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Chapter 22 Ecosystems and the Biosphere 22-1 Energy Transfer In an ecosystem, energy flows from the sun to autotrophs and then to other organisms Autotrophs make their own food (plants and some bacteria and protists) Producers Most producers are plants Photosynthesis: plants use carbon dioxide, water, and solar energy to make glucose. (Oxygen is a byproduct) 6 CO2 + 6 H2O + solar energy C6H12O6 + 6 O2 Chemosynthesis Some species of bacteria can produce carbohydrates from inorganic molecules Example: bacteria found along hydrothermal vents in the ocean Measuring Productivity Gross primary productivity: the rate that producers in an ecosystem capture energy Biomass: organic material Only energy stored as biomass is available to other organisms Net Primary Productivity The rate at which biomass accumulates in an ecosystem Can vary greatly in different ecosystems Influenced by light, temperature, and precipitation Consumers Organisms that get their energy by eating other organisms Also called heterotrophs (“other feeders”) Examples: animals Herbivores Consumers that eat only producers (plant eaters) Examples: rabbits, deer, cows, sheep, grasshoppers Carnivores Consumers that eat only other consumers (meat eaters) Examples: coyote, bobcat, shark, alligator, hawk, owl, snakes Omnivores Consumers that eat both plants and animals Examples: humans, bears, pigs, gorillas, rats, raccoons, some insects Detritivores Consumers that feed on dead organisms, animal waste, or fallen leaves and branches Examples: vultures, maggots, carrion beetles, earthworms Decomposers Consumers that break down dead organisms in an ecosystem (returns nutrients to soil, water, and air) Examples: fungi and bacteria Energy Flow Cellular respiration: breaking down food to yield energy C6H12O6 + 6 O2 6 CO2 + 6 H2O + energy Cells use glucose and oxygen to produce carbon dioxide, water, and energy Food Chain A sequence in which energy is transferred from one organism to the next as each organism eats another organism Represents one strand of a food web Food Web Shows many feeding relationships that are possible in an ecosystem DDT Dichloro-Diphenyl-Trichloroethane Pesticide once used to prevent mosquitoes from transmitting malaria to humans Contaminated zooplankton small fish large fish eagles and ospreys Biomagnification DDT became more concentrated as it moved up the food chain Caused eggshell thinning in eagles and ospreys Banned in 1972, but is still present in some ecosystems Migratory birds are exposed to DDT in other countries that still use it Trophic Levels Refers to each step in the transfer of energy through a food chain or a food web Each time energy is transferred, some energy is lost and less energy is available to the next trophic level Energy Pyramid Energy Loss Since so much energy is lost at each level, there are fewer organisms at the higher trophic levels Ecosystems rarely have more than 4-5 trophic levels Quantity of Energy Transfers 10% of the total available energy at one trophic level is transferred to the next level Higher trophic levels contain less energy and can support fewer organisms 22-2 Ecosystem Recycling Biogeochemical cycles: The movement of water, minerals, and elements through the environment Examples: the water, carbon, nitrogen, and phosphorus cycles The Water Cycle Water is a renewable resource because it is circulated through the water cycle The water cycle is the continuous movement of water between Earth and the atmosphere Global Water Distribution 97% of Earth’s water is saltwater 3% is freshwater, but most of it is frozen as icecaps or glaciers Less than 1% is available as liquid freshwater Watershed An area of land drained by a river Pollution anywhere in a watershed can pollute a river The Carbon Cycle A process by which carbon is cycled between the atmosphere, land, water, and organisms Carbon is present in all living things Short-term cycle Consumers eat producers and obtain carbon from the carbohydrates Some of the carbon is released back into the atmosphere as a byproduct of cellular respiration Long-term cycle Carbonates (found in bones, shells, & coral) do not break down easily Calcium carbonate deposits form limestone Limestone is one of the largest carbon sinks on Earth Fossil Fuel When living organisms die, their remains still contain carbon Over time, the remains of ancient organisms changed into coal, oil, and natural gas Humans and the Carbon Cycle When we burn fossil fuels, we release carbon dioxide into the atmosphere Increased levels of carbon dioxide contributes to global warming The Carbon Cycle The Nitrogen Cycle The process by which nitrogen is cycled between the atmosphere, bacteria, and other organisms The atmosphere is 78% nitrogen, yet most organisms (including humans) cannot use it until it has been “fixed” Nitrogen-Fixing Bacteria Legume plants, such as soybeans and clover, have root nodules that contain nitrogen-fixing bacteria The bacteria “fixes” the nitrogen into a usable form All Life is Interconnected All organisms need nitrogen to build proteins The bacteria alter the atmospheric nitrogen for plants to use Animals obtain the nitrogen they need when they eat plants Decomposers Bacteria break down wastes and dead organisms to return nitrogen to the soil Some of the nitrogen is transformed into a gas and is returned to the atmosphere The Nitrogen Cycle The Phosphorus Cycle The movement of phosphorus from the environment to organisms and then back to the environment This cycle is very slow Phosphorus moves from phosphates in rock to living organisms and eventually to the ocean Phosphates When rocks erode, they release phosphates into the soil and water Plants absorb phosphates through their roots Phosphates are also added to the soil when organisms die and decompose The Phosphorus Cycle Fertilizers Fertilizers contain both nitrogen and phosphorus Fertilizers can enter an aquatic ecosystem through runoff Excess nitrogen and phosphorus in an aquatic ecosystem can result in an algal bloom Artificial Eutrophication Sewage and fertilizer runoff enter lakes and ponds and causes an algal bloom When the algae dies, the decomposition from bacteria uses most of the oxygen and the fish suffocate and die 22.3 Terrestrial Ecosystems Biomes: very large terrestrial ecosystems that contain specific kinds of plants and animals Biomes are influenced by climate and altitude Climate & Altitude Climate: the temperature and precipitation of an area over a long period of time Altitude: refers to the elevation above sea level Biomes Each biome is made up of many different types of ecosystems. There are seven major biomes: tundra, taiga, temperate deciduous forest, temperate grassland, desert, savanna, and tropical rainforest Biomes of the World Tundra A cold biome located across northern North America, Europe and Asia The ground is permanently frozen at a depth of 10-36 inches (trees can't grow) Receives little precipitation and a very short growing season (2 months) Common Plants & Animals of the Tundra Plants: grasses, sedges, mosses, and lichens Animals: caribou, musk ox, lemmings, snowshoe hares, snowy owls, arctic fox Taiga A forested biome dominated by conifers (pine, fir, hemlock, and spruce) Needles are specialized leaves that help the trees survive the long, cold winters Common Plants & Animals of the Tiaga Plants: evergreen trees Animals: lynx, moose, bears, wolves, great gray owls Temperate Deciduous Forest Characterized by trees that lose their leaves in the Fall Variable temperatures and moderate precipitation Common Plants & Animals of the Temperate Deciduous Forest Plants: beech, maple, oak, hickory, sycamore, elm, birch Animals: white-tailed deer, raccoons, foxes, squirrels, great-horned owls Temperate Grasslands Regions that are dominated by grasses and have variable temperatures Found in the interior of continents Also called prairies, steppes, pampas, and veldt Common Plants & Animals of the Temperate Grassland Plants: various grasses (a lot has been turned into farmland!) Animals: pronghorn, prairie dogs, meadowlark, bison Deserts Areas that receive less than 25 cm of rainfall per year Most deserts are hot, but there are also cold deserts Desert vegetation is sparse and has a waxy coating that prevents water loss Rain Shadow Effect Common Plants & Animals of the Desert Plants: cacti and succulents Animals: lizards, scorpions, jack rabbits, roadrunners, kit fox, snakes, burrowing owls Savannas Tropical or Subtropical grasslands with scattered trees and shrubs Has alternating wet and dry seasons Common Plants & Animals of the Savanna Plants: various grasses, few trees, shrubs Animals: wildebeest, zebras, gazelles, giraffe, lions, cheetahs, elephants Tropical Rain Forests Areas near the equator that have a warm, wet climate and a year-round growing season Most biodiversity is found in tropical rainforests Common Plants & Animals of the Tropical Rain Forest Plants: trees, epiphytes, understory plants Animals: parrots, jaguar, monkeys, insects, sloth, snakes, lizards (contains 1/5 of all known species) 22-4 Aquatic Ecosystems Water covers ¾ of Earth 97% of all water on our planet is saltwater 3% is freshwater (less than 1% is liquid freshwater!) Ocean Zones Photic Zone: the part of the ocean that receives light Aphotic Zone: the cold, dark depths where sunlight doesn’t reach The Intertidal Zone The area that includes the beaches, tidal pools, and waves Organisms are adapted to the rise and fall of the tides Tides Tides are the cyclic rising and falling of Earth's ocean surface caused by the tidal forces of the moon and the sun acting on the oceans High and Low Tides During the day, the Earth rotates 180 degrees in 12 hours. The moon, meanwhile, rotates 6 degrees around the earth in 12 hours. The moon's rotation and its gravitational pull mean that any given coastal city experiences a high tide approximately every 12 hours Spring Tide When the sun and moon are aligned, there are exceptionally strong gravitational forces, causing very high and very low tides which are called spring tides, though they have nothing to do with the season. Neap Tides During the moon's quarter phases the sun and moon work at right angles, causing the bulges to cancel each other. The result is a smaller difference between high and low tides. The Neritic Zone The most productive zone in the ocean Upwelling refers to currents that carry nutrients up from the bottom Coral reefs, plankton, sea turtles, fish, squid, etc. are found in this zone Coral Reefs Limestone ridges built by coral polyps Very diverse ecosystem Corals are invertebrates that only live in shallow tropical seas Threats to Coral Reefs Coral reefs are fragile Divers cut pieces of coral to sell Also threatened by oil spills, pollution, sewage, pesticides, and silt runoff The Oceanic Zone Nutrient levels are lower in this zone Deep sea organisms have reduced skeletons and slower metabolism Threats to the Oceans OVERFISHING! Trawl nets entangle and kill many animals Industrial waste, sewage, solid waste, oil spills, toxic chemicals Hydrothermal Vents Areas that release water that is rich in minerals and can exceed 750 °C Chemosynthetic bacteria uses hydrogen sulfide (H2S) to make their own food Many organisms along a vent get their food directly from the bacteria Estuaries Areas where freshwater rivers and streams flow into the sea Examples: bays, salt marshes, mud flats Receive a lot of light and nutrients Important breeding grounds for many species Freshwater Zones Freshwater contains less than .005 % salt (NaCl) Examples: lakes, ponds, streams, & rivers Lakes and Ponds Eutrophic: rich in organic matter and vegetation Oligotrophic: contains little organic matter Rivers Bodies of water that flow down a gradient Headwaters: where a river begins (usually as a mountain stream) As a river flows down a mountain, it becomes wider, warmer, slower, and has less oxygen Streams Tributaries that flow into larger bodies of water Faster flowing streams are highly oxygenated and contain more benthic macroinvertebrates