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

2. 3-1 What Is Ecology?
Concept 3-1 Ecology is the study of how organisms interact with one another and with their physical environment of matter and energy.

3. 3-1 What Is Ecology? Ecology is a study of connections in nature.
How organisms interact with one another and with their nonliving environment.

4. Species Make Up the Encyclopedia of Life
Organisms – individual forms of life
Classified into species based on certain characteristics
Species – a set of individuals that can mate and produce viable, fertile offspring
1.75 Million species identified
Up to 10–14 million species not yet identified??
Insects make up most of the known species

5. Science Focus: Have You Thanked the Insects Today?
Many times we classify insects as pests:
Compete with us for food
Spread human diseases
Bite or sting us
Can be a nuisance
However, they are VERY beneficial:
Pollinators
Eat other insects
Loosen and renew soil
Estimated $57 billion/yr in ecological services

6. Species Make Up the Encyclopedia of Life
A population is a group of interacting individuals of the same species occupying a specific area.
The space an individual or population normally occupies is its habitat.

7. Species Make Up the Encyclopedia of Life
Genetic diversity
In most natural populations individuals vary slightly in their genetic makeup.
These genetic diversity is crucial to the survival of the population.

8. Levels of Organization of Matter in Nature
Populations of different species living and interacting in an area form a community.
A community interacting with its physical environment of matter and energy is an ecosystem.
The biosphere is where all of the Earth’s life is found
A “global ecosystem”

9. 3-2 What Keeps Us and Other Organisms Alive?
Concept 3-2 Life is sustained by the flow of energy from the sun through the biosphere, the cycling of nutrients within the biosphere, and gravity.

10. Natural Capital: General Structure of the Earth
The biosphere consists of several physical layers that contain:
Air
Water
Soil
Minerals
Life

11. The Earth’s Life-Support System Has Four Major Components
Biosphere – All of the life on the planet
Atmosphere – Membrane of air around the planet.
Troposphere – lowest layer - most gas of any layer
where weather occurs
Stratosphere – contains ozone to filter out most of the sun’s harmful UV radiation.
Hydrosphere – All the earth’s water: liquid, ice, water vapor
Geosphere – The earth’s crust and upper mantle
Lithosphere – hard outer crust
Asthenosphere – molten interior

12. Three Factors Sustain Life on Earth
One-way flow of energy beginning with the sun
Follows the laws of thermodynamics
Most is lost as heat
Cycling of matter or nutrients
Nutrients exist in a fixed amount
Follows the law of conservation of matter
Gravity

13. Flow of Energy to and from the Earth
Solar energy flowing through the biosphere warms the atmosphere, evaporates and recycles water, generates winds and supports plant growth.
Natural greenhouse effect – natural process that keeps the Earth warmer than it would otherwise be

14. Life Exists on Land and in Water
Life exists on land systems called biomes and in freshwater and ocean aquatic life zones.

15. 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.

16. Ecosystems Have Living and Nonliving Components
Ecosystems consist of living (biotic) and nonliving (abiotic) components.
Biotic or Abiotic?
Plants
Water
Animals
Temperature
Rocks/Minerals
Bacteria
Solar Energy
Landforms
Soil

17. Several Abiotic Factors Can Limit Population Growth
Populations have a range of tolerance to variations in their physical and chemical environments.

18. Several Abiotic Factors Can Limit Population Growth
Availability of matter and energy resources can limit the number of organisms in a population.
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

19. Several Abiotic Factors Can Limit Population Growth
The physical conditions of the environment can limit the distribution (range) of a species.

20. Producers and Consumers Are the Living Components of Ecosystems
Producers, or autotrophs, make their own food from nutrients/energy obtained from the environment
Most producers capture sunlight to produce carbohydrates by photosynthesis:
** You must memorize this equation if you haven’t already. It will come up throughout the year.

21. Photosynthesis
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.

22. Producers and Consumers Are the Living Components of Ecosystems
Some organisms can obtain energy from inorganic compounds in their environment WITHOUT sunlight through a process called chemosynthesis.
Deep ocean bacteria draw energy from hydrothermal vents and produce carbohydrates from hydrogen sulfide (H2S) gas.

23. Producers and Consumers Are the Living Components of Ecosystems
Consumers, or heterotroph, cannot produce their own food and, therefore, must obtain their nutrients by feeding on other organisms.
Herbivores
Primary consumers that eat producers
Carnivores
Secondary consumers eat primary consumers
Third- and higher-level consumers: carnivores that eat carnivores
Omnivores
Feed on both plant and animals

24. Producers and Consumers Are the Living Components of Ecosystems
Detritivores: Insects or other scavengers that feed on wastes or dead bodies (detritus) – physically break down
Decomposers: Bacteria and/or fungi that use enzymes to recycle nutrients in ecosystems – chemically break down

25. Producers and Consumers Are the Living Components of Ecosystems
Organisms break down carbohydrates and other organic compounds in their cells to obtain the energy they need.
This is usually done through aerobic respiration.
Aerobic means “with oxygen”
** You must memorize this equation if you haven’t already. It will come up throughout the year.

26. Producers and Consumers Are the Living Components of Ecosystems
Some decomposers get energy by breaking down glucose (or other organic compounds) WITHOUT oxygen through a process called anaerobic respiration, or fermentation
Anaerobic means “without oxygen”
The end products vary based on the chemical reaction:
Methane gas
Ethyl alcohol
Acetic acid
Hydrogen sulfide

27. Energy Flow and Nutrient Cycling Sustain Ecosystems and the Biosphere
An ecosystem is sustained by a combination of a one-way flow of energy and the cycling of key nutrients.

28. Science Focus: Many of the World’s Most Important Species Are Invisible to Us
Multitudes of tiny microbes such as bacteria, protozoa, fungi, and yeast help keep us alive.
Harmful microbes are the minority
Soil bacteria (nitrogen fixing bacteria) convert nitrogen gas to a usable form for plants
They help produce foods: bread, cheese, yogurt, beer, wine
Make up 90% of all living mass on Earth
Help purify water, provide oxygen, breakdown waste
Live beneficially in your body (intestines, nose)

29. 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.

30. Energy Flows Through Ecosystems in Food Chains and Food Webs
Food chains and webs show how eaters, the eaten, and the decomposed are connected to one another in an ecosystem.
The arrows point in the direction of the energy flow.

31. Energy Flows Through Ecosystems in Food Chains and Food Webs
A food web shows the connections of all organisms within an ecosystem.

32. Usable Energy Decreases with Each Link in a Food Chain or Web
Biomass – the dry weight of all organic matter contained in an organism(s).
Chemical energy in biomass is transferred from one trophic level to another.

33. Pyramid of Energy Flow
Ecological efficiency: percentage of useable energy transferred as biomass from one trophic level to the next.
Typically, only 10% efficient (90% lost as heat)

34. Usable Energy Decreases with Each Link in a Food Chain or Web
Food chains rarely have more than 4 steps or 3 trophic levels. Why?

35. Usable Energy Decreases with Each Link in a Food Chain or Web
In accordance with the 2nd law of thermodynamics, there is a decrease in the amount of energy available to each succeeding organism in a food chain or web.
Cellular respiration - the breakdown of glucose to release energy – is only 38% efficient
Energy is lost as heat
Energy is also used for growth, reproduction, movement
Ultimately, only about 10% of the original energy is available for the next trophic level (90% lost as heat)

36. Some Ecosystems Produce Plant Matter Faster Than Others Do
Gross primary production (GPP)
Rate at which an ecosystem’s producers convert solar energy into chemical energy (photosynthesis) as biomass.

37. Some Ecosystems Produce Plant Matter Faster Than Others Do
Net Primary Production (NPP)
Rate at which producers use photosynthesis to store energy minus the rate at which they use some of this energy through respiration (R).
NPP = GPP – R

38. Estimated Annual Average NPP in Major Life Zones and Ecosystems
What are nature’s most productive/least productive systems?

39. Info from notes handout
Sample food chain

40. Info from notes handout
Pyramid of Numbers
Pyramid of Biomass
Pyramid of Energy

41. 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.

42. Nutrients Cycle in the Biosphere
Biogeochemical Cycles recycle nutrients through the earth’s air, land, water, and living organisms.
Nutrients are the elements and compounds that organisms need to live, grow, and reproduce.
Biogeochemical cycles move these substances through air, water, soil, rock and living organisms.
Connect past, present , and future forms of life 42

43. The Water Cycle

44. The Water Cycle 44

45. Effects of Human Activities on Water Cycle
Humans alter the water cycle by:
Withdrawal of large amounts of freshwater at rates faster than nature can replace it
Clearing vegetation and eroding soils.
Increased flooding when wetlands are drained
Polluting surface and underground water.
Contributing to climate change.
Increases melting, evaporation, precipitation, etc. 45

46. The Carbon Cycle 46

47. The Carbon Cycle

48. Effects of Human Activities on Carbon Cycle
Humans alter the carbon cycle by adding excess CO2 to the atmosphere through:
Burning fossil fuels
Clearing/burning vegetation faster than it is replaced 48

49. The Nitrogen Cycle 49

50. The Nitrogen Cycle

51. Nitrogen Cycles through the Biosphere: Bacteria in Action
Nitrogen fixation – converting atmospheric N2 into ammonia (NH3) or ammonium (NH4) that can be used by plants
Lightning – ammonia falls to the ground with the rain
Nitrogen-fixing bacteria
Nitrification – Nitrifying bacteria convert ammonium (NH4) to nitrates (NO3) and/or nitrites (NO2)
Denitrification – Denitrifying bacteria convert ammonia, nitrates, or nitrites back into atmospheric N2.
Ammonification – Decomposers convert ditritus into ammonia or ammonium.

52. Nitrogen Fixation:
A Closer Look

53. Effects of Human Activities on the Nitrogen Cycle
Humans alter the nitrogen cycle by:
Adding gases that contribute to acid rain
NO and N2O
Contaminating bodies of water with excess nitrates from inorganic fertilizers
Humans fix more nitrogen than all natural sources combined
Adding nitrogen to the troposphere through deforestation
Remove nitrogen from topsoil 53

54. The Phosphorous Cycle

55. The Phosphorous Cycle 55

56. Effects of Human Activities on the Phosphorous Cycle
Cycles through water, the earth’s crust, and living organisms (NOT the atmosphere like the others)
May be limiting factor for plant growth
Humans alter the phosphorus cycle by:
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. 56

57. The Sulfur Cycle 57

58. The Sulfur Cycle

59. Effects of Human Activities on the Sulfur Cycle
Sulfur found in organisms, ocean sediments, soil, rocks, and fossil fuels.
Sulfur dioxide (SO2) in the atmosphere
Humans alter the sulfur cycle by adding sulfur dioxide to the atmosphere through:
Burning sulfur-containing coal and oil
Refining sulfur-containing petroleum
Smelting sulfur-containing metallic mineral ores
These can all lead to acid rain
Sulfuric acid (H2SO4) when SO4 mixes with H2O 59