1. Ecology -Communities-

2. Communities & Populations
Ways to characterize communities
Diversity
Keystone species
Disturbance and Succession
• Processes at work in communities
Competition
Predation
Commensalism/mutualism

3. Community
- an assemblage of populations of various species living close enough to potentially interact.

4. Communities - Diversity
Measuring Diversity
-diversity is a measure that evaluates the number
of species and the number of organisms in each species in an area

5. Communities - Diversity
Shannon Diversity index
natural logarithm
H’ = -Σ pi ln pi
Shannon diversity index
proportion of ith species
Sum of

6. Communities - Diversity
Examples - intertidal zone in New Brunswick
Sample and count
the number of each species

7. Communities - Diversity
Examples - intertidal zone in New Brunswick
SPECIES
Species 1
Species 2
Species 3
Species 4
Species 5
Species 6
Species 7
Species 8
Species 9
Species 10

8. Communities - Diversity
Examples - intertidal zone in New Brunswick
SPECIES
NUMBER
Species 1 71
Species 2 18
Species 3 1
Species 4 59
Species 5 5
Species 6 11
Species 7 15
Species 8
Species 9
Species 10 4
Total = 200

9. Communities - Diversity
Examples - intertidal zone in New Brunswick
SPECIES
NUMBER pi
Species 1 71
71/200 = 0.355
Species 2 18
18/200 = 0.09
Species 3 1
0.005
Species 4 59
.295
Species 5 5
0.025
Species 6 11
0.055
Species 7 15
0.075
Species 8
Species 9
Species 10 4
0.02
Total = 200

10. Communities - Diversity
Examples - intertidal zone in New Brunswick
SPECIES
NUMBER pi
lnpi
Species 1 71
71/200 = 0.355
.126
Species 2 18
18/200 = 0.09
.008
Species 3 1
0.005
Species 4 59
.295
.087
Species 5 5
0.025
.0006
Species 6 11
0.055
.003
Species 7 15
0.075
.00562
Species 8
Species 9
Species 10 4
0.02
.0004
Total = 200

11. Communities - Diversity
Examples - intertidal zone in New Brunswick
SPECIES
NUMBER pi
lnpi
pilnpi
Species 1 71
71/200 = 0.355
-1.036
-0.368
Species 2 18
18/200 = 0.09
-2.408
-0.217
Species 3 1
0.005
-5.298
-0.026
Species 4 59
.295
-1.221
-0.36
Species 5 5
0.025
-3.689
-0.092
Species 6 11
0.055
-2.9
-0.16
Species 7 15
0.075
-2.59
-0.194
Species 8
Species 9
Species 10 4
0.02
-3.912
-0.078
Total = 200
H’ = 1.716
H’ = -Σ pi ln pi

12. H’ = 1.774 If we remove the two most common species, (was 1.716)
NUMBER
Species 1 71
Species 2 18
Species 3 1
Species 4 59
Species 5 5
Species 6 11
Species 7 15
Species 8
Species 9
Species 10 4
Total = 200
(was 1.716)

13. Imagine a community that has (potentially) 5 species of tree
Look at 3 different forests

14. Forest 1
Forest 2
Forest 3

15. Forest 1
Forest 2
Forest 3 1 2 3 10 36 4 48
Total 50 H E

16. 1 pi
lnpi
pilnpi 10
0.2
-1.61
-0.322
Total 50
1.61 H’ E

17. 1 pi
lnpi
pilnpi 2 10
0.2
-1.61
-0.322 36
0.72
-0.329
-0.237 4
0.08
-2.53
-0.202 3
0.06
-2.81
-0.169
0.04
-3.22
-0.129
Total 50
1.61
0.938 H’ E

18. H’ E 1 pi lnpi pilnpi 2 3 10 0.2 -1.61 -0.322 36 0.72 -0.329 -0.237 -- 4
0.08
-2.53
-0.202 48
0.96
-0.04
0.06
-2.81
-0.169
0.04
-3.22
-0.129
Total 50
1.61
0.938
0.297 H’
0.362 E

19. Shannon Evenness Index
Shannon diversity index
natural logarithm
Total number of species

20. H’ E lnS = ln(5) = 1.61 lnS = ln(5) = 1.61 lnS = ln(3) = 1.098 1 pi
pilnpi 2 3 10
0.2
-1.61
-0.322 36
0.72
-0.329
-0.237
0.04 4
0.08
-2.53
-0.202 48
0.96
-0.04 -
0.06
-2.81
-0.169
-3.22
-0.129
Total 50
1.61
0.938
0.297 H’
0.362 E
1.0
0.583
0. 329
lnS = ln(5) = 1.61
lnS = ln(5) = 1.61
lnS = ln(3) = 1.098

21. Other measures of diversity
Simpson’s Diversity Index (D)
= 1/ ∑pi2
∑pi2 means the sum of the chances of finding each species in the community

22. Communities - Diversity
Often a single species can influence the structure
of an entire community
Keystone Species

23. Communities - Diversity
Since 1700’s

24. Communities - Diversity
- before hunting of sea otters
- after hunting of sea otters

25. Communities - Diversity
Keystone species

26. A second example – keystone species
California Mussel - Mytilus
Predatory seastar - Pisaster

27. A second example – keystone species
California Mussel - Mytilus
Predatory seastar - Pisaster

28. A second example – keystone species
1.5
Limit of mussel distribution above minimum tide
1.0
0.5
Time (Years)
Pisaster removal begins
Pisaster removal ends

29. Communities - Succession and Disturbance
What is “disturbance”?
Any event that changes a community, removes species from it or alters resource availability

30. Communities - Succession and Disturbance
Kinds of disturbance
Floods
Glaciers
Fire
Invasive species
Hurricane

31. Communities - Succession and Disturbance
Is disturbance always bad?? - Intermediate Disturbance
Hypothesis
Competition
reduces
community diversity
Frequent
disturbance
wipes out community
Diversity
Disturbance (frequency or intensity)

32. Communities - Succession and Disturbance
Replacement of species in a habitat through a regular progression
Usually after some disturbance

33. Communities - Succession and Disturbance
Primary Succession -
community is wiped out
to mineral rock
Secondary Succession - some soil or organic base left in community

34. Communities - Succession and Disturbance
Succession - Krakatoa - eruption in August, 1883
most of island was destroyed
sound heard 4500 km away
40m tsunami

35. Communities - Succession and Disturbance
Succession - Krakatoa
1886 -
6 species of
cyanobacteria
1890 -
11 species of ferns
1897 -
Tall grass prairie
1919 -
Scattered trees
1931 -
Fig tree woodland
1980 -
Rainforest
Primary succession
Secondary succession
1883

36. Communities - Succession and Disturbance
Succession - Krakatoa
Sea dispersed
Wind dispersed
Animal dispersed
Number of species
How did colonizers get there?

37. 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
Same kind of interaction (+/-)

38. 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