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

2. 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

3. 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.

4. 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.

5. Genetic Diversity
In most natural populations individuals vary slightly in their genetic makeup.

6. ECOSYSTEM COMPONENTS
Life exists on land systems called biomes and in freshwater and ocean aquatic life zones.

7. Average annual precipitation
100–125 cm (40–50 in.)
75–100 cm (30–40 in.)
50–75 cm (20–30 in.)
4,600 m (15,000 ft.)
25–50 cm (10–20 in.)
3,000 m (10,000 ft.)
below 25 cm (0–10 in.)
1,500 m (5,000 ft.)
Coastal
mountain
ranges
Sierra
Nevada
Mountains
Great
American
Desert
Rocky
Mountains
Great
Plains
Mississippi
River Valley
Appalachian
Mountains
Figure 3.9
Natural capital: major biomes found along the 39th parallel across the United States. The differences reflect changes in climate, mainly differences in average annual precipitation and temperature.
Coastal chaparral
and scrub
Coniferous forest
Desert
Coniferous forest
Prairie grassland
Deciduous forest

8. Nonliving and Living Components of Ecosystems
Ecosystems consist of nonliving (abiotic) and living (biotic) components.

9. Falling leaves and twigs Soluble mineral nutrients
Oxygen (O2)
Sun
Producer
Carbon dioxide (CO2)
Secondary consumer
(fox)
Primary
consumer
(rabbit)
Precipitation
Producers
Falling leaves and twigs
Figure 3.10
Natural capital: major components of an ecosystem in a field.
Soil decomposers
Water
Soluble mineral nutrients
Fig. 3-10, p. 57

10. Factors That Limit Population Growth
Availability of matter and energy resources can limit the number of organisms in a population.

11. Producers: Basic Source of All Food

12. 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 .

13. 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.

14. Decomposers and Detritivores
Decomposers: Recycle nutrients in ecosystems.
Detritivores: Insects or other scavengers that feed on wastes or dead bodies.

15. 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

16. 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

17. Two Secrets of Survival: Energy Flow and Matter Recycle
An ecosystem survives by a combination of energy flow and matter recycling.

18. 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

19. 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

20. Energy Flow in Ecosystems
Food chains and food webs show how eaters, the eaten, and the decomposed are connected to one another
Ecologists assign each organism in an ecosystem to a trophic level
There is a decrease in the amount of energy available to each succeeding organism in a food chain or food web

23. The percentage of usable energy transferred as biomass from one trophic level to the next is called ecological efficiency
Ecological efficiency ranges from 2% - 40%

24. The pyramid of energy flow illustrates energy loss for a simple food chain assuming a 90% energy loss at each transfer
Energy flow pyramids explain why Earth can support more people if they eat at lower trophic levels

25. “weight” of biological material
Number of individuals
“weight” of biological material
Energy content
Ecological Pyramids

26. Pyramid of Numbers
Illustrates the number of organisms at each trophic level
Usually, organisms at the base of the pyramid are more numerous
Fewer organisms occupy each successive level
Do not indicate the biomass of the organisms at each level or the amount of energy transferred between levels
Figure 3-12   Pyramid of numbers. This pyramid is for a hypothetical area of temperate grassland; in this example, 10,000 grass plants support 10 mice, which support one bird of prey. Based on the number of organisms found at each trophic level, a pyramid of numbers is not as useful as other ecological pyramids. It provides no information about biomass differences or energy relationships between one trophic level and the next. (Note that decomposers are not shown.)

27. Pyramid of Biomass
Illustrates the total biomass at each successive trophic level
Biomass: measure of the total amt of living material
Biomass indicates the amount of fixed energy at a given time
Illustrates a progressive reduction in biomass through trophic levels
Figure 3-13   Pyramid of biomass. This pyramid is for a hypothetical area of temperate grassland. Based on the biomass at each trophic level, pyramids of biomass generally have a pyramid shape with a large base and progressively smaller areas for each succeeding trophic level. (Note that decomposers are not shown.)

28. Pyramid of Energy
Illustrates how much energy is present at each trophic level and how much is transferred to the next level
Most energy dissipates between trophic levels
Explains why there are so few trophic levels
Energy levels get too low to support life
Figure 3-14   Pyramid of energy. This pyramid indicates how much energy is present at each trophic level in a salt marsh in Georgia and how much is transferred to the next trophic level. Note the substantial loss of usable energy from one trophic level to the next; this loss is because of the energy used metabolically and given off as heat. (Note that decomposers are not shown. The 36,380 kcal/m2/year for the producers is gross primary productivity, or GPP, discussed shortly.)

29. 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.

30. 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).

31. What are nature’s three most productive and three least productive systems?

32. 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.

33. The Water Cycle

34. 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.

35. The Carbon Cycle: Part of Nature’s Thermostat

36. Figure 3.27
Natural capital: simplified model of the global carbon cycle. Carbon moves through both marine ecosystems (left side) and terrestrial ecosystems (right side). Carbon reservoirs are shown as boxes; processes that change one form of carbon to another are shown in unboxed print. QUESTION: What are three ways in which your lifestyle directly or indirectly affects the carbon cycle? (From Cecie Starr, Biology: Concepts and Applications, 4th ed., Pacific Grove, Calif.: Brooks/Cole, © 2000)

38. 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.

39. The Nitrogen Cycle: Bacteria in Action

42. 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.

43. Effects of Human Activities on the Nitrogen Cycle
Human activities such as production of fertilizers now fix more nitrogen than all natural sources combined.

44. The Phosphorous Cycle

46. 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.

47. The Sulfur Cycle

48. 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.

49. 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

50. 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.

52. The End