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Ecosystems and Energy Transfers WONG HONG CHING Index • 1. Definition of key words • 2. Energy transfers in ecosystems • 3. Ecological pyramids 1. Definition of key words • Ecosystem • Population • Community • Habitat • Niche • Environment Ecosystem • Ecosystem stands for Ecological system. • It is an ecological unit which includes all living organisms and the abiotic factors that surround the organisms, results from the dynamic interactions abiotic and biotic factors. • The abiotic factors: • • • • • • Temperature pH Light intensity Oxygen level Humidity Rainfall • The biotic factors: • • • Animals Plants Micro-organisms Population & Community • Population refers to all the organisms of the same species in a area. • Community refers to all living organisms of different species living in a given area. • Living organisms interact with each other and are interconnected by food chains or food webs. Habitat • Habitat refers to the place where the communities live. • Examples of habitats: • • • • Forest Sea Rock shore Soil Niche • It is a word which is used to describe the relational position of a species in an area. • It refers to the roles of an organism in an area. • Different species have different roles, niches. • Roles: • • • • What it eats Where it lives When it is active When it eats Environment • Environment is the conditions surrounding the organisms. • The conditions include both abiotic factors and biotic factors. • The abiotic factors: • • • • • • Temperature Rainfall pH Light intensity Oxygen level Humidity • The biotic factors: • • Predation by other organisms Competition of nutrients, food Energy transfers Cycle • First step: • Solar energy Plants (Act as producers) • Second step: • Producers’ energy Primary consumer (herbivores) • Third step: • Primary consumers’ energy Secondary consumers (carnivores) • Forth step: • Secondary consumers’ energy Tertiary consumers • Final step: • When tertiary consumers die, the energy and nutrients are returned to the soil by saprotrophic organisms which feed on dead organisms. • Decomposers: Start the cycle again Energy Transfers in Ecosystem • Is the energy totally transferred between different trophic levels? • The answer is no. • Only 10% energy is transferred between different trophic level. WHY?? • 30% of energy is used in respiration. • 60% of energy is lost in excretion of waste products, like faeces, urine, gas. • Amount of energy stored and transferred to another trophic level: • 100% - 30% - 60% = 10% • No food chain can exceed more than 5 links. • Otherwise, the consumers at the end of food chain cannot get enough food and energy. Ecological Pyramids • What is ecological pyramids? • They are the graphs which are used to show the relationship between energy and trophic levels of an area. • Three types of pyramids: • Pyramid of number • Pyramid of biomass • Pyramid of energy Feature: Primary producers are at the bottom. Pyramid of number • Feature: • It is a ecological pyramid which shows the number of organisms in different trophic levels. • Advantage: • Just counting the number of organisms, is easy to produce. • Disadvantages: • The pyramid shape is messed up by small amount of big producers (like trees) and large amount of tertiary producers (like fleas). Abnormal cases of pyramids of number • Small amount of large producers. • Large amount of small tertiary consumers. Pyramid of biomass • It is a ecological pyramid which measures the dry mass of organisms in different trophic levels. • The unit of dry mass is kg/m2 • Advantage: • Pretty accurate, often have a normal pyramid shape. • Disadvantages: • Difficult to get the data. (Need to kill the organism and evaporate all of it’s water inside the body) • If the producers have small sizes, short life and reproduces quickly, then the pyramid shape is distorted. Pyramid of energy • It is a ecological pyramid which measures the amount of energy in the organisms in different trophic levels. • The unit is kJ/m-2/yr-1 • It is the most accurate among other pyramids. • However, it is very difficult to measure the amount of energy in the organism. Bibliography • http://ecokids.ca/pub/eco_info/topics/frogs/chain _reaction/index.cfm • http://www.arcytech.org/java/population/facts_foo dchain.html