1. The Living World – Part 2
AP Env Sci

2. All Ecosystems Have a Similar Biotic Structure
In Summary
All Ecosystems Have a Similar Biotic Structure

3. Food Chains and Food Webs

4. Food Chain or Food Web ? Food Chain:
Squirrel eats the nut, fox eats the squirrel.
Caterpillar eats the leaf, warbler eats the caterpillar, hawk eats the warbler.
Food Chain is a specific pathway.
Food Web:
Collection of all food chains
Interconnected pathways

5. A Food Web

6. How Many Trophic Levels?
Usually no more than three or four in terrestrial ecosystems.
Sometimes five in marine ecosystems.
Why?
Heterotrophs are not as “efficient” as autotrophs
At each higher trophic level, biomass is 90% less than level before
Biomass: total combined mass of all organisms at given trophic level

7. The Biomass Pyramid

8. Why a Pyramid Instead of a Rectangle?
Much food consumed by heterotrophs is not converted to body mass.
Much of the biomass of the producer goes directly to decomposers.
Consumers that eat consumers must be larger than what they are eating. Sets Limits.

9. Energy Flow Pyramid
Similar to Biomass Pyramid (matter is NOT energy)
Average 90% Loss at each level
Ecological Efficiency

10. Non-Feeding Relationships
Mutually Supportive:
Mutualism: benefit to both species
Example: flower/pollinating insects
Symbiotic:
Symbiotic relationships can be mutualistic or parasitic
Flea: not mutualistic

12. Non-Feeding Relationships: Competitive
All-Out competition is rare – each species occupies own habitat or ecological niche
Ecological Niche:
What animal feeds on
Where it feeds
When it feeds
Where it finds shelter
Response to abiotic factors
Nesting

13. Non-Feeding Relationships: Competitive
Resource Partitioning
Both Competitors Can Thrive
Apparent Competitors Occupy Different Niches:
Bats vs. Swallows
Both eat flying insects
Bats: night-flying insects
Swallows: day-flying insects
Competitive Exclusion Principle
Direct Competition Eliminates One Competitor
Example: European rabbit in Australia -> demise of several marsupial species