ECOSYSTEM INTRODUCTION • Ecosystem is the smallest structural and functional unit of nature or environment where living organisms interact among themselves and also with the surrounding physical environment. • Ecosystem may be large or small. A single drop of water may be an ecosystem. • Ecosystem may be temporary or permanent. TYPES OF ECOSYSTEM • An ecosystem may be natural or artificial. • Natural ecosystem is divided into two basic categories – 1. Terrestrial ecosystem : E.g., forest, grassland, tree, desert ecosystem. 2. Aquatic ecosystem : Aquatic ecosystem is again of two types: a) Lentic ecosystem : E.g., Stagnant fresh water, lake, pond, swamp. b) Lotic ecosystem : Running freshwater ecosystem. E.g., river. • Artificial ecosystem : These are man made ecosystem. E.g., cropland, gardens etc. • On the basis of size, types of ecosystem are :- a) Mega ecosystem – Ocean/Sea b) Macroecosystem – Forest c) Microecosystem – Pond d) Nanoecosystem – Drop of water COMPONENTS OF ECOSYSTEM An ecosystem is composed of two components – • Biotic component • Abiotic component BIOTIC COMPONENTS • Biotic component is made up of many different inter dependent population, e.g., plants, animals, microbes, etc. • Types of biotic component are – a. Producers b. Consumers & c. Decomposers PRODUCERS • All the autotrophs of an ecosystem are called producers. • The green plants are the main producers. • Producers are generally chlorophyll bearing organisms which produce their own food by the process of photosynthesis, in which producers absorb solar energy and convert it into chemical energy. • So producers are also called transducers or converters. E.g., yellow green algae, algal protist etc. • Energy enters into the ecosystem through the producers. • The solar energy is the only ultimate source of energy in the ecosystem. This energy is available for the remaining living organisms. • Other examples of producers are – a) Chemoautotrophs : Iron bacteria, sulphur bacteria, nitrifying bacteria. b) Phytoplankton : In an aquatic ecosystem, phytoplankton are the major autotrophs. Phytoplanktons may produce as much food as produced by the larger shrubs and trees in unit area. CONSUMERS • All the heterotrophs of the ecosystem are known as consumers. It includes micro-organisms. These directly (on herbivores) or indirectly (on carnivores) depend on the producers for food. • Types of consumer are : macroconsumers and micro-consumers. • Macroconsumers / Phagotrophs or holozoic digest their food inside the body of organism i.e. first ingestion then digestion. • Macro-consumers are of following type : a) Primary consumer : Such living organisms which obtain food directly from producers or plants are known as primary consumers. E.g., Herbivores of ecosystem, cow, grazing cattle, rabbit. They are also known as secondary producers as they synthesize complex materials in the cells by the digestion of food which is obtained from the plant. b) Secondary consumers or primary carnivores: Those animals which feed upon primary consumers and obtain food. Those carnivores which kill and eat the herbivores are called predators. E.g., dog, cat, snake. In aquatic system, whale is a secondary consumer. It is an example of a filter feeder because it feeds on plankton. c) Top (tertiary) consumers : Those animals which kill other animals and eat them, but are not killed & eaten by other animals in nature are called tertiary consumers. E.g., Lion, man, peacock. • Micro-consumers/Decomposers or Scavengers/Osmotrophs are those living organisms which decompose the dead body of producers and consumers. • The main decomposers in ecosystem are bacteria and fungi. • Decomposers play a significant role in mineral cycle. ABIOTIC COMPONENTS • Abiotic components include inorganic substances or minerals; organic substance and atmospheric factor. • Inorganic substances are P, S, N, H, Mg, K, CO2, NO2 etc. These are raw materials for plants. • Organic substances are proteins, carbohydrates, lipids in dead organic substances. • Atmospheric factors are light, temperature, humidity, rain, water, gas etc. PRODUCTIVITY • Productivity of the ecosystem refers to the rate of biomass production i.e. the amount of organic matter accumulated per unit area per unit time. • It is generally expressed in g–2 yr –1 or (kcal m–2) yr–1. • There are two types of productivity- primary and secondary. PRIMARY PRODUCTIVITY • Primary productivity is defined as the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis. • Primary productivity depends on the plant species inhabiting a particular area. It also depends on a variety of environmental factors, like, availability of nutrients and photosynthetic capacity of plants. Therefore, it varies in different types of ecosystems. • The annual net primary productivity of the whole biosphere is approximately 170 billion tons (dry weight) of the organic matter. • Productivity of the ocean is only 55 billion tons. • In per unit area, maximum productivity is found in tropical rainforest. • In water, least productive ecosystems are very deep lakes and highly productive ecosystems are coral reefs. • Nitrogen is the limiting factor in ocean and phosphorus is the limiting factor in lake productivity. • Most productive agro-ecosystem is sugarcane and rice ecosystem - 3 - 4 kg/m sq/year. • Primary productivity can be divided into - gross primary productivity (GPP) and net primary productivity (NPP). • Gross primary productivity (G.P.P.) is the total amount of energy fixed (organic food) in an ecosystem (in producers) in unit time including the organic matter used up in respiration during the measurement period. It is also known as total (gross) photosynthesis. A considerable amount of GPP is utilized by plants in respiration. • Net primary productivity (N.P.P.) is the amount of stored organic matter in plant tissues after respiratory utilization. NPP = GPP – R (R = Respiration + Metabolic activities) . or GPP = NPP + R SECONDARY PRODUCTIVITY • Secondary productivity is the rate of formation of new organic matter by consumers. • The food of consumers has been produced by the primary producers & secondary productivity reflects only the utilization of this food for the production of consumer biomass. • Net community productivity or Net productivity is the rate of storage of organic matter not used by the heterotrophs NCP = N.P.P. – HR (HR = Energy used by heterotrophs or consumers) ECOLOGICAL EFFICIENCY (EE) [EXTRA INFORMATION FOR ENTRANCE EXAMINATIONS] The percentage of energy transferred from one trophic level to the next is called ecological efficiency or food chain efficiency. Ecological efficiencies may be expressed as – • Assimilation efficiency (AE) It is the proportion of consumed energy that is assimilated. • Net production efficiency (NPE) It is the percentage of net primary productivity in relation to gross primary productivity. • Photosynthetic efficiency (PE) It is the percentage of incident solar radiation trapped by producers to perform photosynthesis & produce gross primary productivity. Photosynthetic efficiency is 1-5%. It can also be expressed in relation to PAR when it is 2-10%. • Ecological efficiency(EE)/trophic level efficiency (TLE) : It is the percentage of energy converted into biomass by a higher trophic level over the energy of food resources available at the lower trophic level. DECOMPOSITION • Decomposers are responsible for converting complex organic material of dead minerals or plants into simpler organic matter through the process of decomposition and release mineral substances into the soil where these are reused by the producers, so that soil is considered as the best resource of minerals. • The upper layer of the soil is the main site for decomposition process in the ecosystem. • The process of decomposition involves several processes. These processes can be categorised as: A. Fragmentation of detritus B. Leaching C. Catabolism D. Humification E. Mineralization • Detritivores (e.g., earthworm) breakdown detritus into smaller particles (called fragmentation). • By the process of leaching, water soluble inorganic nutrients' go down into the soil horizon and get precipitated as unavailable salts. • In bacteria and fungi, process of decomposition completely takes place outside the body. They carry out catabolism and release extracellular enzymes from their body on dead remains and decompose it into simpler organic substances and then absorb it. So these are called as osmotrophs (absorptive). • In the process of decomposition, some nutrients get tied up with the biomass of microbes and become temporarily unavailable to other organisms. Such incorporation of nutrient in living microbes (bacteria & fungi) is called nutrient immobilisation. • Humification and mineralization occur during decomposition in the soil. Humification leads to formation of humus which is highly resistant to microbial action & undergoes extremely slow decomposition. Humus serves as a reservoir of nutrients. • Mineralization results in the release of inorganic substances (e.g., CO2, H2O) + ++ ++ + and variable nutrients (NH4 , Ca , Mg , K etc.) in the soil. • Decomposition is largely an oxygen requiring process. Factors affecting decomposition – a. Temperature and soil moisture are important and regulate decomposition through their effects on the activates of soil microbes. b. Warm and moist environment favour decomposition whereas low temperature and anaerobiosis inhibit decomposition. Fig. : Diagrammatic representation