OUR Ecological Footprint - 111.

11

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 2009

IB 440: Plants and Global Change

spring 2009

Energy flow in ecosystemsObjectives:

The ecosystem obeys thermodynamic principles.• Trophic pyramids for energy, biomass, numbers• Primary production: efficiencies and factors causing variation among biomes• Secondary production:• Intertrophic transfers: efficiencies and food chain length Intratrophic transfers: efficiencies

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”

‘Universal’ model of energy flow through ecosystems.

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

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

Heat is lost as energy flows through food chain. Matter recycles…

Blue = matterRed = 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 1

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

Indirect measures of GPP

Figure 2

*** Measurements of PP by IRGA

Full sun: CO2 depleted from chamber at rate of 12 mg CO2 per 100 cm2 leaf area per hourDark: CO2 released by leaf into chamber at rate of 1.5 mg CO2 per 100 cm2 leaf area per hour

What is the rate of NPP for this leaf? Explain.What is the rate of respiration for this leaf? Explain.What is the rate of GPP for this leaf? Explain.

Figure 3

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?

• Light• Temperature• Precipitation• Nutrients• CO2

Photosynthesis and light…PS efficiency = % sun’s energy into NPP

Figure 4

NPP vs. Temperature and Precipitation

Figure 5

Water use efficiency = G NPP per kg water transpired

NPP vs. nitrogen (N in rubisco in PS)

Figure 6

Nutrient use efficiency =g production per g N assimilated

Nutrient use efficiency varies among biomes

Figure 7

Productivity and nutrients

Figure 8

NPP + > [CO2]

• To what extent is PS limited by

amount of CO2?

• To what extent does vegetation

act as a C sink?

Hypothesis: Sp richness and functional diversity increase NPP (via more biomass).

Figure 9

Results

Figure 10

Remote sensing of primary production in oceans.

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 11

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.

Figure 12

What is the conclusion? Figure 12

Global variation in estimated NPP

Figure 13

NPP varies among habitats:

Figure 14

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

Food chains represent energy relationships.

Producers (autotrophs)

Consumers(heterotrophs)

Figure 15

90% lost at each level

100

10

1

.1

Energy Pyramid: 10% law of energy transfer; 2nd law limits number of levels.

Figure 16

Energy transfer between trophic levelsdepends on:

• NPP

• efficiencies of transfer between trophic levels

• residence time

longer time--> > accumulation of energy

Food energy available to the human population depends on their trophic level.

Figure 17

***Pyramids: Which can be inverted? Why?Energy

Biomass

Numbers

Figure 18

sun1

20

15

10

Ecological (food chain) efficiency =net production of trophic level_n net production of trophic level n-1

Figure 19

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%)

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?

Figure 20

What limits the length of the food chain?

Figure 21

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.

***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 7.1Coastal marine 8000 10.0 20 5.1Grassland 2000 1.0 10 4.3Tropical forest 8000 10.0 5 3.2

Figure 22

Secondary production

• By non-photosynthesizers

• Amount of chemical energy in consumer’s food converted to biomass /unit time

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

Figure 23

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