Download Ecology -Communities-

Ecology
-Communities-
Communities & Populations
•
Ways to characterize communities
Diversity
Keystone species
Disturbance and Succession
•
Processes at work in communities
Competition
Predation
Commensalism/mutualism
Community
- an assemblage of populations of various species
living close enough to potentially interact.
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
Communities - Diversity
Shannon Diversity index
natural logarithm
H’ = -Σ pi ln pi
Shannon
diversity index
Sum of
proportion of ith species
Communities - Diversity
Examples
- intertidal zone in New Brunswick
Sample and count
the number of each
species
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
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
1
Species 9
15
Species 10
4
Total = 200
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
1
0.005
Species 9
15
0.075
Species 10
4
0.02
Total = 200
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
.000025
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
1
0.005
.000025
Species 9
15
0.075
.00562
Species 10
4
0.02
.0004
Total = 200
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
1
0.005
-5.298
-0.026
Species 9
15
0.075
-2.59
-0.194
Species 10
4
0.02
-3.912
-0.078
Total = 200
H’ = 1.716
H’ = -Σ pi ln pi
If we remove the two most common species,
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
1
Species 9
15
Species 10
4
Total = 200
H’ = 1.774
(was 1.716)
Imagine a community that has (potentially) 5 species of tree
Look at 3 different forests
Forest 1
Forest 2
Forest 3
Forest 1
Forest 2
Forest 3
Total
H
E
1
2
3
10
36
0
10
4
48
10
4
0
10
3
2
10
2
0
50
50
50
Total
H’
E
1
pi
lnpi
pilnpi
10
0.2
-1.61
-0.322
10
0.2
-1.61
-0.322
10
0.2
-1.61
-0.322
10
0.2
-1.61
-0.322
10
0.2
-1.61
-0.322
50
1.61
1.61
Total
H’
E
1
pi
lnpi
pilnpi
2
pi
lnpi
pilnpi
10
0.2
-1.61
-0.322
36
0.72
-0.329
-0.237
10
0.2
-1.61
-0.322
4
0.08
-2.53
-0.202
10
0.2
-1.61
-0.322
4
0.08
-2.53
-0.202
10
0.2
-1.61
-0.322
3
0.06
-2.81
-0.169
10
0.2
-1.61
-0.322
2
0.04
-3.22
-0.129
1.61
50
50
1.61
0.938
0.938
1
pi
lnpi
pilnpi
2
pi
lnpi
pilnpi
3
pi
lnpi
pilnp
i
Total
H’
E
10
0.2
-1.61
-0.322
36
0.72
-0.329
-0.237
0
0
-
10
0.2
-1.61
-0.322
4
0.08
-2.53
-0.202
48
0.96
-0.04
10
0.2
-1.61
-0.322
4
0.08
-2.53
-0.202
0
0
-
10
0.2
-1.61
-0.322
3
0.06
-2.81
-0.169
2
0.04
-0.322
10
0.2
-1.61
-0.322
2
0.04
-3.22
-0.129
0
0
-
1.61
50
0.938
50
50
1.61
0.938
0.297
0.362
Shannon Evenness Index
Shannon
diversity index
H'
E
lnS
natural logarithm

Total number
of species
Total
1
pi
lnpi
pilnpi
2
pi
lnpi
pilnpi
3
pi
lnpi
10
0.2
-1.61
-0.322
36
0.72
-0.329
-0.237
2
0.04
-0.322
10
0.2
-1.61
-0.322
4
0.08
-2.53
-0.202
48
0.96
-0.04
10
0.2
-1.61
-0.322
4
0.08
-2.53
-0.202
0
0
-
10
0.2
-1.61
-0.322
3
0.06
-2.81
-0.169
2
0.04
-0.322
10
0.2
-1.61
-0.322
2
0.04
-3.22
-0.129
0
0
-
1.61
50
0.938
50
50
0.297
H’
1.61
0.938
0.362
E
1.0
0.583
0. 329
lnS = ln(5) = 1.61
lnS = ln(5) = 1.61
pilnpi
lnS = ln(3) = 1.098
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
Communities - Diversity
Often a single species can influence the structure
of an entire community
Keystone Species
Communities - Diversity
Since 1700’s
Communities - Diversity
- before hunting of sea otters
- after hunting of sea otters
Communities - Diversity
Keystone species
A second example – keystone species
California Mussel - Mytilus
Predatory seastar - Pisaster
A second example – keystone species
California Mussel - Mytilus
Predatory seastar - Pisaster
A second example – keystone species
1.5
Limit of mussel
distribution
above minimum
tide
1.0
0.5
0
2
4
6
8
10
Time (Years)
Pisaster removal begins
Pisaster removal ends
Communities - Succession and Disturbance
What is “disturbance”?
Any event that changes a community, removes
species from it or alters resource availability
Communities - Succession and Disturbance
Kinds of disturbance
Floods
Glaciers
Invasive
species
Fire
Hurricane
Communities - Succession and Disturbance
Is disturbance always bad?? - Intermediate Disturbance
Hypothesis
Diversity
Competition
reduces
community
diversity
Disturbance (frequency or intensity)
Frequent
disturbance
wipes out
community
Communities - Succession and Disturbance
Succession
Replacement of species in a habitat through
a regular progression
Usually after some disturbance
Communities - Succession and Disturbance
Succession
Secondary Succession - some
soil or organic base left in
community
Primary Succession community is wiped out
to mineral rock
Communities - Succession and Disturbance
Succession - Krakatoa - eruption in August, 1883
-most of island was destroyed
-sound heard 4500 km away
-40m tsunami
Communities - Succession and Disturbance
Succession - Krakatoa
1886 1890 6 species of 11 species
cyanobacteria of ferns
1897 Tall grass
prairie
Primary succession
1883
1919 Scattered
trees
1931 Fig tree
woodland
Secondary succession
1980 Rainforest
Communities - Succession and Disturbance
Succession - Krakatoa
Sea dispersed
Wind dispersed
Animal dispersed
Number
of
species
1860
1900
1940
How did colonizers get there?
1980
2000
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
+
0
Same kind
of
interaction
(+/-)
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
+
0