1. Communities

2. Communities are groups of populations within an area
When studying communities one of the first questions asked is “How diverse is it?”

3. Measurements of Diversity
Species Richness – Simple count of # of species
Relative abundance – Measure of how common or rare a particular species is in a community

4. Measurements of Diversity
Species evenness – How equal the relative abundances are
Species diversity – Takes into account both richness and evenness

5. Species Percent of community Deer 33% Wolf Mouse 34% Species
Zebra
85%
Lion 5%
Hyena
Elephant 3%
Leopard 1%
Species
Percent of community
Deer
33%
Wolf
Mouse
34%

6. Interspecific interactions
Effects on Populations
Competition
-/-
Predation
+/-
Parasitism
Mutualism
+/+
Commensalism
+/0

7. Populations are often in conflict over various resources
Competition
Populations are often in conflict over various resources
When two populations need the same resource competition may occur.
Competition results in the decrease in population density of one or both populations, or the local extinction of one population

8. Competitive Exclusion principle
When two populations occupy the same ecological niche they are unable to coexist.
Eventually the stronger competitor will drive the weaker competitor to local extinction.

10. Character displacement
Character traits tend to be more divergent in sympatric, competing, species than in allopatric species that are not competing
May eventually lead to resource partitioning

11. Includes carnivory, herbivory, seed eating.
Predation
Includes carnivory, herbivory, seed eating.
May also be extended to include parasitism and parasitoidism

12. The Evolutionary Arms Race
Predator and prey are often locked in a struggle to out-adapt one another
New adaptations in a predator will apply a selective pressure on prey populations
New adaptations in prey populations will apply a selective pressure on predator populations
Example of coevolution

15. Crypsis

18. Aposematism

20. Batesian – Harmless mimics harmful
Mimicry
Batesian – Harmless mimics harmful

21. Mullerian – harmful mimics harmful

22. Parasites and Parasitoids

24. Mutualism

26. Commensalism

27. Dominant Species The highest biomass in a community
Usually dominant by either being the best competitor or avoiding predators the best

28. Keystone Species May not be especially abundant
Have the strongest control over the community
When a keystone species is removed a large cascade effect dramatically changes the community

30. Bottom-Up and Top-Down
Communities may either be controlled by produces (bottom-up) or predators (top- down)

31. Disturbance
Disturbances such as fire can dramatically change the make- up of a community
The intermediate disturbance hypothesis suggests that communities that are constantly disturbed have low diversity, but so do communities that are never disturbed.

32. Ecological Succession
Primary – Lifeless area -> Autotrophs such as lichens and mosses. Soil develops.
Secondary – Existing community changes after a disturbance