Trophic Structure & Food Webs 1946, Riley published a simple food web model: PP = 153T - 120P - 7.3N - 9.1Z + 6713 1947, simplified it to: dn/dt = N(Ph - R) - G
Trophic Structure & Food Webs 1946, Riley published a simple food web model: PP = 153T - 120P - 7.3N - 9.1Z + 6713 Phytoplankton Zooplankton 1947, simplified it to: dn/dt = N(Ph - R) - G Nutrients
Trophic Terminology! Top Down Control:! Regulation of ecosystems by predation! Bottom Up Control:! Regulation of ecosystems by physics! Trophic Cascades! Influencing any one box cascades to other boxes, not always linearly! The concept of r-k strategy! Food webs versus food chains
r versus K strategies Based on the concept of maximizing reproductive efficiency by balancing offspring versus parenting r < ---------------------------------------------------------------> K Rapid Growth Multiple offspring Short Life Small body size Invasive/Transient Generalists Slow growth Fewer offspring Long Life Large body size Established Specialist
Ramon Margalef (1978) updated the idea of r-k strategies for the ocean said that you can define species succession based on a phase space defined by energy (turbulence) and nutrients Margalef s s Mandala
Ecosystems and Energy Transfer! Ecosystem: : biotic community + environment! Producers! Consumers! Decomposers
Ecosystems and Energy Transfer! Energy is always lost!
With each transfer, some material (energy) goes to growth of the individual, some goes to respiration, some goes to waste products, some (can go) to reproduction.
Ecosystems and Energy Transfer! Trophic Levels: each level of organism! Trophic Transfer: percentage of energy
! Food Chains: short, direct transfer of energy from phytoplankton to apex predators
NPZ Models of Biology P Michaelis-Menten Respiration Temperature Light N Z Feeding efficiency Respiration, excretion Circulation/physics Remineralization time
Microbial Food Web! First recognized by Azam,, extended by others (Pomeroy, Wiebe, Hobbie)! 1977: Hobbie introduces Acridine Orange Direct Counts (AODC) 1980s-90s: Viruses discovered 2000: Archaea!
The Microbial Web! Viruses can account for a major source of phytoplankton mortality! Bacteria can provide 50% of phytoplankton nutrients! Some ecosystems can be net heterotrophic
Up to 20% of the biomass in the oceans may be associated with archaea. What are they doing?
Illustration by S. Cook, Scripps Institution of Oceanography
What is DOM? Operational definition: organic matter that passes a GF/F filter (nominal pore size of 0.7!m) DOM = Dissolved Organic Matter; DOC = Dissolved Organic Carbon; DON= Dissolved Organic Nitrogen; DOP=Dissolved Organic Phosphorous Includes 1. All (most) viruses 2. 50% of bacteria 3. Some phytoplankton (chlorophyll) 4. Many "submicron particles," e.g. colloids Items 1-3 generally not big part of DOM pool. Hansell, D.A. and C.A. Carlson (ed) 2002. Biogeochemistry of Marine Dissolved Organic Matter. Academic Press.
Deep water DOC is ca. 6000 years old. Same concentration of deep DOC is also in surface layer because oceans circulate on order of 1000 years Divide the DOC pool into three components: 1) Refractory DOM 2) Semi-labile DOM 3) Labile DOM
Bacterial Production and NPP are generally related Cole et al. (1988) Mar. Ecol. Progr. Ser 43: 1-10
Bacteria roughly follow phytoplankton Source of organic C 500 ) -1 d -2 400 300 Lakes & Estuaries Indian Bacterial Product 200 100 NA Rings N.PacificSubarctic Arctic Antarctica Equator N. Atlantic Arctic 0 200 400 600 800 1000 1200 1400 Primary Production (mg C m -2 d -1 )
So what is the microbial web?! About 50% of NPP goes through bacterial degradation (formation of DOM, respiration back to inorganic compounds)! For each size class of producer, there s s an equivalent consumer! In terms of new versus regenerated production, the microbial web is HOW the material is regenerated, and the microbial community is WHO is responsible
How do we measure it?! Who s s there! Flow Cytometry! Microscopy (with stains)! SEM/TEM (viruses)! Chemical analysis! What s s there! Chemical analysis! Radio-dating! NMR, mass spec, etc.! Rates (producers)! 3H-Thymidine! 3H-Leucine! Respiration! Rates (consumers)! Fluorescently Labeled Bacteria (FLB)! Grazer Dilution! Infection/Lysis
Who Cares? Air-Sea flux of: CO2, methane, DMS, oxygen, nitrogen gas Regeneration of nutrients Repackaging of organic matter Recycling and oxidation (rather than export)
Summary! In the 1970s, the importance of the microbial loop (web) was discovered! For each size class of producer, there is an equivalent consumer! Approximately 50% of NPP goes through this cycle (regenerated production)! Biogeochemistry is controlled by these processes! Boyd et al: in the absence of iron fertilization, HNLC regions are dominated by microzooplankton grazing