1. Ecosystem and Community Dynamics
Unit 4: The Biosphere

2. Levels of Organization
Organism
Population (of one species)
Biological community (interacting, living populations)
Ecosystem (living and non-living)
Biome (many ecosystems – similar climate)
Biosphere (all biomes on earth)

3. Ecosystem Interactions
Chances for survival are increased when any one species uses the available resources in different ways.
Habitat – area where an organism lives
Niche – role or position that an organism has in its environment
Competition (resources) v. predation (plants too!)

4. Symbiotic Relationships
All examples of symbiosis – two (or more) species living closely together
Mutualism – two or more organisms that benefit from each other.
Commensalism –
one organisms benefits,
the other neither
benefits nor is harmed
(Nemo!).
Parasitism – one
organism benefits, the
other is harmed.
Mutualism – coral. Coral protects, algae provides nutrients!

5. Flow of Energy in an Ecosystem
Autotroph – collects energy from the sun to produce food
Heterotroph – gets its energy by consuming other organisms
Herbivore
Carnivore
Omnivores
Scavengers
Detritivores or decomposers – eat and break down parts of dead organisms and retain their nutrients so they can be reused
What would happen if decomposers didn’t exist?

6. Wood louse decomposing dead plants!

7. Models of Energy Flow Food chains and food webs
Have different trophic levels
Each step in the food chain/web
Arrows represent the flow of energy
Why would we use webs instead of chains?

9. Energy and Biomass Pyramids

10. How do the two relate?

11. Communities
(From earlier) A group of interacting populations that occupy the same area at the same time.
Living things only
Organisms adapt to the conditions under which they live.
What factors might influence tropical fish community?

12. Limiting Factors and Tolerance
Limiting factor – restricts the…of organisms
Numbers
Reproduction
Distribution
Could be biotic (ex. competition for food) or abiotic (temperature)
Range of tolerance – upper and lower limit of a particular limiting factor
Example: 9-25 oC for steelhead trout
Conditions under which they can live (might not necessary thrive)

13. Ecological Succession
How might an ecosystem respond to a drastic change in biotic/abiotic factors?
Example: forest fire

14. Primary Succession
The establishment of a community in an area of exposed rock that does not have any topsoil
Example: Solidified lava flow
First step: Lichens (a mutualistic relationship between a fungus and an algae) and mosses
As they die, make first layer of soil
Pioneer species
Later: Weedy plants (grasses and ferns)
Much later: Shrubs and trees

16. Secondary Succession
A process that occurs after a disturbance has taken place, but the soil remains
Example: forest fires
What’s different about the time scale?
Thought question: notice the species at the start and at the finish

17. When does succession “end?”
Unclear. (hard to tell)
Climax community – when a stable community has formed
What role
might humans
play?