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Chapter 3 How Ecosystems Work You could cover the whole world with asphalt, but sooner or later green grass would break through.” Ilya Ehrenburg Energy Flow in Ecosystems • For most living organisms the sun is the ultimate source of it’s energy. • The suns energy is captured by organisms that can do photosynthesis. All green plants, some bacteria and a few protists. • Energy can then be transferred to other organisms. Energy Relationships • Producers are organisms that can produce their own food. Also known as autotrophs (self-feeders). • Consumers are organisms that get their energy from eating other organisms. Also known as heterotrophs (other-feeders). • Producers get their energy directly from the sun. Consumers get their energy indirectly from the sun. Chemosynthetics • Not all organisms use the sun as their energy source. • Some bacteria can use the chemical energy found in sulfide and nitrogen compounds. Also known as chemotrophs (chemical – eaters). • Found in deep – ocean ecosystems. Recent research has shown that these ecosystems may contain more than 50% of the worlds biomass. Who eats what? • Within an ecosystem there are various relationships. • Herbivores – consumers that only eat producers. • Carnivores – consumers that eat only other consumers. • Omnivores – consumers that eat both producers and other consumers. The most versatile organisms in the ecosystem. • Decomposers – break down dead organisms, producers and consumers. Return nutrients to the ecosystem. Cellular Respiration • The process that all living things use to obtain energy from nutrients. • Done by both autotrophs and heterotrophs. • Can be aerobic or anaerobic. • Some organisms are strictly aerobic or anaerobic. Others can switch back & forth depending on conditions (facultative anaerobes). Energy Transfer • As organisms are eaten or decompose, energy is transferred. • This transfer of energy can be tracked and mapped using food chains, food webs, and trophic levels. Food Chains & Food Webs • Food chain - a sequence that shows the transfer of energy from one organism to the next. Usually linear in nature. • Can also be used to show the movement of toxins/poisons through the food chain. • Food webs – more accurate depiction of the energy transfer. Shows all of the feeding relationships in the ecosystem. Made up of a number of interconnected food chains. Trophic Levels • Each step in the energy transfer within an ecosystem is called a trophic level. • Each time energy is transferred from one trophic level to the next some is lost. • Usually figure that only 10% of the energy is transferred between trophic levels. • Some decomposer food webs can show higher efficiencies (20-40%). Trophic Levels • Due to the energy loss, usually find fewer organisms at the higher trophic levels. • Almost always find the producers to be the largest number (the most energy available). • Energy loss also usually limits the number of trophic levels available. • Seldom have more than 4 or 5, although some decomposer webs can have 8-10 trophic levels. Water Cycle • Water is physically changed in a cyclic manner. • Sunlight provides the energy that drives the water cycle. • Sunlight causes water to evaporate. As it cools, it condenses and returns as precipitation. Water Cycle (cont.) • Precipitation can take several pathways: – Some can land in the oceans. – Some can land on land. • Some can run along the surface – surface water. • Some can soak into the soil and be taken up by plants. • Some can seep through the soil and collect in aquifers – groundwater. Water Cycle (cont.) • Surface runoff can collect in streams and rivers that eventually flow into oceans. • Groundwater can flow into streams and rivers also. • Some precipitation can land on trees and either be evaporated back into the atmosphere or run down the trunk – interception. Water Cycle (cont.) • Water taken up by plants can be evaporated back by process of transpiration. • Water can also be used by domestic uses as well as industrial uses. • Development of land can alter the water cycle. Water Cycle Carbon Cycle • The carbon cycle involves changing carbon from inorganic forms to organic forms and back to inorganic forms. • Inorganic carbon (CO2) is removed from the atmosphere during photosynthesis. • Inorganic carbon is converted into organic forms (glucose, lipids, proteins, etc). Carbon Cycle (cont.) • Organic carbon is converted back into inorganic form during respiration. • Burning of fossil fuels releases inorganic carbon into the atmosphere. • Deforestation removes large producers that could help process inorganic carbon. • Increased CO2 has been linked to global warming. Carbon Cycle Carbon Cycle Nitrogen Cycle • Nitrogen needed to build proteins. • 78% of atmosphere made of N2. • Only a few bacteria can convert N2 into a useable form. Nitrogen-fixing bacteria( NH4+) • Nitrogen-fixing bacteria found free-living or within roots of certain plants (legumes). Nitrogen Cycle (cont.) • Plants convert NH4+ into amino acids and proteins. • Animals get useable nitrogen (amino acids) by eating plants or other animals. • Decomposers (bacteria & fungi) breakdown wastes & dead organisms, returning nitrogen to soil & water as NH4+ . Nitrogen Cycle (cont.) • NH4+ can be taken up by plants again and used again. • Some NH4+ can be converted into nitrates (NO3) by nitrifying bacteria. Nitrifying bacteria require aerobic conditions. • Nitrates can then be converted into N2 by denitrifying bacteria. Denitrifying bacteria require anaerobic conditions. Nitrogen Cycle Nitrogen Cycle Succession • Succession – a regular pattern of changes over time in the type of species in a community. • Process may take hundreds or thousands of years. • As species change they alter the environment, allowing new species to come in. Succession (cont.) • Eventually reach a stable, unchanging community – climax community. • When succession occurs where no ecosystem has existed before – primary succession. • When succession occurs where a ecosystem has previously existed – secondary succession. Succession (cont.) • The first plants to colonize an area – pioneers. • Eventually taller plants move in and shade out the pioneers. • The shrubs and bushes will move in and eventually trees. • Climax communities will remain stable unless there is a disturbance. Disturbance • Disturbances can be large scale or small scale. • Large scale can be forest fires, earthquakes, floods, volcanic activity, or deforestation. • Small scale disturbances can be a tree falling over. Disturbance (cont.) • Some ecosystems need periodic disturbances. • Jack pine forests need fire to disperse their seeds. • Pin cherry trees need sunlight to warm the soils for their seeds to sprout. • Man’s interference w/ natural disturbances can cause considerable damage to an ecosystem. Primary Succession • Succession that starts w/ bare rock. • Pioneer species are usually lichens & mosses. • Help break up the rock & form soil. • Allows for grasses & ferns to move in. • Grasses & ferns “crowd” out the lichens & mosses.