Slajd 1

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Diversity and productivity

• The relationship between biodiversity and
  productivity has four different aspects
• How does productivity depend on biodiversity
  (local scale)?
• How does temporal variability influence
  productivity (local scale)?
• How does biodiversity depend on productivity
  (regional scale)?
• How does productivity influence temporal
  variability (regional scale)?

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How does productivity and variability depend on
biodiversity (local scale)?
P f(S) s2(P)g(S)
Darwins Wormestones
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How does non-equilibrium population variability
at the species level influence aggregate
variables at the community level?
Biomass, Productivity, Enrgy turnover
Species and populations
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The portfolio effect
Assume we have S species that fluctuate
independently in time. Assume further an aggegate
variable that is the sum of single species values
(f. i. biomass, total assimilation, energy use)
David Tilman (1949-
For 1 species
For S species
If no species interactions cov (i,j) 0
The variability of aggregate variables should
decrese with increasing species diversity
The majority of species has 1.5 lt z lt 2.5
The decrease in variability follows a power
function
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A patch occupancy simulation of the dependence of
CV on species diversity corroborates the above
model of Tilman and shows a more or less
pronounced threshold effect.
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Yield effect
?i mean density of species I S Total number of
species m a constant measuring biomass x a
yield coefficient.
Total community biomass depends according to
Tilmans theory on the number of species and a
specific yield coefficient that relates total
biomass to species interactions, B Relating this
yield coefficient to the parameter z of Taylor
power law shows that only at z-values and high
yield coefficients higher diversity will
destabilize communities.
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LTER Long term ecological research at Cedar
Creek, Minnesota
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.
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Results of the BIODEPTH experiment
Grassland aboveground biomass depends on several
factors among which locality, diversity and
functional diversity are of major importance.
Grassland productivity declines as the number of
functional groups decreases.
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Biodiversity and bacterial activity (Bell et al.
2005)
Day 0-7
Day 7-14
28 days experimental time
Day 14-28
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
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Ecosystem functioning and dispersal

• Eelgras crustacean grazer marine mesocosms
  systems (France and Duffy 2006)
• Dispersal increases the variability of ecosystem
  services
• Species richness at low dispersal decreases the
  variablity of ecosystem services
• Species richness at high dispersal increases the
  variablity of ecosystem services
• Habitat fragmentation and decrease in species
  richness act synergistically on ecosystem
  stability

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• 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
• Bacterial activity increases with foodweb
  complexity
• Stability decreases with dispersal among patches
• Habitat fragmentation and species richness act
  synergistically and decrease stability

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Todays reading
Biodiversity and ecoystem functioning
http//biology.mcgill.ca/faculty/loreau/pdfs/lorea
uetalscience.pdf The Portfolio effect
www.ird.fr/ur060/resultats/2002_LhommeWinkel_TPB.p
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