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)?

Darwin’s Wormestones How does productivity and variability depend on biodiversity (local scale)? P = f(S)   (P)=g(S)

Species and populations Biomass, Productivity, Enrgy turnover How does non-equilibrium population variability at the species level influence aggregate variables at the community level?

The portfolio effect YearABCDEFSum CV The coefficient of variation CV of a sum of random variates is smaller than single CVs.

For 1 species: If no species interactions cov (i,j) = 0: The portfolio effect For S species: The variability of aggregate variables should decrese with increasing species diversity The majority of species has 1.5 < z < 2.5 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) The decrease in variability follows a power function David Tilman (1949-

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) R 2 = Number of species Total plant cover (%) y = 28.6Ln(x) R 2 = Number of species Total plant cover (%) LTER – Long term ecological research at Cedar Creek, Minnesota

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 Number of functional groups Aboveground biomass [g m -2 ] S = 8 S = 11 S = 4

Biodiversity and bacterial activity (Bell et al. 2005) 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 Day 7-14

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

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

Today’s reading Biodiversity and ecoystem functioning: The Portfolio effect: