Function and diversity
The Portfoilio effect
Statistical averaging
David Tilman (1949-
Michel Loreau
𝐶𝑉 ∝
1
𝑆
If species act independent the coefficient of variation of aggregate ecosystem properties is
expected to decrease to the root of species richness.
Aggregate properties are particularly:
Biomass
Total abundance
Productivity
Assimilation
The law of the minimum and ecosystem functioning
Average performance
without limiting effects
Performance with
limiting effects
Species at minimum limit the functioning of ecosystem properties
𝐶𝑉 ∝
Point of
fast change
1
𝑆
Point of
fast change
Ecosystem
functioning
increases nonlineary with
species richness.
This model works if species form functional guilds whose members have equivalent properties.
The law of the minimum
Limiting factors:
Light
Water
Space
Nutrients
Water is the limiting factor for
photosynthetic rates with respect to
temperature
Temperature
Precipitation
Photosynthetic activity
Justus von Liebig
(1803-1873)
Euryoecious organisms
tolerate a wider range of
habitat conditions.
Stenoecious organisms have
limited tolerance.
– Longofterm
ecological
research
at Cedar
Minnesota
Variance andLTER
covariance
native
savannah plants
at Cedar
CreekCreek,
in relation
to species diversity.
147 experimental plots at
Cedar Creek in Minnesota
120 samples from undisturbed native
Minnesota grasslands.
Tilman 1999,
Ecology 80:
1455-1474
100
50
40
30
20
y = 12.8Ln(x) + 11.5
10
R 2 = 0.96
0
Total plant cover (%)
Total plant cover (%)
60
80
60
40
20
y = 28.6Ln(x) - 10.7
R 2 = 0.77
0
0
10
20
Number of species
0
10
20
Number of species
Results of the BIODEPTH experiment
Source of variation
Locality
Species richness
Functional group richness
Assemblage
Locality x Assemblage
Residual
Total
SS
12.4
6.6
1.17
17.1
2.08
4.46
43.81
% SS
28.3%
15.1%
2.7%
39.0%
4.7%
10.2%
F
24.7
7.15
6.34
1.29
3.77
p
< 0.00001
< 0.00001
0.002
0.2
< 0.00001
Grassland aboveground biomass depends on several factors among which locality,
diversity and functional diversity are of major importance.
Hector et al. 1999,
Science 286, 1123-1127
Grassland productivity declines as the number of functional groups decreases.
z
z
Biodiversity and bacterial activity
30
Bacterial respiration
Bacterial respiration
30
25
20
15
10
5
28 days experimental time
0
25
Day 0-7
20
15
Day 7-14
10
5
Day 14-28
0
0
20
40
60
Species richness
80
0
20
40
60
80
Species richness
Bell et al. 2005, Nature 436: 1157-1160
Bacterial species richness influences respiration of soils from beech stands.
Respiration is not a linear function of bacterial richness
This points to the existence of redundant species
The current state of art:
• Ecosystem functioning depends not such much on species richness but
on richness of functional groups (ecologigal guilds)
• Productivity increases with plant functional group richness
• Stability increases with plant functional group richness
• Drought restistance increase with plant functional group richness
• Bacterial species richness promotes efficiency of bacterial services like
breakdown of pollutants
• Decomposition increases with eukaryotic species richness
• Total bacterial activity increases with bacterial foodweb complexity
• Stability decreases with dispersal among patches
• Habitat fragmentation and species richness act synergistically and
decrease stability
How do diversity and stability depend on productivity?
Species richness peaks often at intermediate productivity
250
Palearctic birds
Evapotranspiration is the sum of
evaporation and transpiration,
hence the total amount of water
going from living organismas and
the soil into the atmosphere.
200
S
150
100
50
It is a measure of total energy
input.
0
0
500
1000
Evapotranspiration
1500
Hawkins et al. 2003, Ecology 84: 3105-3117
250
Palearctic butterflies
200
150
S
Species richness often
peaks at intermediate
degrees of
evapotransiration.
100
50
0
0
500
1000
Evapotranspiration
1500
Hawkins et al. 2003, Ecology 84: 3105-3117
Bird species numbers are correlated with annual evapotranspiration and temperature.
The influence of productivity on the species richness of plants
z
80
Percent
100
60
Continental scale
40
20
0
Humped
Positive Negative
Ushaped
None
z
80
Percent
100
60
Regional
40
20
0
Humped
Positive Negative
Ushaped
None
z
Percent
100
80
60
Local scale
40
20
Gillman, Wright, 2006,
Ecology 87: 1234-1243
Meta-analysis found
very variable
patterns of the
productivity species
richness
relationship at local
scales.
0
Humped
Positive Negative
Ushaped
None
Above the local
scale plant species
richness increases
with productivity.
Patterns of fish species richness in China’s lakes
Zhao et al. 2006,
Gl. Ecol.
Biogeogr.
2
R = 0.75
S
S
140
120
100
80
60
40
20
0
1
10
100
1000
140
120
100
80
60
40
20
0
10000
2
R = 0.34
1
140
120
100
80
60
40
20
0
0.001
0.1
100
1000
Maximum depth [m]
S
S
Altitude [m]
10
10
1000
8
3
Lake volume [10 m ]
140
120
100
80
60
40
20
0
0.1
10
1000
100000
2
Lake area [km ]
Fish species richness scales significantly with altitude and maximum depth of a lake
Lake volume is of minor importance
1000
1000
2
2
R = 0.43
R = 0.57
100
S
S
100
10
10
1
1
-10
0
10
20
30
0
1000
1500
Annual potential
evapotranspiration [mm]
Mean annual temperature
1000
500
1000
2
2
R = 0.53
R = 0.40
100
S
S
100
10
10
1
1
0
500
1000
Annual actual
evapotranspiration [mm]
0
500
1000
1500
2000
Annual precipitation [mm]
Main determinants of fish species richness were annual PET, altitude, and
lake area.
Productivity and stability
Are tropical populations more stable than populations in temperate or arctic regions?
5
CV
4
3
2
1
0
0
20
40
60
80
There is no general latitudinal trend in
population variability
Taxon
Hemiptera
Hymenoptera
Lepidoptera
Falconiformes
Galliformes
Passeriformes
Strigiformes
Artiodactyla
Carnivora
Insectivora
Lagomorpha
Rodentia
r
0.01
-0.72
-0.37
-0.85
0.22
-0.28
0.7
0.21
0.71
-0.09
-0.99
0.32
P
>0.1
<0.01
<0.001
<0.01
>0.1
<0.01
>0.1
>0.1
<0.01
>0.1
<0.001
<0.01
Vazquez, Stevens, 2004, Am. Nat 164: E1-E19
CV
Latitude
5
4
3
2
1
0