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TOPIC: Food Chain, Food Web and Food Pyramid The phrase 'food chain' is a way of indicating how energy moves through an ecosystem. Food chains are more often called food webs because no organism lives solely on another. A food chain is a possible route for the transfer of matter and energy (food) through an ecosystem from autotrophs through heterotrophs and decomposers. Example of food chains: • Producer →primary consumer → secondary consumer → tertiary consumer → decomposer • Grass →rabbit → fox → decomposer (upon the death of the fox) Components of a Food Chain: The food chain consists of four main parts: 1. The Sun, which provides the energy for everything on the planet. 2. Producers: these include all green plants. These are also known as autotrophs, since they make their own food. Producers are able to harness the energy of the sun to make food. Ultimately, every (aerobic) organism is dependent on plants for oxygen (which is the waste product from photosynthesis) and food (which is produced in the form of glucose through photosynthesis). They make up the bulk of the food chain or web. 3. Consumers: In short, consumers are every organism that eats something else. They include herbivores (animals that eat plants), carnivores (animals that eat other animals), parasites (animals that live off of other organisms by harming it), and scavengers (animals that eat dead animal carcasses). Primary consumers are the herbivores, and are the second largest biomass in an ecosystem. The animals that eat the herbivores (carnivores) make up the third largest biomass, and are also known as secondary consumers. This continues with tertiary consumers, etc. 4. Decomposers: These are mainly bacteria and fungi that convert dead matter into gases such as carbon and nitrogen to be released back into the air, soil, or water. Fungi, and other organisms that break down dead organic matter are known as saprophytes. Even though most of us hate those mushrooms or molds, they actually play a very important role. Without decomposers, the earth would be covered in trash. Decomposers are necessary since they recycle the nutrients to be used again by producers. Types of Food Chains: Grazing food chain - The grazing food chain begins with the photosynthetic fixation of light, carbon dioxide, and water by plants (primary producers) that produce sugars and other organic molecules. Once produced, these compounds can be used to create the various types of plant tissues. Primary consumers or herbivores form the second link in the grazing food chain. They gain their energy by consuming primary producers. Secondary consumers or primary carnivores, the third link in the chain, gain their energy by consuming herbivores.Tertiary consumers or secondary carnivores are animals that receive their organic energy by consuming primary carnivores. Detrital food chain - The detritus food chain differs from the grazing food chain in several ways: the organisms making it up are generally smaller (like algae, bacteria, fungi, insects, & centipedes) the functional roles of the different organisms do not fall as neatly into categories like the grazing food chain's trophic levels. detritivores live in environments (like the soil) rich in scattered food particles. As a result, decomposers are less motile than herbivores or carnivores. Decomposers process large amounts of organic matter, converting it back into its inorganic nutrient form. Food Web A food web shows all possible feeding relationships in a community at each trophic level; represents a network of interconnected food chains. An example of a food web: The difference between a food chain and a food web is that a chain is a single strand of the different levels of energy transfer, where as a food web will show the many strands in a particular ecosystems such as a forest. Food Pyramid A food pyramid, or ecological pyramid, will show population sizes (amount of energy at that level) in an ecosystem. The pyramid most often decreases, as it gets farther up. In the example of the food web above, a food pyramid can be created with the clover, the worm, and the raccoon. There is a much larger abundance of clover than the other two; they will be on the bottom of the pyramid. The worm will be the next step with a smaller number than clover, but larger number of raccoon. The raccoon will be on the top of the pyramid with the smallest number. The pyramid will look like this: Racoon Worm Clover Interactions Among Organisms Any relationship in which there is a close and permanent association between organisms of different species is symbiosis, or “living together”. There are several types of symbiosis. They are predation, parasitism, commensalism, and mutualism. Predation is a relationship in which one organism preys on another as a source of food. An example of predation is an owl hunting a field mouse. Parasitism is a relationship in which one organism derives benefit at the expense of the other. An example of parasitism is a tapeworm living in the intestines of dogs. The tapeworm takes nourishment from the dog in which it lives. Pathogens that cause diseases in plants and animals are parasites. Parasites are responsible for such diseases as malaria, polio, and influenza in humans. Plant diseases include wheat rust, corn smut, and Dutch elm disease. If a host dies prematurely from disease, however, the pathogen is also at risk of dying. As a result, many parasites and their hosts have evolved a form of mutual tolerance; nevertheless, the host is still harmed in some way. Commensalism is a relationship in which one organism derives benefit with neither benefit nor harm to the other. Birds and squirrels nesting in trees and shrubs can be thought of as examples of commensalism. The benefits are obvious - shelter from the elements and protection from predators. Host trees and shrubs are not affected by the presence of nests. Mutualism is a relationship in which both organisms benefit from each other. An example of a mutualistic relationship is that of the ant and the acacia tree. The ant protects the tree from herbivores from eating the tree as well as clearing vegetation away from the tree that may compete for resources. The tree provides a home for the ants. Clown fish and sea anemones-bright and colorful clown fish live in and amongst the tentacles of the sea anemone, which look like beautiful aquatic flowers, but bear poisonous stinging cells called nematocysts. A slime layer covering the clownfish make them immune to the stinging cells, and the stinging tentacles of the sea anemone deter potential predators. The clownfish in turn protect the sea anemone from other fish that would feed on the anemone. Clownfish laid eggs within the sea anemone, which offers protection during their incubation and development. Predator-prey interactions - the interaction between predators and prey involve continuous evolutionary change; as predators evolve more efficient ways of capturing prey, the prey evolve ways of avoiding predation. For example: 1. Warning coloration, mimicry, & cryptic coloration: Warning coloration - conspicuous markings of an animal that make it easily recognizable and warn would-be predators that it is a poisonous, foul-tasting, or dangerous species mimicry - the advantageous resemblance of one species to another, often unrelated, species or to a feature of its own environment. cryptic coloration - an organism matches its background, hiding (camouflaging) it from predators and/or prey. 2. Chemical defenses serve to repel or inhibit potential predators commonly employed by arthropods, amphibians, & snakes also used extensively by various types of plants 3. Predator satiation timing reproduction so that a maximum number of offspring are produced in a short period of time, thus satiating predators and allowing a greater percentage of young to survive examples of organisms that use this strategy include wildebeest, cicadas, caribou , and lots of plants Biogeochemical Cycling The transport and transformation of substances in the environment, through life, air, sea, land, and ice, are known collectively as biogeochemical cycles. These global cycles include the circulation of certain elements, or nutrients, upon which life and the earth's climate depend. Carbon cycle - the movement of carbon, in its many forms, between the biosphere, atmosphere, oceans, and geosphere plants obtain carbon dioxide from the air and, through photosynthesis, incorporate carbon into their tissues producers & consumers - transform part of the carbon in their food back into carbon dioxide via respiration decomposers - release the carbon tied up in dead plants & animals into the atmosphere Another major exchange of carbon dioxide occurs between the oceans and the atmosphere. The dissolved CO2 in the oceans is used by marine biota in photosynthesis. Two other important processes are fossil fuel burning and changing land use. In fossil fuel burning, coal, oil, natural gas, and gasoline are consumed by industry, power plants, and automobiles. Changing land use is a broad term which encompasses a host of essentially human activities, including agriculture, deforestation, and reforestation. Environmental Issues: The global carbon cycle is out of balance, making rapid global climate change more likely. Atmospheric CO2 levels are rising rapidly -- currently, they are 25% above where they stood before the industrial revolution. Carbon dioxide forms when the carbon in biomass oxidizes as it burns or decays. Many biological processes set in motion by people release carbon dioxide. These include burning fossil fuels (coal, oil, & natural gas), slash-and-burn agriculture, clearing land for permanent pasture, cropland, or human settlements, accidental and intentional forest burning, and unsustainable logging and fuelwood collection. Clearing vegetation cover from a forested hectare releases much of the carbon in the vegetation to the atmosphere, as well as some of the carbon lodged in the soil. Logging or sustainable fuelwood collection can also degrade vegetation cover and result in a net release of carbon. Nitrogen cycle - Almost all of the nitrogen found in terrestrial ecosystems originally comes from the atmosphere. Small proportions enter the soil in rainfall or through the effects of lightning. Most, however, is biochemically fixed within the soil by specialized micro-organisms like bacteria. Members of the bean family (legumes) and some other kinds of plants form mutualistic symbiotic relationships with nitrogen fixing bacterial. In exchange for some nitrogen, the bacteria receive from the plants carbohydrates and special structures (nodules) in roots where they can exist in a moist environment. Scientist estimate that biological fixation globally adds approximately 140 million metric tons of nitogen to ecosystems every year.