The hierarchical nature and processes of different levels of ecological systems:

Individual organism: How do structure, physiology, and behavior lead to the individual’s survival and reproduction? Population: What determines the number of individuals and their variation in time and space? Community: What determines the diversity and relative abundance of organisms living together? Ecosystem: How does energy flow and matter cycle in the biotic and abiotic environment? Biosphere: How do air, water, and the energy and chemicals they contain circulate globally?

Ecosystem Ecology: Interactions between abiotic and biotic factors at a given location as relates to: energy flow and cycling of matter. IB 452: Ecosystem Ecology fall 2011 IB 440: Plants and Global Change spring 2011

Energy flow in ecosystem Objectives: Ecosystem obeys thermodynamic principles. Trophic pyramid for energy Primary production: efficiencies and factors causing variation among biomes Secondary production: Intertrophic transfers: efficiencies and food chain length Intratrophic transfers: efficiencies Net ecosystem production: C gain - C loss

Food energy available to the human population depends on their trophic level. C54.14 Eating meat is inefficient way of tapping PS productivity. Humans obtain far more calories by eating grains directly as a primary consumer than by prcessing that same amount of grain through another trophic level. We could feed many more people if we all consumed only plant material, feeding more efficiently as primary consumers 224 billion tons of plant production/year 59% = terrestrial 35-40% used by humans directly (as plants) or indirectly (by feed animals first) Food supplies can be increased and more people can be supported by eating lower on food chain Figure 1 5

Ecosystem: an energy-transforming machine Exchanges of matter and energy among components Obey thermodynamic principles that govern energy transformations Law 1: Conservation of energy “balance the books” Law 2: Inefficient transformation of energy “heat tax” Law 1: energy neither created nor destroyed: have to ‘balance the books’

‘Universal’ model of energy flow through ecosystems.

Coupling of oxidations and reductions = basis of energy flow in ecosystems.

Energy flows through biochemical pathways Energy flows through biochemical pathways. Energy transfer decreases after each transformation.

Heat is lost as energy flows through food chain. Matter recycles… Blue = matter Red = energy What do red and blue arrows =? Blue = matter; red = energy

Primary Production: by plants process of converting light energy to chemical bond energy in carbohydrates (via photosynthesis!) for each g of C assimilated, 39 KJ energy stored rate determines rate of energy supply to rest of ecosystem

GrossPP = NetPP + Respiration Day + night Day Figure 2

IRGA - Infrared gas analzyer: measure CO2 in vs IRGA - Infrared gas analzyer: measure CO2 in vs. out: in sunlight (NPP) and dark (respiration); estimate GPP B15.14

Indirect measures of GPP Figure 3

How measure assimilation and respiration of CO2 over large spatial scales? Use eddy flux covariance towers Sensors quantify vertical movement of CO2 in atmosphere above vegetation. How temp and precip control primary proudction affect respiration of plants Helps to predict how ecosystem productivity migh change in response to climate change.

Abiotic Limits on Productivity Photosynthetic efficiency (% energy from sun converted to NPP) = 1-2% Net production efficiency (NPP/GPP) 30% tropics 75-80% temperate ***why difference? Variables affecting productivity: Light Temperature Precipitation Nutrients CO2

Photosynthesis and light… Figure 4

NPP vs. Temperature and Precipitation Effects of Temperature Optimum varies from 16 to 38 Rate of PS increases with T, but so does respiration Net assimilation may decrease at high temperatures Effects of Water PS on land is water-limited Water-use efficiency: 2 g production per kg of water transpired Water use efficiency = G NPP per kg water transpired Figure 5

NPP vs. nitrogen (N in rubisco in PS) Nutrients stimulate primary production N = most common limiting element; then P on land Aquatic systems often nutrient-limited Nutrient use efficiency = g production per g N assimilated Figure 6

NPP + > [CO2] To what extent is PS limited by amount of CO2? To what extent does vegetation act as a C sink?

Remote sensing of primary production in oceans. Spectral instrument estimates chlorophyll conc and converts data to contrasting artificial colors.

1° productivity of aquatic ecosystems depends on [nutrients]. Freshwater lakes: P often limiting; with low N/P, blue-green algae increase NPP because they can fix additional N; with high N/P, green algal ‘blooms’ occur Open ocean: near shore: N often limiting open ocean: silica and Fe more limiting

PP in aquatic ecosystems - highest where nutrients regenerated in sediments reach light zone. Figure 7

Question: Is NPP in the open ocean limited by nutrients (e.g Fe)? Hypothesis: NPP in the open ocean is limited by availability of iron. Experimental setup? Prediction: Amount of chlorophyll a increases both at surface and 30 m deep in area with added Fe relative to area without Fe.

Southern Ocean Iron Enrichment Experiment Southern Office Iron Enrichment Experiment (SO FEX) in areas of high and low silicon concentrations 25

Results: satellite images White = cloud False-color satellite images of each experimental area showing greatly increased phytoplankotn proudciton (as indiciate by chlorophylll a reflectance. 27

What is the conclusion? Figure 8 Fe fertilization increases ocean as C sink…but it also stimulates zooplankton production which releases CO2 to atmosphere and counters C sink argument. The So FE exp were more promising as much C precipitated below water mixing zone What is the conclusion? Figure 8

Global variation in estimated NPP Figure 9

NPP varies among habitats: 30

Energy flow between trophic levels

Energy flows through: Food chain – energy passes through many steps or links Trophic level (feeding level) = each link in food chain Two parallel food chains Plant-based Decomposer-based 32

Food chains represent energy relationships. Consumers (heterotrophs) Ecosystem trophic structure model: Spatial pattern set by autotrophs Decomposers blur the pattern Predators link components, stabilize system Producers (autotrophs) 33

Energy Pyramid: 10% law of energy transfer; 2nd law limits number of levels. 90% lost at each level .1 1 10 100 Figure 10

Energy transfer between trophic levels depends on: NPP efficiencies of transfer between trophic levels residence time longer time--> > accumulation of energy Monitor energy fluxes by considering various efficiencies and residence times of energy and results from food chain processing of energy by animals. Residence time varies: short in aquatic zooplankton; long in land Longer residence time - greater time to accumulate energy (biomass)

Ecological (food chain) efficiency = net production of trophic level_n net production of trophic level n-1 10 15 20 1 sun Figure 11

Ecological (food chain ) efficiency  Production of each trophic level = 5 – 20% that of level below it Replaces the “10% law”= an average; not fixed Often lower on land (5-15%) than aquatic (15-20%)

What limits the length of the food chain?

What limits length of food chain? H1: Energetics Availability of energy limits to 5-7 levels Depends on: NPP energy needed by consumers average ecological efficiency H2: Dynamic stability Longer chains less stable because: Fluctuations at lower trophic levels magnified at higher levels ---> extinction of top predators. Microcosms - useful for such tests…replicate essential features of ecosystem. Control all variables except ones of interest Get pix of 1.20

Do aquatic or terrestrial ecosystems have more trophic levels ***Do aquatic or terrestrial ecosystems have more trophic levels? What factor contributes most to variation in food chain length among these ecosystems? Community NPP Consumer Ecological # Trophic Ingestion Efficiency% Levels Open ocean 500 0.1 25 7.1 Coastal marine 8000 10.0 20 5.1 Grassland 2000 1.0 10 4.3 Tropical forest 8000 10.0 5 3.2 Figure 12

Secondary production By non-photosynthesizers Amount of chemical energy in consumer’s food converted to biomass /unit time Secondary production

Energy flow within a trophic level Secondary production = assimilated energy – respiration – excretion Figure 13

Some general rules Assimilation efficiency increases at higher trophic levels. Net and gross production efficiencies decrease at higher trophic level. Ecological efficiency averages about 10%. About 1% of NPP ends up as production on third trophic level; The pyramid of energy narrows quickly.

Net Ecosystem Production (NEP) = carbon gain - carbon lost Measures net carbon accumulation --> carbon ‘sequestered’ in organic cmpds in soil and living biomass --> no ‘greenhouse’ warming effect Positive NEP represents carbon sink --> removes CO2 from atmosphere

Exam ? Energy (kcal m-2 yr-1) Energy production Primary Primary Secondary __or removal_____ Producers Consumers Consumers Non-consumed production 704 70 13 Removed by consumers 176 34 0 Respiration 234 44 18 Gross production (totals) 1114____ 148 ____ 31____ 1) Calculate NPP. _____ 2) Calculate Ecological Efficiency during 2 transfers (= food chain efficiency). ______ ______ 3) What ultimately happens to 1) the energy and 2) the biomass that is not consumed in this lake? N.B. NPP - non-consumer+ consumed Ecological Efficiency = net 2ndP/net P so 104/880=11.8% and 13/104=12.5%