Diversity and productivity The relationship between biodiversity and
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)?
How does productivity and variability depend on biodiversity (local scale)? P = f(S) s 2(P)=g(S) Darwin’s Wormestones
Biomass, Productivity, Enrgy turnover How does non-equilibrium population variability at the species level influence aggregate variables at the community level? Species and populations
The portfolio effect Year 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 CV A 791 734 588 298 129 575 10 703 711 947 834 357 712 970 522 B 724 801 880 72 549 656 426 706 729 294 244 530 961 889 464 C 165 833 486 685 590 2 557 387 429 971 7 71 312 328 889 D 623 170 232 56 782 740 648 649 199 37 582 221 236 477 973 E 446 566 826 682 775 655 692 744 397 22 537 771 59 376 579 F 896 845 251 625 622 103 292 128 780 625 764 237 906 424 Sum 607 658 544 403 574 455 437 553 532 509 472 453 419 657 642 0. 48 0. 43 0. 7 0. 66 0. 45 0. 52 0. 16 The coefficient of variation CV of a sum of random variates is smaller than single CVs.
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 < z < 2. 5 The decrease in variability follows a power function
Variance covariance of native savannah plantsatat. Cedar Creek in relation to species diversity. LTER –and Long term ecological research Creek, Minnesota 300000 y = 47800 Ln(x) - 115000 R 2 = 0. 33 200000 100000 0 -100000 Covariance y = 2 E+06 x R 2 = 0. 34 200000 100000 0 -100000 0 5 10 15 20 0 5 Number of species 60 50 40 30 20 y = 12. 8 Ln(x) + 11. 5 10 R 2 = 0. 96 0 0 10 20 Number of species 10 15 20 Number of species 120 samples from undisturbed native Minnesota grasslands. Total plant cover (%) 147 experimental plots at Cedar Creek in Minnesota Total plant cover (%) Variance -1. 85 100 80 60 40 20 y = 28. 6 Ln(x) - 10. 7 R 2 = 0. 77 0 0 10 20 Number of species
Results of the BIODEPTH experiment Aboveground -2 biomass [g m ] Grassland aboveground biomass depends on several factors among which locality, diversity and functional diversity are of major importance. 800 600 400 S=8 200 S=4 S = 11 0 0 1 2 3 Number of functional groups Grassland productivity declines as the number of functional groups decreases.
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
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: http: //biology. mcgill. ca/faculty/loreau/pdfs/loreauetalscience. pdf The Portfolio effect: www. ird. fr/ur 060/resultats/2002_Lhomme. Winkel_TPB. pdf
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