food substance produced by green plants. The intensity, duration and wavelength (color) of light are Ecosystem - structure important factors that regulate the life activities of many living things. Light and Function - 1 from the sun (solar energy) is the ultimate source of energy for all living things. The availability of light energy differs greatly on different parts of the earth. Precipitation: Precipitation in the form of fog, rain, sleet, snow, and hail is one of the most important abiotic factors. Most organisms depend on some form of precipitation, either directly or indirectly, from underground. The amount of precipitation differs, depending where on earth you are. iii) Humidity and Water: Moisture in the air is very necessary for many plants and animals to function properly. Some animals are, active only at night when the humidity is higher. Aquatic habitats are subject to changes in chemical and gas content and to fluctuations of depth. Water holes in the Everglades of Florida and the Savanna of Africa are essential for the existence of native wildlife. Temperature: Many living things cany on their life activities at temperatures between 30 1" F and 185' F. Some organisms are able to exist at much lower temperatures. The daily and seasonal temperature changes often act as limiting factors and determine the number and kind of organisms present in a region. Temperature patterns vary with latitudes and altitudes of the earth. Substrate: This is defined as the base of material on which an organism lives. The type of soil, for example, is a limiting factor for the vegetation, which in turn, may be a determinant for the animal life capable of living in the habitat. 'The type of soil will determine such factors as pH as also the amount and type of minerals present. vi) Atmospheric gases: Oxygen and carbon dioxide are generally not limiting factors for terrestrial organisms. These two gases are abundant in our atmosphere. The atmospheric gases can be limiting factors for aquatic organisms. vii) Altitude: Precipitation and temperature both vary with elevation. Usually precipitation increases with elevation although at extreme elevations it may decrease. Temperature usually decreases 2-3 degrees per thousand feet. viii) Latitude: As one moves north or south of the equator, the angle of the sun generally decreases, which results in a decrease in the average temperature. ix) Topography: Landforms like mountains, valleys, basins, cliffs, etc. may encourage, restrict or isolate organisms. x) Seasonal changes: Because of the tilt of the earth on its axis, the angle of solar radiation varies during the year as one travels from the equator. It produces pronounced changes in the weather during the year, giving rise to seasons like winter, spring, summer, and autumn. xi) Weather: is the combination of temperature, humidity, precipitation, wind, cloudiness and other atmospheric conditions at a specific place and time and has profound effect on organism. xii) Climate: is the long-term average pattern of weather and influences the vegetation and organisms of a place. It is in this abiotic background that biotic organisms i.e.