COMMUNITY STRUCTURE

1
Lecture 10 COMMUNITY STRUCTURE
2
Community Structure
Paine 80 - Keystone Species
Keystone species -a relatively low biomass
species that is a major factor in determining
community structure
3
Community Structure
Paine 80 - Keystone Species
Introduced concept of links in community
e.g. Pisaster and Mytilus
Pisaster
Tonicella
Katherina
Mytilus
Lithophyllum
Hedophyllum
4
Community Structure
Paine 80 - Keystone Species
Introduced concept of links in community
e.g. Pisaster and Mytilus
strong link
weak links
Pisaster
Tonicella
Katherina
Mytilus
Lithophyllum
Hedophyllum
5
Community Structure
Paine 80 - Keystone Species
Introduced concept of links in community
e.g. Pisaster and Mytilus
strong link
weak links
Pisaster
Tonicella
Katherina
Mytilus
Lithophyllum
Hedophyllum
Module 1
Module 2
6
Keystone species
Enhydra lutris
Strongylocentrotus purpuratus
Macrocystis pyrifera
7
But in reality - much more complex
8
But in reality - VERY much more complex
9
Another take on this - Menge and Sutherland 87
Food Web
Rat
Gulls
Fish
Crabs
Sea stars
Limpet
Snails
Whelk
Urchin
Red algae
Barnacles
Crusts
Emphemerals
Polychaete
Bivalves
10
Another take on this - Menge and Sutherland 87
Interaction web
Rat
Gulls
strong links
Fish
weak links
Crabs
Sea stars
Limpet
Snails
Whelk
Urchin
Red algae
Barnacles
Crusts
Emphemerals
Polychaete
Bivalves
11
Interactions between species in an intertidal
community
Can be looked at in one of two ways
a) Hierarchy
A
A
A
C
B
C
A
B
B
C
b) Network
B
A
A
C
C
C
B
B
C
A
A
B
Time
12
Community Structure
Multispecies interactions - Underwood
Patelloida -acamaeid limpet
Tesseropora - barnacle
Morula - predatory whelk
Cellana - patellid limpet
13
Community Structure
Multispecies interactions - Underwood
Exclusion cages
14
Community Structure
Multispecies interactions - Underwood
Experiment 1 - Effect of Cellana on survival of
Tesseropa
Morula - excluded
Tesseropora
Cellana -grazes open rock
15
Community Structure
Multispecies interactions - Underwood
Experiment 1 - Effect of Cellana on survival of
Tesseropa
Higher survivorship at intermediate density
Tesseropora surviving
0 2 4 6 8 10
Cellana/enclosure
16
Community Structure
Multispecies interactions - Underwood
Experiment 2 - Effect of Tesseropa on growth of
Cellana
Cellana growth rate
Tesseropa density
17
Community Structure
Multispecies interactions - Underwood
Experiment 2 - Effect of Tesseropa on growth of
Cellana
Experiment 2 - Effect of Tesseropa on growth of
Patelloida
Cellana growth rate
Patelloida growth rate
Tesseropa density
18
Community Structure
Multispecies interactions - Underwood
General conclusion - major interactions among
all components of system - no keystone species
- no links are weak
19
Community Structure
How do the forces shaping communities
interact? (Menge and Sutherland, Amer. Nat.
110351)
-consider situations of a) high and low
stress b) high and low recruitment
Habitat amelioration
Relative importance
high
low
Stress
HIGH RECRUITMENT
20
Community Structure
How do the forces shaping communities
interact? (Menge and Sutherland, Amer. Nat.
110351)
-consider situations of a) high and low
stress b) high and low recruitment
Habitat amelioration
Relative importance
Competition
high
low
Stress
HIGH RECRUITMENT
21
Community Structure
How do the forces shaping communities
interact? (Menge and Sutherland, Amer. Nat.
110351)
-consider situations of a) high and low
stress b) high and low recruitment
Habitat amelioration
Predation
Relative importance
Competition
high
low
Stress
HIGH RECRUITMENT
22
Community Structure
How do the forces shaping communities
interact? (Menge and Sutherland, Amer. Nat.
110351)
-consider situations of a) high and low
stress b) high and low recruitment
Habitat amelioration
Predation
Relative importance
Competition
Associational defenses
high
low
Stress
HIGH RECRUITMENT
23
Community Structure
How do the forces shaping communities
interact? (Menge and Sutherland, Amer. Nat.
110351)
-consider situations of a) high and low
stress b) high and low recruitment
Relative importance
Competition
high
low
Stress
LOW RECRUITMENT
24
Community Structure
How do the forces shaping communities
interact? (Menge and Sutherland, Amer. Nat.
110351)
-consider situations of a) high and low
stress b) high and low recruitment
Predation
Relative importance
Competition
high
low
Stress
LOW RECRUITMENT
25
Community Structure
How do the forces shaping communities
interact? (Menge and Sutherland, Amer. Nat.
110351)
-consider situations of a) high and low
stress b) high and low recruitment
Predation
Relative importance
Competition
Associational defenses
high
low
Stress
LOW RECRUITMENT
26
Community Structure
How do the forces shaping communities
interact? (Menge and Sutherland, Amer. Nat.
110351)
-consider situations of a) high and low
stress b) high and low recruitment
Predation
Habitat amelioration
Relative importance
Competition
Associational defenses
high
low
Stress
LOW RECRUITMENT
27
Community Structure
Relationship to diversity
Diversity
high
low
Stress
28
Community Structure
Relationship to diversity
Negative effects of competition and predation
Negative effects of stress
Diversity
high
low
Stress
29
Community Structure
Disturbance and Diversity Connell - Intermediate
Disturbance Hypothesis
Diversity
Low High
Disturbance (frequency, intensity, extent)
30
Community Structure
Disturbance and Diversity Connell - Intermediate
Disturbance Hypothesis
Competitive dominants fill space
Diversity
Low High
Disturbance (frequency, intensity, extent)
31
Community Structure
Disturbance and Diversity Connell - Intermediate
Disturbance Hypothesis
Competitive dominants fill space
Few species can invade or persist
Diversity
Low High
Disturbance (frequency, intensity, extent)
32
Models of succession

• Inhibition
• initial colonizers inhibit future colonizers.

• 2. Tolerance
• initial colonizers do not affect later
  colonizers. Organisms best suited to local
  conditions will persist (e.g. Chthalamus/Semibalan
  us)

• 3. Facilitation
• initial colonizers facilitate success of later
  colonizers (e.g. protection of barnacles
  growth of algae

33
Models of succession -probably work in
different areas
Habitat stress Recruitment
Inhibition low high
Tolerance midrange low
Facilitation high high or low
34
Community Structure Top-Down vs. Bottom-Up
Control
35
Hairston, Smith and Slobodkin (1960)
Community Dynamics
Carnivores
Detritivores
control
Resource limited
Frees plants from herbivore control
Herbivores
Plants
36
Critiques
Too Simple
1) Species differences matter
2) Plant dominance could be explained by good
defences
37
Other inferences of Hairston et al, 1960
??
1) Exceptions not important
X
2) All communities have 3 trophic levels
3) Omnivory not important
X
4) External abiotic factors - not controllers
X
38
Robles et al, 1995
Mean Density (seastars/m2)
Recruitment index of Mytilus
39
Menge and Sutherland, 1976
Effects of predation by whelks.
Predation is weak
High wave energy - effects of predation -weak
Moderate wave energy - effects of predation
- strong
Menge
Sutherland
40
Ecological Relationships in Kelp Forests
Orca
Kelp
Sea Otter
Urchins
41
Bottom Up Control
Fretwell, 1977, 1987
- availability of plant material governs
structure of food chains
- Low productivity - 1 link (plants)
- Higher productivity - add links
42
Transplant mussels and barnacles (filter feeders)
to urchin-dominated and kelp-dominated substrates
43
Transplant mussels and barnacles (filter feeders)
to urchin-dominated and kelp-dominated substrates
Expected (top down)
Urchin - dominated
Kelp - dominated
44
Transplant mussels and barnacles (filter feeders)
to urchin-dominated and kelp-dominated substrates
Expected (top down)
Observed (bottom up)
Urchin - dominated
Kelp - dominated
Urchin - dominated
Kelp - dominated
45
Clearly - can be a complex interaction
Increased nutrient
Increased algae
Increased benthic filter feeders
Increased consumers (predation)
control
46
Interaction of Systems
High flow
Low flow
Leonard et al, 1998
47
Interaction of Systems
increased seaweed growth
increased filter feeder growth
increased consumer pressure
increased larval settlement
increased sedimentation
low consumer efficiency
lower densities of organisms with planktonic
larvae
higher densities of organisms with planktonic
larvae
increased consumer mortality
more spatial competition
less spatial competition
48
Leonard et al, 1998
Hydrodynamics
Flow rate
Time
49
Leonard et al, 1998
Community structure
High flow
Low flow
Tide height
Percent cover
Percent cover
barnacles
Fucus
mussels
Bare space
50
Leonard et al, 1998
High flow
Recruitment rates
Low flow
Barnacles Mussels Snails
Density (/100 cm2)
51
Leonard et al, 1998
Crab predation
High flow
Low flow
On Littorina, Nucella, Mytilus
Predation Intensity ( mortality)
52
Leonard et al, 1998
crabs
grazers
mussels
barnacles
diatoms
Nutrients
Larvae
Plankton
53
Leonard et al, 1998
crabs
crabs
whelks
grazers
grazers
mussels
barnacles
mussels
barnacles
diatoms
diatoms
Nutrients
Nutrients
Larvae
Larvae
Plankton
Plankton
54
Interference competition, exploitative
competition for resources other than food
Depletion of more nutritious, palatable or
accessible prey
(-)
Predators
(-)
(-)
- ()
Induced morphological or chemical defenses,
hiding, retreat to refuges
Consumers
(-)
Cover from (for) predators
Stimulation of area-specific primary productivity
Plants
()
Powers. 92. Ecology 73 733