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Function and diversity
David Tilman (1949-
The Portfoilio effectStatistical averaging
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:BiomassTotal abundanceProductivityAssimilation
Michel Loreau
The law of the minimum and ecosystem functioning
Species at minimum limit the functioning of ecosystem properties
Point of fast change
Ecosystem functioning increases non-lineary with species richness.
This model works if species form functional guilds whose members have equivalent properties.
Point of fast change
Average performance without limiting effectsPerformance with limiting effects
𝐶𝑉 ∝1
√𝑆
The law of the minimum
Justus von Liebig (1803-1873)
Euryoecious organisms tolerate a wider range of
habitat conditions.Stenoecious organisms have
limited tolerance.
Limiting factors:LightWaterSpaceNutrients
Phot
osyn
theti
c ac
tivity
Temperature
Precipitation
Water is the limiting factor for photosynthetic rates with respect to
temperature
Variance and covariance of native savannah plants at Cedar Creek in relation to species diversity.
147 experimental plots at Cedar Creek in Minnesota
120 samples from undisturbed native Minnesota grasslands.
y = 12.8Ln(x) + 11.5R 2 = 0.96
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0 10 20Number of species
Tota
l pla
nt c
over
(%)
y = 28.6Ln(x) - 10.7R 2 = 0.77
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0 10 20Number of species
Tota
l pla
nt c
over
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LTER – Long term ecological research at Cedar Creek, Minnesota
Tilman 1999, Ecology 80: 1455-1474
Grassland aboveground biomass depends on several factors among which locality, diversity and functional diversity are of major importance.
Results of the BIODEPTH experiment
Grassland productivity declines as the number of functional groups decreases.
Hector et al. 1999, Science 286, 1123-1127
Source of variation SS % SS F pLocality 12.4 28.3% 24.7 < 0.00001Species richness 6.6 15.1% 7.15 < 0.00001Functional group richness 1.17 2.7% 6.34 0.002Assemblage 17.1 39.0% 1.29 0.2Locality x Assemblage 2.08 4.7% 3.77 < 0.00001Residual 4.46 10.2%Total 43.81
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Species richness
Ba
cte
rial r
esp
iratio
n
z
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0 20 40 60 80
Species richness
Ba
cte
rial r
esp
iratio
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Biodiversity and bacterial activity
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
28 days experimental time
Day 0-7
Day 14-28
Day 7-14
Bell et al. 2005, Nature 436: 1157-1160
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
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0 500 1000 1500Evapotranspiration
S
Palearctic birds
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0 500 1000 1500Evapotranspiration
SPalearctic butterflies
Evapotranspiration is the sum of evaporation and transpiration, hence the total amount of water going from living organismas and the soil into the atmosphere.
It is a measure of total energy input.
Hawkins et al. 2003, Ecology 84: 3105-3117
Species richness often peaks at intermediate degrees of evapotransiration.
Bird species numbers are correlated with annual evapotranspiration and temperature.
Hawkins et al. 2003, Ecology 84: 3105-3117
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Humped Positive Negative U-shaped
None
Pe
rce
nt
z
Continental scale
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Humped Positive Negative U-shaped
None
Pe
rce
nt
z
Regional
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Humped Positive Negative U-shaped
None
Pe
rce
nt
z
Local scale
Gillman, Wright, 2006, Ecology 87: 1234-1243
The influence of productivity on the species richness of plants
Meta-analysis found very variable patterns of the productivity species richness relationship at local scales.
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.
Fish species richness scales significantly with altitude and maximum depth of a lake
Lake volume is of minor importance
020406080
100120140
1 10 100 1000 10000
Altitude [m]
S
R2 = 0.75
020406080
100120140
1 10 100 1000
Maximum depth [m]
S
R2 = 0.34
020406080
100120140
0.001 0.1 10 1000
Lake volume [108 m3]
S
020406080
100120140
0.1 10 1000 100000
Lake area [km2]
S
Main determinants of fish species richness were annual PET, altitude, and lake area.
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1000
-10 0 10 20 30
Mean annual temperature
S
R2 = 0.43
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1000
0 500 1000 1500
Annual potential evapotranspiration [mm]
S
R2 = 0.57
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100
1000
0 500 1000Annual actual
evapotranspiration [mm]
S
R2 = 0.53
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1000
0 500 1000 1500 2000
Annual precipitation [mm]
S
R2 = 0.40
Productivity and stability
Are tropical populations more stable than populations in temperate or arctic regions?
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0 20 40 60 80Latitude
CV
Taxon r PHemiptera 0.01 >0.1Hymenoptera -0.72 <0.01Lepidoptera -0.37 <0.001Falconiformes -0.85 <0.01Galliformes 0.22 >0.1Passeriformes -0.28 <0.01Strigiformes 0.7 >0.1Artiodactyla 0.21 >0.1Carnivora 0.71 <0.01Insectivora -0.09 >0.1Lagomorpha -0.99 <0.001Rodentia 0.32 <0.01
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0 20 40 60 80
CV
There is no general latitudinal trend in population variability Vazquez, Stevens, 2004, Am. Nat 164: E1-E19
