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

2. Core Case Study: Have You Thanked the Insects Today?
Many plant species depend on insects for pollination.
Insect can control other pest insects by eating them
Figure 3-1

3. Core Case Study: Have You Thanked the Insects Today?
…if all insects disappeared, humanity probably could not last more than a few months [E.O. Wilson, Biodiversity expert].
Insect’s role in nature is part of the larger biological community in which they live.

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

5. Ecology
Ecology: the study of the relationships between organisms & the abiotic (nonliving) and biotic (living) environment.
The physical conditions influence the habitat in which an organism lives. These include:
substrate
humidity
sunlight
temperature
salinity
pH (acidity)
exposure
altitude
depth
Each abiotic (or physical) factor may be well suited to the organism or it may present it with problems to overcome. O2
Nutrients
CO2
Relationships involve interactions with the physical world as well as interrelationships with other species and individuals of the same species.

6. Biosphere Ecosystems Realm of ecology Communities Populations
Universe
Galaxies
Biosphere
Solar systems
Planets
Earth
Biosphere
Ecosystems
Ecosystems
Communities
Populations
Realm of ecology
Organisms
Communities
Organ systems
Organs
Figure 3.2
Natural capital: levels of organization of matter in nature. Ecology focuses on five of these levels.
Tissues
Cells
Populations
Protoplasm
Molecules
Atoms
Organisms
Subatomic Particles
Fig. 3-2, p. 51

7. Biological Complexity
Living organisms can be studied at different levels of complexity.
From least to most complex, these levels are (in an ecological context):
Individual
Population
Community
Ecosystem
Biome
Biosphere
Biosphere
Biome
Ecosystem
Community
Population
Individual

8. Organisms and Species
Organisms, the different forms of life on earth, can be classified into different species based on certain characteristics.
Figure 3-3

9. Other animals 281,000 Known species 1,412,000 Insects 751,000 Fungi
69,000
Prokaryotes
4,800
Figure 3.3
Natural capital: breakdown of the earth’s 1.4 million known species. Scientists estimate that there are 4 million to 100 million species.
Plants
248,400
Protists
57,700
Fig. 3-3, p. 52

10. Case Study: Which Species Run the World?
Multitudes of tiny microbes such as bacteria, protozoa, fungi, and yeast help keep us alive.
Harmful microbes are the minority.
Soil bacteria convert nitrogen gas to a usable form for plants.
They help produce foods (bread, cheese, yogurt, beer, wine).
90% of all living mass.
Helps purify water, provide oxygen, breakdown waste.
Lives beneficially in your body (intestines, nose).

11. Populations, Communities, and Ecosystems
Members of a species interact in groups called populations.
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.

12. Populations
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.
Figure 3-4

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

14. The population of all species living & interacting in an area.
Community
The population of all species living & interacting in an area.
                                                

15. Ecosystems
Ecosystems consist of nonliving (abiotic) and living (biotic) components.
Figure 3-10

16. The Biosphere
The biosphere is the region within which all living things are found on Earth, extending from the bottom of the oceans to the upper atmosphere.
The biosphere is but one of the four separate components of the geochemical model along with the lithosphere, hydrosphere, and atmosphere.
The Gaia Hypothesis maintains that the Earth is a single self-regulating complex evolving system. An example being the exchange of elements between oceans and land.

17. THE EARTH’S LIFE SUPPORT SYSTEMS
The biosphere consists of several physical layers that contain:
Air
Water
Soil
Minerals
Life
Figure 3-6

18. Biosphere Atmosphere Stratosphere Hydrosphere Lithosphere
Membrane of air around the planet.
Stratosphere
Lower portion contains ozone to filter out most of the sun’s harmful UV radiation.
Hydrosphere
All the earth’s water: liquid, ice, water vapor
Lithosphere
The earth’s crust and upper mantle.

19. (living and dead organisms) (crust, top of upper mantle)
Oceanic
Crust
Continental
Crust
Atmosphere
Vegetation
and animals
Biosphere
Lithosphere
Soil
Upper mantle
Crust
Rock
Asthenosphere
Lower mantle
Core
Mantle
Figure 3.6
Natural capital: general structure of the earth.
Crust (soil and rock)
Biosphere
(living and dead organisms)
Hydrosphere (water)
Lithosphere
(crust, top of upper mantle)
Atmosphere (air)
Fig. 3-6, p. 54

20. Habitat
An organism’s habitat is the physical place or environment in which it lives.
Organisms show a preference for a particular habitat type, but some are more specific in their requirements than others.
Most frogs, like this leopard frog, live in or near fresh water, but a few can survive in arid habitats.
Lichens, fungi & algae or bacteria, are found on rocks, trees, and bare ground.

21. Habitat Needs
Cover – shelter; trees, shrubs, etc.
Water
Nutrients

22. Macronutrients
Chemicals organisms need in large numbers to live, grow, and reproduce.
Ex. carbon, oxygen, hydrogen, nitrogen, calcium, and iron.

23. Micronutrients
These are needed in small or even trace amounts.
Ex. sodium, zinc copper, chlorine, and iodine.

24. Presence of other organisms
Ecological Niche
The ecological niche describes the functional position of an organism in its environment.
A niche comprises:
the habitat in which the organism lives.
the organism’s activity pattern: the periods of time during which it is active.
the resources it obtains from the habitat.
Adaptations
Habitat
Activity
patterns
Presence of other organisms
Physical
conditions

25. The Fundamental Niche
The fundamental niche of an organism is described by the full range of environmental conditions (biological and physical) under which the organism can exist.
The realized niche of the organism is the niche that is actually occupied. It is narrower than the fundamental niche.
This contraction of the realized niche is a result of pressure from, and interactions with, other organisms.

26. Factors That Limit Population Growth
Availability of matter and energy resources can limit the number of organisms in a population.
Figure 3-11

27. Law of Tolerance
The law of tolerance states that “For each abiotic factor, an organism has a range of tolerances within which it can survive.”
Tolerance range
Optimum range
Number of organisms
Unavailable niche
Marginal niche
Preferred niche
Marginal niche
Unavailable niche
Examples of abiotic factors that influence size of the realized niche
Too acidic pH
Too alkaline
Too cold
Temperature
Too hot

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

29. Population Growth Cycle
Limited Resources
A population can grow until competition for limited resources increases & the carrying capacity (C.C.) is reached.

30. Typical Phases 1. The population overshoots the C.C.
2. This is because of a reproductive time lag (the period required for the birth rate to fall & the death rate to rise).
3. The population has a dieback or crashes.
4. The carrying capacity is reached.

31. 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

32. Producers: Basic Source of All Food
Most producers capture sunlight to produce carbohydrates by photosynthesis:

33. 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 (H2S) gas .

34. 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

35. Sun Chloroplast in leaf cell Chlorophyll H2O Light-dependent Reaction
Figure 3.A
Simplified overview of photosynthesis. In this process, 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, such as glucose, and oxygen.
H2O
Light-dependent
Reaction O2
Energy storage
and release
(ATP/ADP)
Glucose
Light-independent
reaction
CO2
Sunlight
6CO2 + 6 H2O
C6H12O6 + 6 O2
Fig. 3-A, p. 59

36. Consumers: Eating and Recycling to Survive
Consumers (heterotrophs) get their food by eating or breaking down all or parts of other organisms or their remains.
Herbivores
Primary consumers that eat producers
Carnivores
Primary consumers eat primary consumers
Third and higher level consumers: carnivores that eat carnivores.
Omnivores
Feed on both plant and animals.

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

38. Termite and carpenter ant work Bark beetle engraving
Scavengers
Decomposers
Termite and carpenter ant work
Bark beetle engraving
Carpenter ant galleries
Long-horned beetle holes
Dry rot fungus
Wood reduced to powder
Figure 3.13
Natural capital: various scavengers (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.
Mushroom
Time progression
Powder broken down by decomposers into plant nutrients in soil
Fig. 3-13, p. 61

39. Aerobic and Anaerobic Respiration: Getting Energy for Survival
Organisms break down carbohydrates and other organic compounds in their cells to obtain the energy they need.
This is usually done through aerobic respiration.
The opposite of photosynthesis

40. Aerobic and Anaerobic Respiration: Getting Energy for Survival
Anaerobic respiration or fermentation:
Some decomposers get energy by breaking down glucose (or other organic compounds) in the absence of oxygen.
The end products vary based on the chemical reaction:
Methane gas
Ethyl alcohol
Acetic acid
Hydrogen sulfide

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

42. Decomposition
As plant or animal matter dies it will break down and return the chemicals back to the soil.
This happens very quickly in tropical rainforest which results in low-nutrient soils.
Grasslands have the deepest and most nutrient rich of all soils

43. BIODIVERSITY
Figure 3-15

44. 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

45. Biodiversity Loss and Species Extinction: Remember HIPPCO
H for habitat destruction and degradation
I for invasive species
P for pollution
P for human population growth
C for Climate Change
O for overexploitation

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

47. Solutions Goals, strategies and tactics for protecting biodiversity.
Figure 3-16

48. ENERGY FLOW IN ECOSYSTEMS
Food chains and webs show how eaters, the eaten, and the decomposed are connected to one another in an ecosystem.
Figure 3-17

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

50. Energy Flow in an Ecosystem: Losing Energy in Food Chains and Webs
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.

51. 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

52. 10% Rule
We assume that 90% of the energy at each energy level is lost because the organism uses the energy. (heat)
It is more efficient to eat lower on the energy pyramid. You get more out of it!
This is why top predators are few in number & vulnerable to extinction.

53. 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.
Figure 3-20

54. 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).
Figure 3-21

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

56. What Sustains Life on Earth?
Solar energy, the cycling of matter, and gravity sustain the earth’s life.
Figure 3-7

57. MATTER CYCLING IN ECOSYSTEMS
Nutrient Cycles: Global Recycling
Global 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.

58. The Water Cycle
Figure 3-26

59. Water’ Unique Properties
There are strong forces of attraction between molecules of water.
Water exists as a liquid over a wide temperature range.
Liquid water changes temperature slowly.
It takes a large amount of energy for water to evaporate.
Liquid water can dissolve a variety of compounds.
Water expands when it freezes.

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

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

62. The Carbon Cycle

64. Effects of Human Activities on Carbon Cycle
We alter the carbon cycle by adding excess CO2 to the atmosphere through:
Burning fossil fuels.
Clearing vegetation faster than it is replaced.
Figure 3-28

65. Carbon Cycling
Carbon cycles as gaseous carbon is fixed in the process of photosynthesis and returned to the atmosphere in respiration.
Carbon may remain locked up in sinks or reservoirs that are biotic or abiotic for long periods of time, e.g. in the wood of trees, oceans or in fossil fuels such as coal or oil.
Indirectly carbon forms carbonate deposits as carbon is removed from the atmosphere. (The carbonate is stored mostly in the marine ecosystem.)
Humans have disturbed the balance of the carbon cycle through activities such as combustion and deforestation.
Burning fossil fuels
Petroleum & Coal

66. The Nitrogen Cycle: Bacteria in Action

67. Nitrogen Cycle Most of the work done by bacteria & decomposers Process
Product
Formulas
Nitrogen Fixation
Ammonia
N2 → NH4
Nitrification
Nitrite then nitrate
NH4 → NO2 →NO3
Assimilation
Proteins: amino acids, DNA
NO3 (some NH4) → uptake by plant
Ammonification (Decay & waste products)
Plant & animal decay & excretions → NH4
Denitrification
Nitrogen gas
NO3 → N2

69. Nitrogen in the Environment
Nitrogen cycles between the biotic and abiotic environments. The largest reservoir for nitrogen is the atmosphere and thus it is difficult to fix, bacteria play an important role in this transfer.
Nitrogen-fixing bacteria are able to fix atmospheric nitrogen.
Nitrifying bacteria convert ammonia to nitrite, and nitrite to nitrate.
Denitrifying bacteria return fixed nitrogen to the atmosphere.
Atmospheric fixation also occurs as a result of lightning discharges.
Humans intervene in the nitrogen cycle by producing and applying nitrogen (nitrates) fertilizers which is the main cause of eutrophication.
Lightning can fix atmospheric nitrogen
Bacteria on the roots of legumes can fix nitrogen

70. Effects of Human Activities on the Nitrogen Cycle
We alter the nitrogen cycle by:
Adding gases that contribute to acid rain.
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.
Releasing nitrogen into the troposphere through deforestation.

71. 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

72. The Phosphorous Cycle mining Fertilizer excretion Guano agriculture
weathering
uptake by
autotrophs
uptake by
autotrophs
leaching, runoff
Marine
Food
Webs
Dissolved
in Ocean
Water
Dissolved
in Soil Water,
Lakes, Rivers
Land
Food
Webs
death,
decomposition
death,
decomposition
Figure 3.31
Natural capital: simplified model of the phosphorus cycle. Phosphorus reservoirs are shown as boxes; processes that change one form of phosphorus to another are shown in unboxed print. QUESTION: What are three ways in which your lifestyle directly or indirectly affects the phosphorus cycle? (From Cecie Starr and Ralph Taggart, Biology: The Unity and Diversity of Life, 9th ed., Belmont, Calif.: Wadsworth © 2001)
weathering
sedimentation
settling out
uplifting over
geologic time
Marine Sediments
Rocks
Fig. 3-31, p. 77

73. Phosphorus Cycling
Phosphorus cycling is very slow and tends to be local and stable; in aquatic and terrestrial ecosystems, phosphorous is a sedimentary cycle.
Phosphorous is lost from ecosystems through run-off, precipitation, and sedimentation.
A very small amount of phosphorus returns to the land as guano (manure of fish-eating birds). Weathering and phosphatizing bacteria return phosphorus to the soil.
Often the Limiting factor in the ecosystem
The phosphorous cycle has no real significant gas phase and under many conditions will form stable insoluble compounds
Deposition as guano…
Loss via sedimentation…
Fertilizer production

74. 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 contributing to eutrophication

75. The Sulfur Cycle
Figure 3-32

76. Acidic fog and precipitation
Water
Sulfur
trioxide
Sulfuric acid
Acidic fog and precipitation
Ammonia
Ammonium
sulfate
Oxygen
Sulfur dioxide
Hydrogen sulfide
Plants
Dimethyl sulfide
Volcano
Industries
Animals
Ocean
Figure 3.32
Natural capital: simplified model of the sulfur cycle. The movement of sulfur compounds in living organisms is shown in green, blue in aquatic systems, and orange in the atmosphere. QUESTION: What are three ways in which your lifestyle directly or indirectly affects the sulfur cycle?
Sulfate salts
Metallic
sulfide
deposits
Decaying matter
Sulfur
Hydrogen sulfide
Fig. 3-32, p. 78

77. Molecular bridges in proteins
Sulfur Cycling
Sulfur is naturally occurring in rock or mineral forms and is a sedimentary cycle.
Sulfur is an essential component of proteins and is important in determining the acidity of precipitation, surface water, and soil.
Sulfur circulates through the biosphere as:
hydrogen sulfide (H2S), sulfur dioxide (SO2), sulfate (SO42-), and elemental sulfur (S)
Sulfur in petrol
Molecular bridges in proteins
Elemental sulfur

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

79. HOW DO ECOLOGISTS LEARN ABOUT ECOSYSTEMS?
Ecologist go into ecosystems to observe, but also use remote sensors on aircraft and satellites to collect data and analyze geographic data in large databases.
Geographic Information Systems
Remote Sensing
Ecologists also use controlled indoor and outdoor chambers to study ecosystems

80. 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

81. USDA Forest Service Private owner 1 Habitat type
Critical nesting site locations
USDA Forest Service
USDA
Forest Service
Private
owner 1
Private owner 2
Topography
Habitat type
Forest
Wetland
Figure 3.33
Geographic information systems (GISs) provide the computer technology for organizing, storing, and analyzing complex data collected over broad geographic areas. They enable scientists to overlay many layers of data (such as soils, topography, distribution of endangered populations, and land protection status).
Lake
Grassland
Real world
Fig. 3-33, p. 79

82. Systems Analysis
Ecologists develop mathematical and other models to simulate the behavior of ecosystems.
Figure 3-34

83. Identify and inventory variables Obtain baseline data on variables
Define objectives
Systems
Measurement
Identify and inventory variables
Obtain baseline data on variables
Make statistical analysis of
relationships among variables
Data
Analysis
Determine significant interactions
System
Modeling
Objectives Construct mathematical model
describing interactions among
variables
Figure 3.34
Major stages of systems analysis. (Modified data from Charles Southwick)
Run the model on a computer,
with values entered for different
Variables
System
Simulation
System
Optimization
Evaluate best ways to achieve
objectives
Fig. 3-34, p. 80

84. Importance of Baseline Ecological Data
We need baseline data on the world’s ecosystems so we can see how they are changing and develop effective strategies for preventing or slowing their degradation.
Scientists have less than half of the basic ecological data needed to evaluate the status of ecosystems in the United Sates (Heinz Foundation 2002; Millennium Assessment 2005).