Ecosystems: What Are They and How Do They Work Chapter 3 (Miller and Spoolman, 2010)
Core Case Study: Tropical Rain Forests Are Disappearing • Cover about 2% of the earth’s land surface • Contain about 50% of the world’s known plant and animal species • At least half have been destroyed. • W/o strong conservation measures, most will be gone or severely degraded in your lifetime. • Disruption will have three major harmful effects • Reduce biodiversity • Accelerate global warming • Change regional weather patterns • Once a tipping point is reached, tropical rainforests will become less diverse tropical grasslands
Figure 3-1 Natural capital degradation: satellite image of the loss of tropical rainforest, cleared for farming, cattle grazing, and settlements, near the Bolivian city of Santa Cruz between June 1975 (left) and May 2003 (right).
3-1 What Keeps Us and Other Organisms Alive? • Concept 3-1Life is sustained by the flow of energy from the sun through the biosphere, the cycling of nutrients within the biosphere, and gravity.
Atmosphere • Thin envelope of air around the planet • Troposphere • extends about 17 km above sea level, contains nitrogen (78%), oxygen (21%), and is where weather occurs • Stratosphere • 17-48 km above sea level, lower portions contains enough ozone (O3) to filter out most of the sun’s ultraviolet radiation
Crust • Outermost, thin silicate zone, eight elements make up 98.5% of the weight of the earth’s crust Geosphere The Earth contains several layers or concentric spheres Upper portion contains nonrenewable fossil fuels and minerals that we use as well as renewable soil
Mantle • Largestzone, rich with iron, silicon, oxygen, and magnesium, very hot • Core • Innermost zone, mostly iron, solid inner part, surrounded by a liquid core of molten material • Extremely hot and dense Geosphere
Hydrosphere Consists of the earth’s liquid water, ice, and water vapor in the atmosphere
The Earth’s Life-Support System Has Four Major Components (2) • Biosphere – parts of the atmosphere, hydrosphere and geosphere where life exists. • From about 9 km (6 mi) above surface to bottom of the oceans.
Figure 3.6Natural capital: general structure of the earth showing that it consists of a land sphere, air sphere, water sphere, and life sphere.
Life Exists on Land and in Water • Biomes – large regions such as forests, deserts, and grasslands with distinct climates and certain species (especially vegetation) adapted to them. • Aquatic life zones – divisions of the watery parts of the biosphere each containing numerous ecosystems. • Freshwater life zones • Lakes and streams • Marine life zones • Coral reefs • Estuaries • Deep ocean
Figure 3.7Major biomes found along the 39th parallel across the United States. The differences reflect changes in climate, mainly differences in average annual precipitation and temperature.
Three Factors Sustain Life on Earth • One-way flow of high-quality energy beginning with the sun • Cycling of matter or nutrients • Gravity • Holds on to the atmosphere and enables the movement and cycling of chemicals through the air, water, soil, and organisms.
What Happens to Solar Energy Reaching the Earth? • UV, visible, and IR energy • Much is reflected by the atmosphere, only 1 % reaches surface • Lights the earth during the day, warms the air, evaporates and cycles water through the biosphere. • 1 % generates the wind, and only 0.1 % is harnessed by photosynthetic organisms. • Radiation • Absorbed by ozone , including 95 % of harmful UV • Absorbed by the earth • Reflected by the earth • Radiated by the atmosphere as heat • Natural greenhouse effect • Carbon dioxide, methane (CH4), nitrous oxide (N2O), and ozone (O3) • Human activities are increasing these gases.
Sun and Solar Energy Fireball of hydrogen (72%) and helium (28%) Nuclear fusion Sun has existed for 6 billion years Sun will stay for another 6.5 billion years Emits visible light, UV radiation, heat (infrared radiation) <0.1% of solar energy is captured by green plants and bacteria Powers the cycling of matter and weather system Distributes heat and fresh water
Natural Greenhouse Effect ~50% of sun’s radiation scattered/reflected Some radiation is lost to space Some radiation absorbed by greenhouse gasses This heat radiates back into space Greenhouse gases reradiate stored energy back toward earth Heats up lower atmosphere The rest is absorbed into earth
Natural Greenhouse Effect • Similar effect as glass on a greenhouse or windows on a car • Keeps Earth warm enough to sustain life! • Earth would be 18°C (33°F) colder • Greenhouse gases • Water vapor • CO2 • Methane • Nitrous oxide • (Ozone)
What happens if we add greenhouse gases? More radiation trapped More heat reradiated back towards earth Temperature increases
3-3 What Are the Major Components of an Ecosystem? • Concept 3-3A Ecosystems contain living (biotic) and nonliving (abiotic) components. • Concept 3-3B Some organisms produce the nutrients they need, others get their nutrients by consuming other organisms, and some recycle nutrients back to producers by decomposing the wastes and remains of organisms.
Ecosystems Have Living and Nonliving Components (1) • Abiotic • Water • Air • Nutrients • Rocks • Heat • Solar energy • Biotic • Living and once living biological components—plants animals and microbes. • Dead organisms, dead part of organisms, and waste products of organisms.
Figure 3.9Major living (biotic) and nonliving (abiotic) components of an ecosystem in a field.
Ecosystems Have Living and Nonliving Components(2) • Different species AND their populations thrive under different physical and chemical conditions. • Some need bright light, or warmer temperatures, or higher humidity or pH, for example, than others. • Each population in an ecosystem has a range of tolerance to variations in the physical and chemical environment. • Likewise individuals in population can vary in their tolerance to environmental factors because of small differences in genetic makeup(i.e. genetic variation).
Figure 3.10Range of tolerance for a population of organisms, such as fish, to an abiotic environmental factor—in this case, temperature. These restrictions keep particular species from taking over an ecosystem by keeping their population size in check. Question: Which scientific principle of sustainability (see back cover) is related to the range of tolerance concept?
Several Abiotic Factors Can Limit Population Growth • Limiting factor – specific factor(s) important in regulating the growth of a population. • Terrestrial ecosytems: precipitation, soil nutrients, temperature • Aquatic ecosystems: temperature, sunlight, nutrients, DO, and salinity. • Limiting factor principle • Too much or too little of any abiotic factor can limit or prevent growth of a population, even if all other factors are at or near the optimal range of tolerance • One way in which population control (one of the scientific principles of sustainability) is achieved
Producers and Consumers Are the Living Components of Ecosystems (1) • Trophic level • Producers, or autotrophs • Photoautotrophs: plants, algae, aquatic plants, and phytoplankton, • Photosynthesis • Chemoautotrophs: mostly specialized bacteria • Chemosynthesis (see p. 59 for details) • Consumers, or heterotrophs • Primary • Secondary • Third and higher level • Omnivores • Decomposers • Primarily bacteria and fungi • Detritus feeders, or detritivores • Mites, earthworms, some insects, catfish, and larger scavengers like vultures.
Figure 3.11Various detritivores and decomposers (mostly fungi and bacteria) can “feed on” or digest parts of a log and eventually convert its complex organic chemicals into simpler inorganic nutrients that can be taken up by producers.
Producers and Consumers Are the Living Components of Ecosystems (2) • Organisms use the chemical energy stored in glucose and other organic compounds to fuel their life processes. • In most cells, energy released by aerobic respiration. • Though the steps differ, the net chemical rxn is essentially the opposite of that for photosynthesis. • Anaerobic respiration, or fermentation • End products include CH4, ethyl alcohol (C2H6O), acetic acid (C2H4O2), or hydrogen sulfide (H2S).
Energy Flow and Nutrient Cycling Sustain Ecosystems and the Biosphere • Ecosystems and the biosphere are sustained through a combination of one-way energy flow from the sun through these systems and nutrient cycling of key materials within them. • These two principles of sustainability (see back cover of textbook) arise from • Structure and function of natural ecosystems • Law of conservation of matter, and • Two law of thermodynamics.
Figure 3.12Natural capital: the main structural components of an ecosystem (energy, chemicals, and organisms). Nutrient cycling and the flow of energy—first from the sun, then through organisms, and finally into the environment as low-quality heat—link these components.
Science Focus: Many of the World’s Most Important Species Are Invisible to Us • Microorganisms, or microbes, are a vital part of earth’s natural capital. Explain. • Bacteria • Protozoa • Fungi • Phytoplankton
3-4 What Happens to Energy in an Ecosystem? • Concept 3-4A Energy flows through ecosystems in food chains and webs. • Concept 3-4B As energy flows through ecosystems in food chains and webs, the amount of chemical energy available to organisms at each succeeding feeding level decreases.
Energy Flows Through Ecosystems in Food Chains and Food Webs • Chemical energy stored as nutrients in the bodies and wastes of organisms flows through ecosystems from one trophic level (feeding level) to another. • Food chain – a sequence of organisms, each of which serves as a source of food or energy for the next. • Primarily through photosynthesis, feeding and decomposition. • Food web – complex network of interconnected food chains.
Figure 3.13A food chain. The arrows show how chemical energy in nutrients flows through various trophic levels in energy transfers; most of the energy is degraded to heat, in accordance with the second law of thermodynamics. Question: Think about what you ate for breakfast. At what level or levels on a food chain were you eating?
Figure 3.14Greatly simplified food web in the Antarctic. Many more participants in the web, including an array of decomposer and detritus feeder organisms, are not depicted here. Question: Can you imagine a food web of which you are a part? Try drawing a simple diagram of it.
Usable Energy Decreases with Each Link in a Food Chain or Web • Biomass – the dry weight of all organic matter contained in its organisms. • Chemical energy stored in biomass is transferred up the food web. • Inefficient. Decrease in energy available at each succeeding trophic level. • Ecological efficiency – percentage of usable chemical energy transferred as biomass from one trophic level to the next. • Ranges from 2 to 40 %, but 10 % is average.
Figure 3.15Generalized pyramid of energy flow showing the decrease in usable chemical energy available at each succeeding trophic level in a food chain or web. In nature, ecological efficiency varies from 2% to 40%, with 10% efficiency being common. This model assumes a 10% ecological efficiency (90% loss of usable energy to the environment, in the form of low-quality heat) with each transfer from one trophic level to another. Question: Why is a vegetarian diet more energy efficient than a meat-based diet?
Some Ecosystems Produce Plant Matter Faster Than Others Do (1) • Ultimately, the biomass of an ecosystem depends on the amount of energy captured and stored by producers. • Gross primary productivity (GPP) – the rate at which an ecosystems producers convert solar energy into chemical energy. • Usually measured in energy production per unit area per unit time, e.g. kcal/m2/yr. • To stay alive producers must use some of this stored chemical energy for their own respiration.
Some Ecosystems Produce Plant Matter Faster Than Others Do (2) • Net primary productivity – rate at which producers use photosynthesis to produce and store energy minus the rate at which they use this stored energy for aerobic respiration. • Ecosystems and aquatic life zones differ in their NPP (Fig. 3-16). • Decreases from equator to pole. • Estuaries are high • Upwellings (water moving up from depths to surface) • Open ocean, low NPP, but high absolute amount. Why?
Figure 3.16Estimated annual average net primary productivity in major life zones and ecosystems, expressed as kilocalories of energy produced per square meter per year (kcal/m2/yr). Question: What are nature’s three most productive and three least productive systems? (Data from R. H. Whittaker, Communities and Ecosystems, 2nd ed., New York: Macmillan, 1975)
Some Ecosystems Produce Plant Matter Faster Than Others Do (3) • Should be clear that the planet’s NPP ultimately limits the number of consumers (including humans) that can survive on the earth. • Ecologists estimated that humans use, waste, or destroy about 20-32% of the earth’s total potential NPP. • Remarkable considering that humans make up on 1% of the total biomass of all of the earth’s consumers.
3-5 What Happens to Matter in an Ecosystem? • Concept 3-5 Matter, in the form of nutrients, cycles within and among ecosystems and the biosphere, and human activities are altering these chemical cycles.
Nutrients Cycle in the Biosphere • Biogeochemical cycles, or nutrient cycles – the cycling of elements and compounds through air, water, soil, rock, and living organisms in ecosystems and in the biosphere. • Driven directly and indirectly by the sun and gravity. • Human activities are altering them. • Include: Hydrologic, Carbon, Nitrogen, Phosphorus, and Sulfur Cycles. • Atoms and compounds moving in this cycle may accumulate in one portion of the cycle indefinitely. These atmospheric, oceanic, and underground deposits are called reservoirs. • Connect past, present , and future forms of life
Water Cycles through the Biosphere • The hydrologic cycle, or water cycle, collects, purifies, and distributes the earth’s fixed supply of water. • Powered by energy from the sun, involves three major processes: • Evaporation • 84% of water in atmosphere comes from the ocean. • Precipitation • Surface runoff, infiltration, and percolation to aquifers • Transpiration • On land, 90% of water reaches atmosphere from plants. • Alteration of the hydrologic cycle by humans • Withdrawal of large amounts of freshwater at rates faster than nature can replace it • Clearing vegetation • Increased flooding when wetlands are drained
Figure 3.17Natural capital: simplified model of the hydrologic cycle with major harmful impacts of human activities shown in red. See an animation based on this figure at CengageNOW. Question: What are three ways in which your lifestyle directly or indirectly affects the hydrologic cycle?
Science Focus: Water’s Unique Properties • Properties of water due to hydrogen bonds between water molecules: • Exists as a liquid over a large range of temperature • Changes temperature slowly (High heat capacity) • High boiling point: 100˚C • Takes lots of energy to evaporate (High heat of vaporization) • Adhesion and cohesion • Expands as it freezes • Solvent • Filters out harmful UV
Carbon Cycle Depends on Photosynthesis and Respiration • Carbon cycle – carbon circulates through the biosphere, the atmosphere, and parts of the hydrosphere. • Based on CO2, which make up 0.038% of atmosphere. • Link between photosynthesis in producers and aerobic respiration in producers, consumers, and decomposers. • Key component of earth’s thermostat (a GHG). • Additional CO2 added to the atmosphere • Tree clearing • Burning of fossil fuels • Computer models suggest that it is very likely (90-99% probability) that human activities are enhancing the green house effect.