Dutkiewicz, S.

Follows, M.

Oschlies, Andreas

Pahlow, Markus

Prowe, Friederike

English

OceanRep

!"#$%&'$$(")*&+,-.,$*"$+&.)(&/0$1"+,$)/$&&")&.&&/023$445$&3-$(.40)&20($6&&!"#$%$"#&$'(")*$'+,"&-.'(,/0)*1'23%"$,.'4.5/0#$.'67$8/',3%'+#5&'99:;<:=;9;' Top-down control of biodiversityFriederike Prowe1, Markus Pahlow1, Stephanie Dutkiewicz2,Mick Follows2, Andreas Oschlies11IFM-GEOMAR, Kiel, Germany, 2MIT, Cambridge, MA, USA!"#$%&'$$(")*&+,-.,$*"$+&.)(&/0$1"+,$)/$&&")&.&&/023$445$&3-$(.40)&20($6&&!"#$%$"#&$'(")*$'+,"&-.'(,/0)*1'23%"$,.'4.5/0#$.'67$8/',3%'+#5&'99:;<:=;9;'Phytoplankton diversity in ecosystem modelsEcosystem stability and functioning are influenced by community composition and biodiversity. Ecosystemmodels have tried to resolve diversity by including multiple nutrients and different phytoplankton functionaltypes. These bottom-up approaches seem to considerably underestimate observed phytoplankton diversity.Here we investigate the effects of top-down control by zooplankton grazing on diversity.Zooplankton grazing in models• each zoo has a different preference for each phyto type (size, edibility, nutritional value, ...)a) constant preferences: independent of phyto type concentration (no switching)b) variable selectivity calculated from preferences and concentration: zoo prefer to graze most abundanttypes (active switching)• experimental observations of active switching exist for microzooplankton and copepods• our interpretation: switching as parameterization of the zooplankton community response:one resource type increases⇒ predator specialized on that resource increases; and vice versaThe model•Darwin & MITgcm 3D coupled physical-biogeochemical•NPZD-type, 10 year simulations• 78 phytoplankton types with random nutrient require-ments, growth and sinking parameters• 2 zooplankton (small & large) with type II grazing(saturates with phyto concentration P )• self-assembling phytoplankton communityThis study• no switching vs. active switching• low and high grazing rates I78 Phytodiff. growth, sinking2 Zoosmall & largePOMDOMexportNO2, NH4NO3, PO4, Si, FePredation increases diversity• low grazing, no switching (LGNS;standard run):lower than observed diversity(see Simulations vs. Observations)•with switching (LGAS):diversity increases by 82%• high grazing, no switching (HGNS):diversity decreases• high grazing and switching (HGAS):even larger diversity increasecloser to observations⇒ with switching, grazing pressure in-creases with concentration:stronger negative feedback by grazingthan without switching(see Grazing pressure at right)Annual average phytoplankton diversity (numberof species above threshold concentration, 0-55 m)for low grazing & no switching (LGNS, standardrun), low grazing & active switching (LGAS; star:NABE, dots: AMT), high grazing & no switching(HGNS), high grazing & active switching (HGAS).Grazing pressure in a 2-phytoplankton systemr = 2 phyto types with equal preferences: ρ1 = ρ2 = 0.5concentrations phyto 1 (P1) increases, phyto 2 (P2) constantPreference/selectivity• no switching:σj = ρj = 0.5 , j = 1, 2• switching: selectivity σjσj =ρjPj∑r ρrPrincreases for phyto 1decreases for phyto 20 0.002 0.004 0.006 0.008 0.0100.20.40.60.81P1 concentrationpreference or selectivity  ρ1 ρ2 σ1 σ2Specific grazing pressureIj/Pj = gmaxσjkκP+∑r σrPr• no switching:I/P decreases slightly forboth phyto 1 and phyto 2• switching:I/P increases for phyto 1,decreases for phyto 2⇒ most abundant phytotype preferred0 0.002 0.004 0.006 0.008 0.010102030spec. grazing pressure I j/P j  P1 HGNS P2 HGNS P1 HGAS P2 HGASP1 concentrationP1 LGNS P2 LGNS P1 LGAS P2 LGASThe seasonal cycle at NABEno switching (LGNS) switching (HGAS)Phytoplankton dynamics at the North Atlantic Bloom Experiment(NABE) site for LGNS (left) and HGAS (right). (A) Average totalphyto concentration (0-55 m) compared to observations (circles).Averages (0-55 m) for all phyto types present of (B) growth (nutrientuptake minus sinking minus mortality), (C) growth minus grazing,and (D) total grazing pressure by both zoo types, (E) concentration.• 1 bloom peak instead of 2 observed (A) with 1 large (L2) and 1 small (S1) phyto type• types with highest growth (B) and winter biomass (E) dominate• grazing pressure between types differs only in magnitude (different, but constant preferences),increases simultaneously for all types (D)• thus growth minus grazing also decreases simultaneously (C)• 2 bloom peaks as in the observations (A), with high diversity (E)• growth minus grazing decreases at different times for phyto types of 1. and 2. peak (C)• types with high growth (B) and high winter biomass (E) dominate 1. peak• types with low growth (B) and lower grazing pressure than other types form 2. peak⇒ phytoplankton successionSimulations vs. Observations along the AMT• observations: no latitudinal diversity gradient• LGNS, HGNS: diversity gradient: maximum at low lati-tudes, lower at high latitudes• LGAS, HGAS: no diversity gradient⇒ results with switching (LGAS, HGAS) fit the observedrange and latitudinal pattern better than with no switch-ing (LGNS, HGNS)Simulated annual average diversity (Shannon Index) in the surfacelayer along the Atlantic Meridional Transect (AMT) compared to ob-servations (circles; after Irigoien et al. 2004) for LGNS, HGNS, LGASand HGAS.Summary & OutlookEffects of predation on phytoplankton diversity in ecosystem models:• predation increases diversity when a zooplankton community responseis included e.g. by active switching (zooplankton have variable,concentration-dependent selectivity for different phyto types)With switching:• simulated diversity agrees better with observed latitudinal diversity pattern•more realistic bloom dynamics at NABE• succession and coexistence of different phyto typesWhat’s next:assess the role of phytoplankton diversity for the functioning of the marineecosystem under environmental changeClimECO2 summer school, 23–27 August 2010, Brestfprowe@ifm-geomar.de

Top-down control of biodiversity

!"#$%&'$$(")*&+,-.,$*"$+&.)(&/0$1"+,$)/$&&")&.&&/023$445$&3-$(.40)&20($6&&!"#$%$"#&$'(")*$'+,"&-.'(,/0)*1'23%"$,.'4.5/0#$.'67$8/',3%'+#5&'99:;<:=;9;' Top-down control of biodiversityFriederike Prowe1, Markus Pahlow1, Stephanie Dutkiewicz2,Mick Follows2, Andreas Oschlies11IFM-GEOMAR, Kiel, Germany, 2MIT, Cambridge, MA, USA!"#$%&'$$(")*&+,-.,$*"$+&.)(&/0$1"+,$)/$&&")&.&&/023$445$&3-$(.40)&20($6&&!"#$%$"#&$'(")*$'+,"&-.'(,/0)*1'23%"$,.'4.5/0#$.'67$8/',3%'+#5&'99:;<:=;9;'Phytoplankton diversity in ecosystem modelsEcosystem stability and functioning are influenced by community composition and biodiversity. Ecosystemmodels have tried to resolve diversity by including multiple nutrients and different phytoplankton functionaltypes. These bottom-up approaches seem to considerably underestimate observed phytoplankton diversity.Here we investigate the effects of top-down control by zooplankton grazing on diversity.Zooplankton grazing in models• each zoo has a different preference for each phyto type (size, edibility, nutritional value, ...)a) constant preferences: independent of phyto type concentration (no switching)b) variable selectivity calculated from preferences and concentration: zoo prefer to graze most abundanttypes (active switching)• experimental observations of active switching exist for microzooplankton and copepods• our interpretation: switching as parameterization of the zooplankton community response:one resource type increases⇒ predator specialized on that resource increases; and vice versaThe model•Darwin & MITgcm 3D coupled physical-biogeochemical•NPZD-type, 10 year simulations• 78 phytoplankton types with random nutrient require-ments, growth and sinking parameters• 2 zooplankton (small & large) with type II grazing(saturates with phyto concentration P )• self-assembling phytoplankton communityThis study• no switching vs. active switching• low and high grazing rates I78 Phytodiff. growth, sinking2 Zoosmall & largePOMDOMexportNO2, NH4NO3, PO4, Si, FePredation increases diversity• low grazing, no switching (LGNS;standard run):lower than observed diversity(see Simulations vs. Observations)•with switching (LGAS):diversity increases by 82%• high grazing, no switching (HGNS):diversity decreases• high grazing and switching (HGAS):even larger diversity increasecloser to observations⇒ with switching, grazing pressure in-creases with concentration:stronger negative feedback by grazingthan without switching(see Grazing pressure at right)Annual average phytoplankton diversity (numberof species above threshold concentration, 0-55 m)for low grazing & no switching (LGNS, standardrun), low grazing & active switching (LGAS; star:NABE, dots: AMT), high grazing & no switching(HGNS), high grazing & active switching (HGAS).Grazing pressure in a 2-phytoplankton systemr = 2 phyto types with equal preferences: ρ1 = ρ2 = 0.5concentrations phyto 1 (P1) increases, phyto 2 (P2) constantPreference/selectivity• no switching:σj = ρj = 0.5 , j = 1, 2• switching: selectivity σjσj =ρjPj∑r ρrPrincreases for phyto 1decreases for phyto 20 0.002 0.004 0.006 0.008 0.0100.20.40.60.81P1 concentrationpreference or selectivity  ρ1 ρ2 σ1 σ2Specific grazing pressureIj/Pj = gmaxσjkκP+∑r σrPr• no switching:I/P decreases slightly forboth phyto 1 and phyto 2• switching:I/P increases for phyto 1,decreases for phyto 2⇒ most abundant phytotype preferred0 0.002 0.004 0.006 0.008 0.010102030spec. grazing pressure I j/P j  P1 HGNS P2 HGNS P1 HGAS P2 HGASP1 concentrationP1 LGNS P2 LGNS P1 LGAS P2 LGASThe seasonal cycle at NABEno switching (LGNS) switching (HGAS)Phytoplankton dynamics at the North Atlantic Bloom Experiment(NABE) site for LGNS (left) and HGAS (right). (A) Average totalphyto concentration (0-55 m) compared to observations (circles).Averages (0-55 m) for all phyto types present of (B) growth (nutrientuptake minus sinking minus mortality), (C) growth minus grazing,and (D) total grazing pressure by both zoo types, (E) concentration.• 1 bloom peak instead of 2 observed (A) with 1 large (L2) and 1 small (S1) phyto type• types with highest growth (B) and winter biomass (E) dominate• grazing pressure between types differs only in magnitude (different, but constant preferences),increases simultaneously for all types (D)• thus growth minus grazing also decreases simultaneously (C)• 2 bloom peaks as in the observations (A), with high diversity (E)• growth minus grazing decreases at different times for phyto types of 1. and 2. peak (C)• types with high growth (B) and high winter biomass (E) dominate 1. peak• types with low growth (B) and lower grazing pressure than other types form 2. peak⇒ phytoplankton successionSimulations vs. Observations along the AMT• observations: highest diversity at mid latitudes• LGAS, HGAS: diversity pattern: maximum at mid lati-tudes, lower at low/high latitudes• LGNS, HGNS: diversity pattern less pronounced⇒ results with switching (LGAS, HGAS) fit the observedrange and latitudinal pattern better than with no switch-ing (LGNS, HGNS)Simulated annual average diversity (number of species) in the surfacelayer along the Atlantic Meridional Transect (AMT) compared to obser-vations (circles; Cermeño et al. 2008) for LGNS, HGNS, LGAS andHGAS.Summary & OutlookEffects of predation on phytoplankton diversity in ecosystem models:• predation increases diversity when a zooplankton community responseis included e.g. by active switching (zooplankton have variable,concentration-dependent selectivity for different phyto types)With switching:• simulated diversity agrees better with observed latitudinal diversity pattern•more realistic bloom dynamics at NABE• succession and coexistence of different phyto typesWhat’s next:assess the role of phytoplankton diversity for the functioning of the marineecosystem under environmental changeAdvanced school on Complexity, Adaptation and Emergence in Marine Ecosystems, 18–27 October 2010, Miramare - Triestefprowe@ifm-geomar.de

Top-down control of biodiversity

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