1. Chapter 53 ~ Community Ecology

2. Community structure Community Species diversity
Richness & Abundance…….
Species diversity
Hypotheses: Contrasting views
•Individualistic ~independently distributed along gradient, similar abiotic needs b/w species
•Interactive: species closely interdependent and nearly always occur together.

3. Interactions
Interspecific (interactions between populations of different species within a community):
Competition
Predation
Mutualism
Commensalism

4. Competition for Resources
Interspecific Competition:
Grasshoppers vs. Bison for grass
Lynx vs. fox for hares
Competition for same resource
Competitive Exclusion Priniciple
Reproductive advantage of one over another causes????
Eventually elimination of weaker/inferior
Ecological Niche:
“ecological role”: no two species can have same niche
Resource Partitioning
Extinction or evolution to different resource of weaker
Character Displacement
Allopatric and Sympatric speciation

5. Predation Lion Killing prey Bison eating plants (herbivory)
Parasite on host organism (parasitism)
Predator Adaptation
Acute senses
Claws, teeth, fangs, poisons
Plant Defenses
Animal Defenses against predators

6. Animal Predation defense
Cryptic coloration (camouflage)
Aposematic coloration (warning) may have effective chemical defense also.
Mimicry~ superficial resemblance to another species
Batesian~ palatable/ harmless species mimics an unpalatable/ harmful model
Mullerian~ 2 or more unpalatable, aposematically colored species resemble each other

7. IndoMalayan Octopus Mimicry Octopus

8. Mutualism
Commensalism

9. Trophic Structures
Feeding relationships b/w organisms of the community
Food Chain: Transfer of energy from its source in plants through herbivores, carnivores finally to decomposers.
Trophic Levels: length of food chain limit to 4-5 levels/links.
Food Web: Not linear chain, but interactive.

10. Limit of Food Chain Food chain only 4-5 levels or smaller WHY?
Energetic Hypothesis:
Inefficiency of energy transfer (10%)
100kg10kg1kg
Dynamic Stability hypothesis
Long food chains less stable than short
Fluctuations at bottom magnified at top (predator adaptation)

11. Dominant Species Highest abundance in a community
Highest Biomass (sum weight of all individuals in a pop)
Sugar Maple dominant in eastern N. America
What happens when dominant species is lost??
American Chestnut Dominant in deciduous forest (canopy tree)
Chestnut Blight fungus brought over from China (1910)
Killed all chestnuts
Over all very little impact
………except
56 species of insect fed on Chestnut tree
7 became extinct (sole food source)

12. Keystone Species Not abundant in community
Sea Otter abundance depends on
Sea urchin biomass
Kelp density
Food chain illustrates hypothetical changes due to killer whale predation
Not abundant in community
Exert a strong control on community structure
Best ways to recognize Keystone is to remove it in a controlled area

13. Disturbance of the Community
Stability: state of equilibrium
Non-equilibrium Model:
Constant change
Role of disturbances
Natural Occurrence
Human Interference

14. Succession
Ecological succession~ transition in species composition over ecological time
Primary~ begun in lifeless area; no soil, perhaps volcanic activity or retreating glacier
Secondary~ an existing community has been cleared by some disturbance that leaves the soil intact