1. Community Ecology
Chapter 41

2. What you need to know
The role of competitive exclusion in interspecific competition
The symbiotic relationships
How energy flows through the ecosystem via food chains and food webs
The role of habitat and niche as part of an organism’s life
The difference between primary and secondary succession

3. Community Relationships
Producer/consumer
Predator/prey relationship
Symbiosis
Parasitism:
One +
One –
Commensalism
One negligible
Mutualism
Both +

4. Habitats and Niches
Habitats are the part of the environment an organism lives (home address)
Niche is the role the organism plays in the habitat (job/profession; how it fits in)
Ecological niche: sum total of biotic and abiotic factors used by species
Fundamental niche: niche a species will normally occupy
Realized niche: niche the species actually occupies as a result of competition

5. Competitive Exclusion Principle
G.F. Gause
Grew protists separately with success
Put them together and one drove the other to extinction
Two species cannot coexist in a community if their niches are identical
One species will use the resources more efficiently

6. Resource Partitioning
Competitive exclusion does not always lead to the extinction of a species
Sometimes a species will modify its fundamental niche into a realized niche to survive

7. Important Species Dominant species: most abundant species
Keystone species: exert strong control on food web
Robert Paine – University of Washington

8. Wolves change Rivers https://www.youtube.com/watch?v=ysa5OBhXz-Q
Which one is it?

9. Diversity
Species diversity is often used to measure the health of an ecosystem
Increased diversity = increased survivability

10. Ecological Succession
Colonization of barren environments
Sequence of specific steps
Primary Succession
Colonization of new, previously uninhabited placed (new islands, lava deposits)
Secondary succession
Recolonization of previously inhabited, but destroyed environments (wildfires, floods, vast storms)

11. Primary Succession
Erosion of rock by water/weather leading to thin layer of soil (nutrient poor)
Pioneer species arrive
Lichens, mosses, and fungus: cause further erosion, organic matter (detritus)
Hardy, low growing plants and grasses
Larger plants, larger animals

12. Primary Succession Shrubs, pine trees, and predators
Climax community: biome that is expected according to climate.
Pioneer species are replaced
Timeline = hundreds of years

13. Secondary Succession Presence of soil and surviving roots
Fire-activated seeds germinate, root balls sprout
Fast growth and recovery
Climax community similar to old one
Invasive species
Timeline: 1-2 years

14. Secondary Succession

15. Food Chain
Linear feeding relationship between several organisms

16. Food Web
Interconnected feeding relationships in an ecosystem among many organisms (multiple food chains)

17. The Pyramids
Divided into trophic levels which represent individual organisms/populations
Energy Pyramid
Biomass Pyramid
Pyramid of Numbers

18. Energy Pyramid Producers trophic level (bottom): most energy stored
Primary consumers: less energy
Secondary consumers: less energy
Energy is lost in the daily function of organisms

19. Biomass Pyramid Biomass: amount of living matter at each trophic level
Usually expressed as grams/unit area
Highest biomass is always at the bottom (producers)

20. Pyramid of Numbers Number of individuals at each trophic level Meadow
1,000 grasses
200 caterpillars
10 birds
1 hawk
Forest
10 trees