1. Concerned with community structure and population interactions
Community Ecology
Concerned with community structure and population interactions

2. Interactions Five categories Competition Predation Mutualism
Commensalism
Parasitism

3. Competition

4. Competition Interspecific competition
The competition between two or more species for some limiting resource
food or nutrients, space, mates, nesting sites
Resolutions
Competitive exclusion principle (Gause’s principle)
Resource partitioning
Character displacement
Realized niche
Competitive interactions between organisms can have a great deal of influence on species evolution

5. The Competitive Exclusion Principle
G.F. Gause-worked with 2 strains of Paramecium
-States that two species competing for the same limiting resources cannot coexist in the same place
When two species compete, one is likely to be more successful.
Cannot coexist if they share the same niche.
One species could become extinct or evolve to exploit different resources resource partitioning)
Divergence in adaptation is called character displacement.
Animation

6. Ecological Niches The ecological niche
Is the total of an organism’s use of the biotic and abiotic resources in its environment
The niche concept allows restatement of the competitive exclusion principle
Two species cannot coexist in a community if their niches are identical
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7. Resource Partitioning
Resource partitioning is the differentiation of niches
A. insolitus usually perches on shady branches.
A. distichus perches on fence posts and other sunny surfaces.
A. distichus
A. ricordii
A. insolitus
A. christophei
A. cybotes
A. etheridgei
A. alinigar
That enables similar species to coexist in a community
Minimizes competition & maximizes success

8. Resource Partitioning
Resource partitioning is a way in which different species can use the same resource, such as food, without occupying the same physical location at the same point in time. In this example, the different warblers eat the same caterpillar, but they occupy different positions in the tree. Two primarily occupy the area near the trunk, with the others share the edges of the branches, but at different heights. The result is the warblers do not overtly compete for food in the same space.

9. Character Displacement (niche shift)
As a result of resource partitioning.
-Divergence in adaptation
G. fortis
Beak depth (mm)
G. fuliginosa
Beak depth
Los Hermanos
Daphne
Santa María, San Cristóbal
Sympatric populations
G. fuliginosa, allopatric
G. fortis, allopatric
Percentages of individuals in each size class 40 20 8 10 12 14 16
There is a tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations of the same two species
Speciation:
Allopatric-geographic barriers
Sympatric- no geo barrier

10. Niche theory distinguishes between fundamental & realized niches:
fundamental = all possible conditions under which population reproduces itself
realized niche = the actual niche exhibited in particular time & place

11. Predation True predator Parasite Parasitoid Herbivore
Snowshoe Hare and Canadian Lynx

12. Camouflage Cryptic coloration
-passive defense
Cryptic coloration
Fur of snowshoe hare is white in winter and brown in summer
The larvae of some moths are colored like bird droppings
Marking on animals to blend in to background.
Lizard

13. Aposematic coloration (warning coloration)
Coloration that warns predators
Predators learn to associate color with bad taste or harmful chemical
Mimicry
Two types
Mϋllerian
Batesian

14. Müllerian mimicry Two or more unpalatable species resemble each other
(a) Cuckoo bee
(b) Yellow jacket

15. Batesian mimicry
A palatable or harmless species mimics an unpalatable or harmful model
(a) Hawkmoth larva
(b) Green parrot snake

16. passive defense
Spins, thorns, poisons
Hiding, fleeing

18. Community Interactions
Symbiosis
Predatory-Prey
Competition

19. Symbiosis
Mutualism (+/+)
Commensalisms (+/o)
Parasitism (+/-)

20. (+/+)
Mutualism

21. Commensalism One species benefits and the other is not affected
It is difficult to determine true commensalism because it is difficult to ensure host is not harmed.             Ex: Barnacles that attach themselves to the backs of whales

22. Parasitism (+/-)
Relationship in which one species benefits; while harming the other
Tomato hornworm covered with cocoons of pupating wasps

24. Diversity of Species in Ecosystems:
Species Diversity: variety of different organisms in a community…two components
Species Richness
Number of different species in a community
Relative Abundance
Proportion each species represents of all individuals in the community

25. Higher diversity communities are more resistant to invasive species
Higher diversity communities are more resistant to invasive species. These are organisms that have become established outside of the native range.
Diverse communities are better at partitioning resources and disallow the establishment of invasive species.

26. DOMINANT SPECIES KEYSTONE SPECIES
Species that is the most abundant or collectively occupies the most biomass.
These species become “dominant” due to:
-being competitively superior
-avoid predation**
-avoid disease**
**this may be why invasive species can thrive, natural parasites and predators may not attack invasives.
KEYSTONE SPECIES
Species that is not particularly abundant but exert strong control on community structure because of a pivotal niche.
Ex/ in tidal pools, starfish are important in maintaining the diversity by being a keystone predator and not allowing any one organism to become a dominant species.

27. Review of Community Interactions

28. Ecological Succession

29. Ecological Succession

30. Ecological Succession
Primary succession
Occurs where no soil exists when succession begins
Starts with pioneer species (lichens & mosses)

31. Ecological Succession
Secondary succession
Begins in an area where soil remains after a disturbance
takes place where a community has been removed, e.g., in a plowed field or a clear­cut forest

32. (a) Soon after fire. As this photo taken soon after the fire shows, the burn left a patchy landscape. Note the unburned trees in the distance.
(b) One year after fire. This photo of the same general area taken the following year indicates how rapidly the community began to recover. A variety of herbaceous plants, different from those in the former forest, cover the ground.