1. Ecology -Communities (Part 2)-

2. Communities - Processes between Populations
+ = beneficial to a species
= detrimental to a species
0 = species is unaffected
Kinds of Interactions
Interaction
Species 1
Species 2
Competition -
Predation +
Herbivory
Parasitism
Disease
Mutualism
Commensalism

3. Communities - Processes between Populations
Competition
A (+, -) interaction between members of the same species (Intraspecific) or between members of different species (Interspecific) for resources that are in short supply
Resources can be food, water, mates, nesting sites etc.

4. Communities - Processes between Populations
Competition
Gause - Experiments with Paramecium
Paramecium aurelia Paramecium caudatum

5. Communities - Processes between Populations
Competition
Gause - Experiments with Paramecium
P. aurelia alone
P. caudatum alone
previous P. aurelia
P. aurelia
P. caudatum
Grown together

6. Communities - Processes between Populations
Competition
From Gause’s Paramecium experiments
Competitive exclusion principle
When two species compete for the same limited resource, one species will eventually eliminate the other.

7. Communities - Processes between Populations
Competition
Ecological niche
The total of species’ use of biotic and abiotic resources in its environment
Eugene Odum
- the habitat is a species address, the niche is its “profession”.

8. = dN (K - N) dt rN K Remember equation for logistic population growth
Two new terms:
α = effect* of species 2 on species 1
β = effect* of species 1 on species 2
*‘effect’ means how much the growth of a population is decreased

9. = = dN1 (K1 – N1- α N2) dt r1N1 K1 dN2 (K2 – N2- β N1) dt r2N2 K2
Logistic population growth and competition
dN1 dt
(K1 – N1- α N2) K1 =
r1N1
Effect of species 2 on species 1 depends on the degree of the effect (α) and the numbers of species 2
dN2 dt
(K2 – N2- β N1) K2 =
r2N2
Effect of species 1 on species 2 depends on the degree of the effect (β) and the numbers of species 1

10. Logistic population growth and competition
P. aurelia if alone α
P. aurelia in competition
P. caudatum if alone β
P. caudatum in competition
P. aurelia is species 1
Effect of aurelia on caudatum is β
P. caudatum is species 2
Effect of caudatum on aurelia is α

11. Communities - Processes between Populations
Competition
How do species respond to competition?
Character displacement
Geographical distribution of species B
Geographical distribution of species A
Area of
Sympatry (and competition)

12. Communities - Processes between Populations
Competition
How do species respond to competition?
Character displacement
Geospiza
fuliginosa
Geospiza fortis

13. Communities - Processes between Populations
Competition
How do species respond to competition?
Character displacement
Beak depth (and therefore the kind of food eaten) changes in sympatric area

14. Communities - Processes between Populations
Competition
How do species respond to competition?
2. Resource Partitioning
-differentiation of ecological niches that allows two species to coexist

15. Communities - Processes between Populations
Myrtle warbler
Bay breasted warbler
Cape May warbler
All eat the same food
(insects) and live in the same trees

16. Communities - Processes between Populations
Competition
2. Resource Partitioning
Cape May warbler
Bay breasted warbler
Myrtle warbler

17. Communities - Processes between Populations
Competition
2. Resource Partitioning

18. Communities - Processes between Populations
Mutualism
Any interaction between members of two species that is beneficial to both

19. Communities - Processes between Populations
Mutualism - Corals and Algae
Mesoglea
Gastrodermis
Ectodermis • • • • •
zooxanthellae •

20. Communities - Processes between Populations
Mutualism - Corals and Algae
Sugars to polyp
Nitrogen to zooxanthella

21. Communities - Processes between Populations
Predation
A (+, -) interaction between members of two species in which one species kills and eats members of the other

22. Communities - Processes between Populations
Predation
Predator and prey have co-evolved in response to one another
Predator evolves some
mechanism to be
a better predator
Prey evolves some
reponse to avoid the predator
Prey evolves some
reponse to avoid the predator

23. Communities - Processes between Populations
Predation
Some mechanisms for making predators more efficient
Incisor teeth (molars)
for piercing and holding prey
Carnassial teeth (molars)
for shearing meat

24. Communities - Processes between Populations
Predation
Some mechanisms for making predators more efficient
Spine acts as a spring to give extra thrust when running

25. Communities - Processes between Populations
Predation
How to avoid being prey
Mimicry
Either look like something distasteful
Have a number of distateful animals resemble one another or
Viceroy Monarch
Batesian Mimicry
Mullerian Mimicry

26. Communities - Processes between Populations
Predation
How to avoid being prey
Mimicry of other objects

27. Communities - Processes between Populations
Predation
How to avoid being prey
Evoke startle response

28. Communities - Processes between Populations
Predation
Populations of predators and
prey cycle slightly out of phase
with one another.

29. Communities - Processes between Populations
Predation

30. Communities - Processes between Populations
Predation
Holling’s Disk Equation

31. Top down vs bottom up controls
Two views on how community structure is controlled
Top-down mechanism
Bottom-up mechanism

32. Numbers of a prey species
Top-down control
Predator species
controls
Numbers of a prey species
controls
Numbers of a plant species

33. - Already seen an example of this
Top-down control
- Already seen an example of this
- after hunting of sea otters

34. Numbers of a plant species controls
Bottom-up control
Numbers of a plant species
controls
Nutrients
Numbers of a prey species
controls
Predator species

35. Bottom-up control Quantity and quality of grass Number of grasshoppers
Nitrogen, phosphorus