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

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

3. Cells Are the Basic Units of Life
Cells: the smallest and most fundamental unit of life
Cell theory: all living things are made up of cells
Eukaryotic vs. prokaryotic

4. Cells Are the Basic Units of Life

5. Ecologists Study Connections in Nature
Ecology: The study of how organisms interact with their biotic and abiotic environment
Levels of organization

6. Ecologists Study Connections in Nature
Level of Organization
Example
Analogy
Atoms
Oxygen
Molecule
H2O
Cell
Muscle cell
Organism
Fox
Population
All of the foxes in Hopewell
Community
All of the forest creatures in Hopewell
Ecosystem
Deciduous forest
Biosphere
Earth
Ecologists Study Connections in Nature

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

8. The Earth’s Life-Support System Has Four Major Components
Biosphere
Atmosphere
Hydrosphere
Geosphere

9. Three Factors Sustain Life on Earth
The one way flow of high-quality energy
The cycling of matter or nutrients
Gravity

10. What Happens to Solar Energy Reaching the Earth?
We get electromagnetic waves: visible light, UV radiation, heat
Absorbed by the earth’s atmosphere, clouds and surface –OR-
Reflected back into space (most of the energy)
Maintains sufficient temperature for life  powers the water cycle
0.1% of total energy reaching the surface powers photosynthesis.

11. What Happens to Solar Energy Reaching the Earth?
Greenhouse Effect
Greenhouse gases: water vapor, CO2, methane, nitrous oxide, ozone
Hold on to heat and make life possible on Earth
Human activities are increasing the amount of some greenhouse gases
CO2: burning of fossil fuels, deforestation, etc.
Methane and nitrous oxide: more livestock.

13. What Are the Major Components of an Ecosystem?
Ecosystems contain living (biotic) and nonliving (abiotic) components.
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.

14. Ecosystems Have Living and Nonliving Components
Abiotic
Nonliving
Ex. Water, air, rocks, heat, nutrients, etc.
Biotic
Living or once living
Ex. Plants, animals, microbes, dead things, etc.

15. Ecosystems Have Living and Nonliving Components
Different organisms thrive under different conditions
Range of tolerance
May vary by age, health, or genetics in a given population
Outside of this range, it is difficult for a population to survive.

17. Several Abiotic Factors Can Limit Population Growth
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
Biggest limiting factor on land is usually water
Aquatic limiting factors include temperature, sunlight, and salinity.

18. Producers and Consumers Are the Living Components of Ecosystems
Aka autotrophs (literally “self feeding)
Make their own food from inorganic material through photosynthesis or chemosynthesis
Photosynthesis  plants
Chemosynthesis  some bacteria.

19. Producers and Consumers Are the Living Components of Ecosystems
Aka heterotrophs (literally “other feeding”)
Must consume other organisms or their remains for energy
Ex. Animals and fungus

21. Consumers Primary consumers Secondary consumers
Herbivores
Ex. Rabbits, grasshoppers, etc.
Secondary consumers
Carnivores
Ex. Spiders, birds, etc.
Third level and up consumers
Ex. Wolves, tigers, etc.

22. Consumers Omnivores Decomposers Detritivores
Feed on both plants and animals
Ex. Humans, pigs, cockroaches, etc.
Decomposers
Feed on dead organisms
Ex. Fungi and bacteria
Detritivores
Feed on the wastes or dead bodies of organisms
Ex. Mites, earthworms, vultures, etc.

23. Energy All organisms get their energy through respiration
Aerobic respiration
Uses oxygen to release energy from glucose
In general, opposite process of photosynthesis
Anaerobic respiration
Occurs in the absence of oxygen
Results in fermentation (ex. Alcohol and lactic acid).

24. Energy Flow and Nutrient Cycling
Remember: One-way energy flow and nutrient cycling (2 scientific principles of sustainability)
Decomposers and detritivores (often microscopic organisms) are crucial to this process because they break down organic matter to be used again

25. What Happens to Energy in an Ecosystem?
Energy flows through ecosystems in food chains and webs.
As energy flows through ecosystems in food chains and webs, the amount of chemical energy available to organisms at each succeeding feeding level decreases.

26. Energy Flows through Ecosystems in Food Chains and Food Webs
Chemical energy stored as nutrients flows through ecosystems from one trophic level to the next
Plant  Caterpillar  Robin  Hawk
Decomposers and detritivores consume all of them when they die
Every time we go from one level of the chain to the next, most energy is lost to heat and metabolic activities.

27. Food Chains and Food Webs
Most consumers feed on more than one type of organism, and most organisms are eaten by more than one type of consumer
Food webs are illustrations of the complex network of possible food chains in a given ecosystem.

28. Food Chain

29. Food Web

30. Usable Energy Decreases with Each Link in a Food Chain or Web
Biomass: dry weight of all organic matter contained in a single or group of organisms
When an organism is consumed by another, the chemical energy stored in its biomass is transferred to the consumer
With each transfer, some usable chemical energy is lost as heat.

31. Ecological Efficiency
Percentage of usable chemical energy transferred from one trophic level to the next
Ranges from 2-40% depending on the organisms, but 10% is about average
Because of this, the image of a pyramid is helpful to illustrate energy flow.

32. Energy Pyramid
Populations in an Ecosystem
Biomass in an Ecosystem

33. Interesting factoid
Energy pyramids show how the earth can support more people if they eat at lower trophic levels (i.e. less meat, more veggies and other plants)

34. GPP, NPP and ABC Gross primary productivity (GPP):
the rate at which an ecosystem’s producers (usually plants) convert solar energy into chemical energy
Measured in energy production per unit area per time span (ex. kcal/m2/year)
Net primary productivity (NPP):
the rate at which energy is produced minus the rate at which the energy is used (respiration)
NPP = GPP – R.

35. NPP

36. What Happens to Matter in an Ecosystem?
Matter, in the form of nutrients, cycles within and among ecosystems in the biosphere, and human activities are altering these chemical cycles.

37. Water Cycle
Aka hydrologic cycle
Transpiration

38. Water Cycle and Humans
Withdrawal of freshwater from streams, lakes and underground
Clear vegetation for agriculture and development
Increased flooding.

39. Carbon Cycle
Movement depends on the cycle of photosynthesis and cellular respiration
Humans and the carbon cycle  increasing levels of CO2
Clearing of trees and other plants
Burning of fossil fuels and wood.

40. Nitrogen Cycle
Most nitrogen is found in our atmosphere as a gas (78% of our atmosphere)
Important for organisms because it is a building block of proteins
Atmospheric nitrogen is made usable by nitrogen-fixing bacteria
Then absorbed by plants, which are then eaten by consumers
Returned back to the atmosphere/cycle through waste and decay of dead organisms.

41. Nitrogen Cycle and Humans
Burning of fossil fuels (nitric oxide)  acid rain
Livestock wastes and inorganic fertilizers increase nitrous oxide (greenhouse gas)
Destruction of forests, grasslands, and wetlands
Agricultural runoff and sewage
Nitrogen rich crops.

42. Phosphorous Cycle
Does not include the atmosphere as it cycles through an ecosystem
Very slow in comparison to other cycles
Important for ATP
Usable form is in rocks and soil
Human impact  increased flooding, runoff and erosion cause phosphates to be “lost” for long periods of time in the ocean.

43. Sulfur Cycle Slow moving nutrient
Found mostly in rocks and deep-ocean sediment
Human impact
Burning fossil fuels
Fossil fuel refining process
Metal refining process.