Ecosystems: What Are They and How Do They Work?

Ecosystems: What Are They and How Do They Work? Chapter 3 Section 3-1 WHAT KEEPS US AND OTHER ORGANISMS ALIVE? Earth s life-support system has four major components The atmosphere is the thin membrane of air around the planet. The troposphere is the air layer about 4 11 miles above sea level. It contains greenhouse gases that absorb and release energy which warms the inner layer of the atmosphere. The stratosphere lies above the troposphere between 11 31 miles; it filters out the sun s harmful radiation. The hydrosphere consists of earth s water, found in liquid water, ice, and water vapor. The geosphere is the hot core, a thick mantle, and thin crust. The biosphere includes parts of the atmosphere, hydrosphere, and geosphere. General Structure of the Earth 1

Mantle Atmosphere Soil Rock Mantle Crust Biosphere (living organisms) Geosphere (crust, mantle, core) Three factors sustain the earth s life One-way flow of high-quality energy. Cycling of nutrients. Gravity. Core Atmosphere (air) Hydrosphere (water) Fig. 3-2, p. 42 Solar radiation UV radiation Most UV absorbed by ozone Absorbed by the earth Visible light Reflected by atmosphere Lower Stratosphere (ozone layer) Troposphere added to troposphere Radiated by atmosphere as heat radiated by the earth Greenhouse effect Section 3-2 WHAT ARE THE MAJOR COMPONENTS OF AN ECOSYSTEM? Fig. 3-3, p. 42 2

Ecologists study interactions in nature Levels of Organization of Matter in Nature Ecology focuses on how organisms interact with each other and with their non-living environment. They study interactions within and among these following levels of organization: Population is a group of individuals of the same species living in a particular place. Community is populations of different species living in a particular place, and potentially interacting with each other. Ecosystem is a community of different species interacting with one another and with their nonliving environment of matter and energy Biosphere Parts of the earth's air,water, and soil where life is found Ecosystem A community of different species interacting with one another and with their nonliving environment of matter and energy Community Populations of different species living in a particular place, and potentially interacting with each other Population A group of individuals of the same species living in a particular place Key Living and Nonliving Components of an Ecosystem Organism An individual living being Cell The fundamental structural and functional unit of life Molecule Water Atom Hydrogen Oxygen Chemical combination of two or more atoms of the same or different elements Smallest unit of a chemical element that exhibits its chemical properties Stepped Art Fig. 3-4, p. 43 3

12/21/13 Ecosystems have several important components Oxygen (O2) Precipitaton Carbon dioxide (CO2) Every organism belongs to a particular trophic level depending on its source of nutrients. Producers, or autotrophs, use photosynthesis to make nutrients from components in the environment. Consumers, or heterotrophs, get their nutrients by feeding on other organisms or their remains. Consumers can be herbivores (feed on plants), carnivores (feed on animals) or omnivores (feed on both plants and animals). Producer Secondary consumer (fox) Primary consumer (rabbit) Producers Water Decomposers Soluble mineral nutrients Producers Fig. 3-5, p. 44 Consumers 4

Ecosystems have several important components Consumers can be primary, secondary or tertiary consumers, depending upon their trophic level. Decomposers (bacteria/fungi) break down organic detritus into simpler inorganic compounds. Detritivores (detritus feeders) feed on waste or dead bodies. Producers, consumers and decomposers utilize chemical energy stored in organic molecules. In most cells, this energy is released by aerobic respiration. Various Detritivores and Decomposers Detritus feeders Decomposers Main Structural Components of an Ecosystem Longhorned beetle holes Bark beetle engraving Carpenter Termite ant and galleries carpenter ant work Dry rot fungus Wood reduced Fungi to powder Time progression Powder broken down by decomposers into plant nutrients in soil Fig. 3-8, p. 45 5

Chemical nutrients (carbon dioxide, oxygen, nitrogen, minerals) Solar energy Decomposers (bacteria, fungi) Consumers (plant eaters, meat eaters) Producers (plants) Fig. 3-9, p. 46 Section 3-3 WHAT HAPPENS TO ENERGY IN AN ECOSYSTEM? Energy flows through ecosystems in food chains and food webs A food chain is a sequence of organisms, each of which serves as a source of nutrients and energy for the next organisms. Organisms are assigned to trophic levels in a food chain. Food Chain 6

Solar energy First Trophic Level Producers (plants) Second Trophic Level Primary consumers (herbivores) Third Trophic Level Decomposers and detritus feeders Secondary consumers (carnivores) Fourth Trophic Level Tertiary consumers (top carnivores) Stepped Art Energy flows through ecosystems in food chains and food webs A food web is a series of interconnected food chains. Food webs occur in most ecosystems. Organisms are also assigned to trophic levels in food webs. Producers are the first level. Primary consumers are the second. Secondary consumers belong to the third. Tertiary consumers are the fourth level. Detritivores and decomposers process detritus from all trophic levels. Fig. 3-10, p. 47 Food Web Blue whale Crabeater seal Humans Killer whale Elephant seal Sperm whale Adelie penguin Leopard seal Emperor penguin Petrel Squid Fish Carnivorous zooplankton Krill Herbivorous zooplankton Phytoplankton Fig. 3-11, p. 48 7

Usable energy decreases with each link in a food chain or web There is less high-quality energy available to organisms at each succeeding feeding level because when chemical energy is transferred from one trophic level to the next, about 90% the energy is lost as heat Pyramid of Energy Flow Usable energy available at each trophic level (in kilocalories) Tertiary consumers 10 (human) Secondary consumers (perch) Primary consumers (zooplankton) Producers (phytoplankton) 100 1,000 10,000 Decomposers Some ecosystems produce plant matter faster than others do The rate of an ecosystem s producers converting energy into biomass is the gross primary productivity (GPP). Some of the biomass must be used for the producers own respiration. Net primary productivity (NPP) is the rate that producers use photosynthesis to store biomass minus the rate at which they use energy for aerobic respiration. NPP measures how fast producers can provide biomass needed by consumers in an ecosystem. Ecosystems and aquatic life zones differ in their NPP. The three most productive systems are swamps and marshes, tropical rain forests, and estuaries. The three least productive are tundra, desert scrub, and extreme desert. Fig. 3-12, p. 49 8

NPP in Major Life Zones and Ecosystems Terrestrial Ecosystems Swamps and marshes Tropical rain forest Temperate forest Northern coniferous forest (taiga) Savanna Agricultural land Woodland and shrubland Temperate grassland Tundra (arctic and alpine) Desert scrub Extreme desert Aquatic Ecosystems Estuaries Lakes and streams Continental shelf Open ocean Fig. 3-13, p. 49 Nutrients cycle within and among ecosystems Elements and compounds move through air, water, soil, rock and living organisms in biogeochemical, or nutrient, cycles. Section 3-4 WHAT HAPPENS TO MATTER IN AN ECOSYSTEM? 9

The water cycle Solar energy evaporates water; the water returns as precipitation (rain or snow), goes through organisms, goes into bodies of water, and evaporates again. Water is filtered and partly purified as it moves through the hydrological cycle. Water can be stored as ice in glaciers or in underground aquifers. The water cycle Unique properties of water include that it: Is held together by hydrogen bonds. Exists as a liquid over a wide temperate range. Stores a large amount of heat. Requires a large amount of energy to be evaporated. Dissolves a variety of compounds. Filter s some UV rays from the sun. Can move through capillary action. Expands when freezes. Exists in all three phases at the Earth s surface. The water cycle The Water Cycle Humans alter the water cycle in 3 ways: Withdrawing freshwater at faster rates than nature can replenish it. Clearing vegetation which increases runoff and decreases replenishment of groundwater supplies. Draining wetlands which interferes with flood control. 10

12/21/13 Condensation Condensation Ice and snow The carbon cycle Transpiration from plants Precipitati on to land Evaporation of surface water Carbon is the basic building block of carbohydrates, fats, proteins, DNA, and other compounds. Carbon circulates through the biosphere, hydrosphere, and atmosphere. Producers, consumers and decomposers circulate carbon in the biosphere. Fossil fuels contain carbon. Humans are altering atmospheric carbon dioxide mostly by our use of fossil fuels and our destruction of the carbon-absorbing vegetation. Evaporation from ocean Runoff Lakes and reservoirs Infiltration and percolation into aquifer Groundwat er in aquifers Runoff Increased runoff on land covered with crops, buildings and pavement Runoff Overpumpin g of aquifers Precipitati on to ocean Increased runoff from cutting forests and filling wetlands Water pollution Runoff Ocean Natural process Natural reservoir Human impacts Natural pathway Pathway affected by human activities Fig. 3-14, p. 51 Carbon dioxide in atmosphere The Carbon Cycle Respiration Photosynthesis Animals (consumers) Diffusion Burning fossil fuels Forest fires Plants (producers) Deforestation Transportation Carbon dioxide dissolved in ocean Respiration Carbon in animals (consumers) Carbon in plants (producer s) Decomposition Marine food webs Producers, consumers, decomposers Carbon in limestone or dolomite sediments Carbon in fossil fuels Compaction Process Reservoir Pathway affected by humans Natural pathway Fig. 3-15, p. 53 11

The nitrogen cycle: bacteria in action Nitrogen gas (N 2 ), which makes up 78% of the atmosphere, cannot be used directly by most living organisms. Nitrogen-fixing bacteria convert N 2 into compounds that are useful nutrients for plants and animals. The nitrogen cycle: bacteria in action The nitrogen cycle includes the following steps: Specialized bacteria convert gaseous nitrogen to ammonia in nitrogen fixation. Specialized bacteria convert ammonia in the soil to nitrite ions and nitrate ions; the latter is used by plants as a nutrient. This process is nitrification. Decomposer bacteria convert detritus into ammonia and water-soluble salts in ammonification. In denitrification, anaerobic bacteria in soggy soil and bottom sediments of water areas convert NH 3 and NH 4 + back into nitrite and nitrate ions, then into nitrogen gas and nitrous oxide gas, which are released into the atmosphere. The nitrogen cycle: bacteria in action The Nitrogen Cycle Human activities have more than doubled the annual release of nitrogen from the land into the rest of the environment, mostly from the greatly increased use of inorganic fertilizers to grow crops. This excessive input of nitrogen into the air and water contributes to pollution and other problems. 12

12/21/13 Process Denitrification by bacteria Nitrification by bacteria Nitrogen in atmosphere Reservoir Pathway affected by humanspathway Natural Nitrogen oxides from burning fuel and using inorganic fertilizers Electrical storms The phosphorus cycle Nitrogen in animals (consumers) Volcanic activity Nitrogen in plants (producers) Nitrates from fertilizer runoff and decompositio n Decomposition Uptake by plants Nitrate in soil Nitrogen loss to deep ocean sediments Nitrogen in ocean sediment s Bacteria Ammonia in soil Fig. 3-16, p. 54 Phosphorus circulates through water, Earth s crust, and living organisms in the phosphorus cycle. Phosphorus does not cycle through the atmosphere. The major reservoirs of phosphorus on Earth are rock formations and ocean bottom sediments. Phosphorus is transferred by food webs and is an important component of many biological molecules. Phosphorus is often the limiting factor for plant growth. Human activity removes phosphate from the earth to make fertilizer and reduces phosphate levels in tropical soils by clearing forests. Phosphate-rich runoff from the land can produce huge populations of algae, which can upset chemical cycling and other processes. Process The Phosphorus Cycle Reservoir Pathway affected by humans Natural pathway Phosphates in mining waste Phosphate s in sewage Phosphate s in fertilizer Runoff Runoff Sea birds Runoff Erosion Animals (consumers) Phosphate dissolved in water Plants (producers) Plate tectonic s Phosphate in rock (fossil bones, guano) Phosphate in shallow ocean sediments Ocean food webs Phosphate in deep ocean sediments Bacteria Fig. 3-17, p. 54 13

The sulfur cycle The Sulfur Cycle Much of the earth s sulfur is stored underground in rocks and minerals. Hydrogen sulfide (H 2 S) is released from volcanoes and anaerobic decomposition of organic matter in bogs and swamps. Humans have been increasing atmospheric sulfur dioxide by burning sulfur-containing fuels, refining sulfur-containing fuels, and converting sulfur containing metallic mineral ores into free metals. Sulfur dioxide in atmosphere Dimethy l Sulfide a bacteria byprodu ct Sulfur in ocean sedimen ts Process Reservoir Pathway affected by humans Natural pathway Smelting Burning Refining coal fossil fuels Mining and extraction Sulfur in animals (consumers ) Decay Sulfur in plants (producers) Decay Uptake by plants Sulfur in soil, rock and fossil fuels Sulfuric acid and Sulfate deposited as acid rain Fig. 3-18, p.56 Section 3-5 HOW DO SCIENTISTS STUDY ECOSYSTEMS? 14

Some scientists study nature directly Field research ( muddy-boots biology ) involves making direct measurements and observations of ecosystems in natural settings. Remote sensing devices can gather data on the earth s surface that can be converted into usable forms by geographic information systems (GIS), such as computerized maps of an area that are used to examine forest cover, water resources, air pollution emissions, coastal changes, and changes in global sea temperatures. Some scientists study ecosystems in the laboratory Ecologists use tanks, greenhouses, and controlled indoor and outdoor chambers to study ecosystems in laboratory research. This allows control of light, temperature, CO 2, humidity, and other variables. We need to learn more about the health of the world s ecosystems Mathematical models and computer simulations can help scientists understand large and very complex systems. Simulations are no better than the data and assumptions used to develop models. We need more baseline data about components and physical and chemical conditions in order to determine how well the ecosystem is functioning and anticipate how best to prevent harmful environmental changes. Three Big Ideas Life is sustained by the flow of energy from the sun through the biosphere, the cycling of nutrients within the biosphere, and gravity. Some organisms produce the nutrients they need, some survive by consuming other organisms, and others recycle nutrients back to producers. Human activities are altering the flow of energy through food chains and webs, and the cycling of nutrients within ecosystems and the biosphere. 15