Ecology - Exchange of energy and matter

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1 - Exchange of energy and matter You should be able to: (a) briefly describe the non-cyclical nature of energy flow (b) establish the relationship of the following in food webs: producer, consumer, herbivore, carnivore, decomoser, food chain, trophic level (c) describe energy losses between trophic levels and infer the advantages of short food chains (d) interpret pyramids of numbers and biomass (e) explain the importance of the carbon cycle 1. is the study of the relationships of living organisms with each other and their non-living or physical surroundings. Such studies give the basic framework for our understanding of agriculture, forestry and fisheries, and also is the basis for predicting, preventing and remedying pollution. also helps us to understand the likely consequences of creating changes in the environment (eg. the building of dams). 2. The Ecosystem An ecosystem is an ecological system formed by the interaction of living organisms and their non-living environment. Hence, both the abiotic and biotic components operating in such a system should be considered in an ecosystem. Abiotic environment: Non-living, physical factors (eg. Light, oxygen, water, ph, salinity, temperature) which involve matter and energy. Biotic environment: Consists of all living things an organism comes into contact with. Habitat: The place where an organism lives (eg. Pond, stream, river, forest). Ecological niche: The function of an organism or the role it plays in the habitat (where it lives and what it does there). The different ecosystems together form the biosphere/ecosphere which includes all living organisms and the physical environments with which they interact. Lesson Notes 1

2 Maris Stella High School O Level Science Biology Topic 14.1 Ecosystem: Consists of the biotic component (the living organisms, populations, communities), and the abiotic component (non-living part) and the interactions of the living organisms, and their abiotic environment. The abiotic component includes soil, water (which both contain a mixture of inorganic and organic nutrients), and climate (includes environmental variables like light, temperature, humidity, rain or snow) Community: Consists of different populations of plants and animals living together and interacting within the same environment. The different populations would live interdependently. Population: Consists of a group of individuals of the same species occupying a given area. It is expressed in terms of density (number of individuals per unit area). The rate of change of a population depends on the birth rate (or the number of new individuals added to it), the death rate and migration. A population increases when the number of new individuals added to it exceeds the number lost through death or migration & vice versa. Note: An organism in any habitat is never an independent unit. Its daily existence depends on and is influenced by other organisms around it. Lesson Notes 2

3 3. Energy flow & biogeochemical cycling Energy is required by living organisms to maintain life processes. The energy that powers most ecosystems is ultimately from the Sun. Solar energy is captured by autotrophs in photosynthesis, which in turn form the food source for all other organisms in the ecosystem. The chemicals found in living organisms are derived originally from the abiotic component of the ecosystem, for example, water and air. These chemicals would return back to the environment by way of the decomposition of the waste products or dead bodies of organisms, which is carried out by bacteria & fungi. The decomposers obtain energy from the waste products and dead organisms in the process. Therefore, there is a constant cycling of chemical materials required by living organisms within the ecosystem. As both living and non-living parts of the ecosystem are involved in the cycle, they are known as biogeochemical cycles. While the chemicals are constantly recycled and used, some of the energy in the ecosystem is changed into forms which cannot be used again by the system (mainly heat energy). Thus, to maintain the ecosystem, regular and frequent inputs of solar energy are needed. Note: Chemicals are recycled and energy flows through ecosystems. Light energy Heat energy SUN Biotic component Nutrients Abiotic component ENERGY FLOW Nutrient Cycling/ Biogeochemical Cycling Lesson Notes 3

4 4. Food Chains & Trophic Levels Energy-containing organic molecules produced by autotrophs are the source of food (containing both materials and energy) for heterotrophs. These animals are in turn eaten by other animals, and thus energy is transferred through a series of organisms, each feeding on the preceding organism and providing raw materials and energy for the next organism. This sequence is known as a food chain. Each stage of the food chain is known as a trophic level: 1 st trophic level: Producers (autotrophic, usually green plants and algae) 2 nd trophic level: Primary consumers (Feed on producers, known as herbivores) 3 rd trophic level: Secondary consumers (Feed on herbivores, known as carnivores) 4 th trophic level: Tertiary consumers (Feed on secondary consumers, also carnivores) Secondary and tertiary consumers may be: - Predators: Hunt, capture and kill prey - Carrion feeders: Feed on corpses - Parasites: Feed off the host organism while it continues to live Dead organisms and waste material passed from the bodies of living organisms are sources of energy and raw materials (nutrients). These form the food for organisms known as decomposers and detritivores. Decomposers: Microorganisms (mainly fungi & bacteria) which are saprophytes and live on dead organic matter. They secrete digestive enzymes onto the material and absorb the products of digestion. Detritivores: Feed on small pieces of decomposing or dead material (detritus). Usually in food chains: - There are four or five trophic levels, and seldom more than six. Why? - Carnivores become larger and fewer in numbers at each successive trophic level. - Parasites get smaller at successive trophic levels and usually increase in number. Lesson Notes 4

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6 5. Food Webs In ecosystems, feeding relationships are complex, and most organisms would feed on more than one other organism. Some animals, including humans, feed on organisms at all trophic levels (plants, animals, fungi), and are known as omnivores. The mesh of interlinking food chains in an ecosystem is known as a food web. Lesson Notes 6

7 6. Ecological Pyramids Feeding relationships and the efficiency of energy transfer through the biotic component of ecosystems can be summarized in pyramid diagrams. This allows different ecosystems to be compared, as well as observations of the effect of changes in the ecosystem as well as seasonal variations. Pyramid of Numbers - Based on counting the numbers of organisms at each trophic level in a given area. - Usually a decrease in the number of organisms at each successive level is found. - The number of organisms in a given trophic level is represented as a rectangle whose length/area is proportional to the number of organisms in a given area or volume (if it is an aquatic ecosystem). - Advantage: Data is relatively easy to collect. - Disadvantages: o Trophic level is hard to ascertain for certain organisms. o Range of numbers may be very great, causing difficulties in drawing the pyramid to scale. o Producers are varied in size, sometimes resulting in a true pyramid shape not being obtained. Pyramid of Biomass - Based on the weight (usually dry weight) of organisms at each trophic level. - Dry mass should be compared ideally (estimated from wet mass or samples must be dried and weighed). - Advantage: More accurate than pyramid of numbers. - Disadvantages: o More laborious and costly to obtain data. o Destructive methods may be used to obtain dry masses. Pyramid of Energy (not in syllabus) - Based on the energy content of the organisms at each trophic level in a given area/volume and period of time. - Most useful but obtaining of data is the most difficult. Lesson Notes 7

8 7. The Carbon Cycle The various processes by which carbon, in the form of carbon dioxide, is removed and restored to the atmosphere constitute the carbon cycle. The importance processes which bring about recycling of carbon dioxide between the biotic and abiotic components of the ecosystem are photosynthesis, respiration, and decay all processes carried out by the living organisms. The cycling of carbon (and all other nutrients as well) is essential for an ecosystem to function. The carbon cycle: Ensures that there is a continuous supply of inorganic carbon dioxide for plants to carry out photosynthesis a process that converts solar energy into chemical energy (food) which other non-photosynthetic organisms can use to stay alive. Enables a linear flow of energy through the ecosystem. The carbon compounds are vehicles through which solar energy (converted to chemical energy) passes from organism to organism in the food chains of an ecosystem. Lesson Notes 8

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