Chapter 3 Ecosystems: What Are They and How Do They Work?

THE NATURE OF ECOLOGY  Ecology is a study of connections in nature. How organisms interact with one another and with their nonliving environment. How organisms interact with one another and with their nonliving environment. Figure 3-2

Important Ecological Terms  Organism  Cell  Eukaryote  Prokaryote  Species  Asexual Reproduction  Sexual Reproduction

Organisms and Species  Organisms  Populations  Communities  Ecosystems  Biosphere Figure 3-3

Fig. 3-3, p. 52 Insects 751,000 Other animals 281,000 Fungi 69,000 Prokaryotes 4,800 Plants 248,400 Protists 57,700 Known species 1,412,000

Populations  Genetic diversity In most natural populations individuals vary slightly in their genetic makeup. In most natural populations individuals vary slightly in their genetic makeup. Figure 3-5

Fig. 3-6, p. 54 Lithosphere (crust, top of upper mantle) Rock Soil Vegetation and animals Atmosphere Oceanic Crust Continental Crust Lithosphere Upper mantle Asthenosphere Lower mantle Mantle Core Biosphere Crust Crust (soil and rock) Biosphere (living and dead organisms) Hydrosphere (water) Atmosphere (air)

Earth’s Life-Support Systems  Atmosphere Contains troposphere (inner layer - 11 miles above sea level - weather) & stratosphere (ozone layer). Contains troposphere (inner layer - 11 miles above sea level - weather) & stratosphere (ozone layer).  Hydrosphere All the earth’s water: liquid, ice, water vapor All the earth’s water: liquid, ice, water vapor  Lithosphere The earth’s crust and upper mantle. The earth’s crust and upper mantle.

What Sustains Life on Earth?  Solar energy  Cycling of matter  Gravity Figure 3-7

What Happens to Solar Energy Reaching the Earth?  Solar energy flowing through the biosphere warms the atmosphere, evaporates and recycles water, generates winds and supports plant growth. Figure 3-8

ECOSYSTEM COMPONENTS  Biomes (terrestrial & aquatic)  Climate vs. weather  Range of tolerance Figure 3-9

Nonliving and Living Components of Ecosystems  Abiotic vs. biotic components  Ecotones (edge effect) Figure 3-10

Factors That Limit Population Growth  Law of tolerance  Limiting factors Figure 3-11

Factors That Limit Population Growth  The physical conditions of the environment can limit the distribution of a species. Figure 3-12

Biotic components of ecosystems  Producers  Consumers  Decomposers  Herbivores (prim. Consumer)  Carnivores (primary, secondary, tertiary)  Omnivore  Detritivore  Scavenger

Producers: Basic Source of All Food  Chemosynthesis: Some organisms such as deep ocean bacteria draw energy from hydrothermal vents and produce carbohydrates from hydrogen sulfide (H 2 S) gas. Some organisms such as deep ocean bacteria draw energy from hydrothermal vents and produce carbohydrates from hydrogen sulfide (H 2 S) gas.

Photosynthesis: A Closer Look  Chlorophyll molecules in the chloroplasts of plant cells absorb solar energy.  This initiates a complex series of chemical reactions in which carbon dioxide and water are converted to sugars and oxygen. Figure 3-A

Decomposers and Detritivores Decomposers: Recycle nutrients in ecosystems. Decomposers: Recycle nutrients in ecosystems. Detritivores: Insects or other scavengers that feed on wastes or dead bodies. Detritivores: Insects or other scavengers that feed on wastes or dead bodies. Figure 3-13

Aerobic and Anaerobic Respiration: Getting Energy for Survival  Aerobic Respiration: The opposite of photosynthesis The opposite of photosynthesis

Aerobic and Anaerobic Respiration: Getting Energy for Survival  Anaerobic respiration or fermentation: In the absence of oxygen. In the absence of oxygen. The end products vary based on the chemical reaction: The end products vary based on the chemical reaction: Methane gasMethane gas Ethyl alcoholEthyl alcohol Acetic acidAcetic acid Hydrogen sulfideHydrogen sulfide

Two Secrets of Survival: Energy Flow and Matter Recycle  An ecosystem survives by a combination of energy flow and matter recycling. Figure 3-14

BIODIVERSITY Figure 3-15

Biodiversity Loss and Species Extinction: Remember HIPPO  H for habitat destruction and degradation  I for invasive species  P for pollution  P for human population growth  O for overexploitation

Why Should We Care About Biodiversity?  Biodiversity provides us with: Natural Resources (food water, wood, energy, and medicines) Natural Resources (food water, wood, energy, and medicines) Natural Services (air and water purification, soil fertility, waste disposal, pest control) Natural Services (air and water purification, soil fertility, waste disposal, pest control) Aesthetic pleasure Aesthetic pleasure

ENERGY FLOW IN ECOSYSTEMS  Food chains  Food webs Figure 3-17

Food Webs  Trophic levels are interconnected within a more complicated food web. Figure 3-18

Energy Flow in an Ecosystem: Losing Energy in Food Chains and Webs  2 nd law of thermodynamics - there is a decrease in the amount of energy available to each succeeding organism in a food chain or web.  10% Rule  Rarely have more than 4-5 trophic levels

Energy Flow in an Ecosystem: Losing Energy in Food Chains and Webs  Ecological efficiency: percentage of useable energy transferred as biomass from one trophic level to the next. Figure 3-19

Productivity of Producers: The Rate Is Crucial  Gross primary production (GPP) Rate at which an ecosystem’s producers convert solar energy into chemical energy as biomass. Rate at which an ecosystem’s producers convert solar energy into chemical energy as biomass. Figure 3-20

Net Primary Production (NPP)  NPP = GPP – R Rate at which producers use photosynthesis to store energy minus the rate at which they use some of this energy through respiration (R). Rate at which producers use photosynthesis to store energy minus the rate at which they use some of this energy through respiration (R). Figure 3-21

 What are nature’s three most productive and three least productive systems? Figure 3-22

MATTER CYCLING IN ECOSYSTEMS  Nutrient Cycles: Global Recycling Biogeochemical cycles move substances through air, water, soil, rock and living organisms. Biogeochemical cycles move substances through air, water, soil, rock and living organisms. Hydrologic cycle (water) Hydrologic cycle (water) Atmosphereic cycles (C, N) Atmosphereic cycles (C, N) Sedimentary cycles (P, S) Sedimentary cycles (P, S)

The Water Cycle Figure 3-26

Effects of Human Activities on Water Cycle  We alter the water cycle by: Withdrawing large amounts of freshwater. Withdrawing large amounts of freshwater. Clearing vegetation and eroding soils. Clearing vegetation and eroding soils. Polluting surface and underground water. Polluting surface and underground water. Contributing to climate change. Contributing to climate change.

The Carbon Cycle: Part of Nature’s Thermostat Figure 3-27

Effects of Human Activities on Carbon Cycle  We alter the carbon cycle by adding excess CO 2 to the atmosphere through: Burning fossil fuels. Burning fossil fuels. Clearing vegetation faster than it is replaced. Clearing vegetation faster than it is replaced. Figure 3-28

The Nitrogen Cycle: Bacteria in Action Figure 3-29

Effects of Human Activities on the Nitrogen Cycle  We alter the nitrogen cycle by: Adding gases that contribute to acid rain. Adding gases that contribute to acid rain. Adding nitrous oxide to the atmosphere through farming practices which can warm the atmosphere and deplete ozone. Adding nitrous oxide to the atmosphere through farming practices which can warm the atmosphere and deplete ozone. Contaminating ground water from nitrate ions in inorganic fertilizers. Contaminating ground water from nitrate ions in inorganic fertilizers. Releasing nitrogen into the troposphere through deforestation. Releasing nitrogen into the troposphere through deforestation.

Effects of Human Activities on the Nitrogen Cycle  Human activities such as production of fertilizers now fix more nitrogen than all natural sources combined. Figure 3-30

The Phosphorous Cycle Figure 3-31

Effects of Human Activities on the Phosphorous Cycle  We remove large amounts of phosphate from the earth to make fertilizer.  We reduce phosphorous in tropical soils by clearing forests.  We add excess phosphates to aquatic systems from runoff of animal wastes and fertilizers.

The Sulfur Cycle Figure 3-32

Effects of Human Activities on the Sulfur Cycle  We add sulfur dioxide to the atmosphere by: Burning coal and oil Burning coal and oil Refining sulfur containing petroleum. Refining sulfur containing petroleum. Convert sulfur-containing metallic ores into free metals such as copper, lead, and zinc releasing sulfur dioxide into the environment. Convert sulfur-containing metallic ores into free metals such as copper, lead, and zinc releasing sulfur dioxide into the environment.

The Gaia Hypothesis: Is the Earth Alive?  Some have proposed that the earth’s various forms of life control or at least influence its chemical cycles and other earth-sustaining processes. The strong Gaia hypothesis: life controls the earth’s life-sustaining processes. The strong Gaia hypothesis: life controls the earth’s life-sustaining processes. The weak Gaia hypothesis: life influences the earth’s life-sustaining processes. The weak Gaia hypothesis: life influences the earth’s life-sustaining processes.

HOW DO ECOLOGISTS LEARN ABOUT ECOSYSTEMS?  Geographic Information Systems & Remote Sensing  Ecologists also use controlled indoor and outdoor chambers to study ecosystems

Geographic Information Systems (GIS)  A GIS organizes, stores, and analyzes complex data collected over broad geographic areas.  Allows the simultaneous overlay of many layers of data. Figure 3-33