10/24/2013
Bio122 F13: Lecture 9 (10/24/13): Communities
Community Structure
I. Communities (Ch 15)
A. Defined
B. Food webs
II. Community structure
A. Species diversity
B. Measuring species diversity
1. Diversity indices
2. Rank abundance curves
3. Species accumulation curves
C. Species composition
III. Processes that shape community structure: Interactions
A. Direct & Indirect effects
1. Types of indirect effects
2. Interaction strength
3. Dominant species
4. Ecosystem engineers
5. Keystone species
IV. Community Succession(Ch 16)
A. Succession & its drivers
Functional diversity in coral reef
herbivores:
Impact upon ecosystem structure
Michelle Paddack
Predators
Herbivores
Resilience
?
Reef
Builders
University of East Anglia, Norwich UK
Simon Fraser University, BC Canada
X
NCORE
Grazing on coral reefs
Fishes
Number of species
Great Barrier Reef
Caribbean
Functional Group:
Species that perform
a similar role in
ecosystem processes,
irrespective of
taxonomic affinities
Bellwood et al. Nature 2004
• Macro-herbivores have
high grazing rates – 100 %
of daily algal production
• Algal communities in lowbiomass, highly-productive
states (algal turfs:
filamentous, < 1 cm tall)
• Macroalgal biomass
historically negligible
1
10/24/2013
Functional Groups: Herbivores
Scarids
(Parrotfishes)
13 spp.
Pomacentrids
(Damselfishes)
6 spp.
Urchins
(Diadema)
Acanthurids
(Surgeonfishes)
3 spp.
Are herbivorous fishes a
single functional group?
Kyphosids
(Chubs)
1 sp.
Acanthurus sp.
Purcell & Bellwood 1993
Scarus spp.
Sparisoma spp.
Bellwood & Choat 1990
Goals
1. Define herbivore functional sub-groups
2. Assign species to sub-groups
3. Determine whether correlations with
benthic variables differ among sub-groups
Methods:
Defining & designating Caribbean
herbivore functional sub-groups
(23 fish species)
Field observations:
Feeding behavior
Food preferences
Laboratory observations:
Randall 1967
Gut contents: type of algae
Gut contents: sediment
2
10/24/2013
bites minute-1
Grazing rate variation among
Caribbean herbivorous fishes
Photo by R. Steneck
40
35
30
25
20
15
10
5
0
1. Define herbivore functional sub-groups
Feeding strategies & ecosystem function
Diet
Disturbance
to benthos
Impact on coral
Browser
(Grazer)
Macroalgae
Very little sediment in gut
Low
- Crop algal
fronds
Reduce shading,
abrasion,
overgrowth
Scraper
Epilithic algal turf
& associated surface
sediment/detritus
High gut sediment content
Moderate
– Partial
clearing of
surface
Facilitate growth
& survival of CCA
& corals
Epilithic and endolithic
Excavator
(Bioeroder) algae & sediment/detritus
High
– Remove
substrate,
visible scar
Clear space for
CCA & coral
settlement
Eat coral recruits
Gardener
High/Patchy
– modify algal
community in
territories
No coral
recruitment in
territories
High gut sediment content
“Farmed” epilithic algae
& associated
sediment/detritus
Low gut sediment
Svir Saur Scroi Svet Abah
3. Examine sub-group correlations: Data
Atlantic & Gulf Rapid Reef Assessment
http://www.agrra.org/
Fish Counts:
30 x 2 m belt transect
Min. 10 per site
All Scarids (≥ 5 cm)
All Acanthurids
Microspathodon chrysurus
Sized in 5 cm bins
Excavators:
Scarus vetula
Sparisoma viride
Algal cover:
(original methodology)
25 x 25 cm quadrat
5 per transect
Target algal-covered area
% Cover Macroalgae
Algal height (avg)
# Coral Recruits (≤ 2cm)
AGRRA data:
Sub-country means
Fore reef, 3 – 9 m
Relative % Cover of Macroalgae
Costa Rica removed (1 site)
r2 = 0.278
p = 0.001
100
Rel % macroalgae
80
60
40
20
0
0
1
2
3
4
5
7
Total herbivore biomass (kg 100m-2)
100
80
60
40
20
6
r2 = 0.204
p = 0.006
80
60
40
20
0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Excavator biomass (kg 100m-2)
100
r2 = 0.117
p = 0.050
0
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Browser biomass (kg 100m-2)
80
r2 = 0.006
p = 0.687
60
40
20
0
0.0 0.1 0.2 0.3 0.4 0.5 0.6
Gardner biomass (kg 100m-2)
Rel % macroalgae
100
Rel % macroalgae
AGRRA
Fore reef sites (135)
15 countries
3 – 9 m depth
Rel % macroalgae
Gardeners:
Stegastes spp.
Microspathadon chrysurus
Scrapers:
Scarus coelestinus
Scarus guacamaia
Scarus taeniopteris
Scarus iserti
Scarus aurofrenatum
Acanthurus bahianus
Acanthurus chirurgus
Rel % macroalgae
Browsers:
Kyphosus sectatrix
Acanthurus coeruleus
Sparisoma chrysopterum
Sparisoma rubripinne
Scarus coeruleus
Sparisoma atomarium
Sparisoma radians
Crypototomus roseus
Significant
negative
correlations
for
Excavators
& Scrapers
100
80
60
r2 = 0.229
p = 0.004
40
20
0
0.0 0.5 1.0 1.5 2.0 2.5
Scraper biomass (kg 100m-2)
3
10/24/2013
Costa Rica removed (1 site)
Canopy height (mm)
0 1 2 3 4 5 6 7
Total herbivore biomass (kg 100m-2)
7
6
5
4
3
2
1
0
0.0
r2 = 0.125
p = 0.040
0.5
1.0
1.5
60
Significant negative
correlation for All Herbivores,
Excavators & Scrapers
2.0
7
6
r2 = 0.229
p = 0.004
5
4
3
2
1
0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Excavator biomass (kg 100m-2)
Fish biomass (kg m-2)
Functional group composition
relative to total biomass
1.8
Browser (8 spp.)
1.5
Excavator (2 spp.)
1.2
Scraper (7 spp.)
0.0
40
r2 = 0.002
p = 0.808
All herbivores:
N/S relationship
30
20
Significant positive
correlation for Excavators
10
0
2
4
6
8 10 12
Total herbivore biomass (g 100 m-2)
60
50
40
r2 = 0.270
p = 0.001
30
20
10
0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Excavator biomass (g 100m-2)
Findings:
• Few sites with high herbivore biomass in Caribbean
38%
• Herbivorous fishes are functionally diverse;
distinct sub-groups vary in impact on benthos
• Scrapers & excavators appear to have a particularly
strong impact
Gardener (6 spp.)
• Only 2 excavator species in the Caribbean
0.6
0.3
50
0
2.5
Scraper biomass (kg 100m-2)
0.9
AGRRA data:
Sub-country means
Fore reef, 3 – 9 m
% Live Coral Cover
% coral cover
r2 = 0.181
p = 0.012
AGRRA data:
Sub-country means
Fore reef, 3 – 9 m
% coral cover
7
6
5
4
3
2
1
0
Canopy height (mm)
Canopy height (mm)
Macroalgal canopy height
• Excavators decline quickly on heavily fished reefs
24%
< 1.1 (n=9)
• Low biodiversity -> vulnerability -> decreased resilience?
1.1 - 2 (n=8) 2.1 - 3 (n=11)
> 3 (n=7)
Total herbivorous fish biomass (kg m-2)
• To manage for resilience, need to
identify & focus on important &
vulnerable functional groups
St Thomas 2005
Photo: Jen Schull
Food chain
Trophic levels
Trophē = feed
4
10/24/2013
Rank Abundance Diagrams
Rank Abundance Diagrams
indicate differences in species richness & evenness
Birds of Great Lakes Basin
http://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.abstractDetail/abstract/7441/report/F
Species accumulation curve
5
10/24/2013
Foundation species
Important species
• Keystone species
– disproportionately large effect on its environment
relative to its abundance
Keystone Species
Oculina arbuscula
Elephants
Keystone species
Ochre star (Pisaster)
Sea otter
Community dynamics—
succession
Disturbance
•Humans can change
the flow of energy.
•Fishing down the
food web.
6
10/24/2013
Figure 16.5 A Theoretical Model of Succession
37
38
Community Succession and Species Richness
?
39
Study questions
1.
Define community
2.
Why is a community more than the sum of its
parts?
3.
Define guild.
4.
What is the difference between a trophic web and
an interaction web?
5.
Compare direct from indirect interactions.
6.
What is the difference between bottom-up and
top-down control within a food web?
7.
Describe a rank-abundance curve, noting what is
plotted along each axis. How would the curves differ for
communities with relatively higher vs. lower species
richness and for higher vs. lower species evenness? 41
Study questions
8.
What 2 pieces of information are used in
calculating species diversity (such as the Shannon index)?
9.
What would cause a community with low species
richness have a higher species diversity than another
community with higher species richness?
10. Define: foundation species, ecosystem engineer, &
keystone species. Provide an example of each.
11. Define succession. Provide an example of the steps
of succession in a community, being clear as to what
happens to allow each step to proceed into the next.
12. At what point in community succession is species
richness the greatest? Why?
42
7
10/24/2013
Study questions
13. What role does disturbance play in a community?
14. What is meant by “space for time substitution” of
succession?
15. Define alternate stable states and give an example.
43
8