Ecosystem Energy and Nutrient Flow

Ecosystems

• 1. Biotic community and the abiotic environment.

• 2. Functional system which transfers and circulates energy and matter.

Function, not Species -- Stuff, not Things

Ecosystem:

“a spatially explicit unit of the Earth that includes all of the organisms, along with all the components of the abiotic environment within its boundaries.”

Gene Likens

ECOSYSTEM ECOLOGY

ENERGY

Ecosystems Are Energy Transformers

• J.M. Teal (1962)

Trophic Structure Reminder

•Express trophic structure as energy transfer

•Energy pyramids can never be inverted

•Is there room for anyone else

at the top of this food chain?

21.1 Production• Energy flow in an ecosystem: primarily

plants – GPP: Gross Primary Production

• Energy fixed in photosynthesis

– NPP: Net Primary Production• Biomass accrued by plants: wt. living plant material• Energy loss: respiration, tissue turnover, herbivory

Characteristics of Top Carnivores

not dense (few per unit area) because of ecological efficiency

large territory (widely ranging)

large body

long life

fast moving

charismatic

hunt-able

Extirpation

Indirect Effects – Trophic Cascade

Transfer Efficiencies

Plants

A (GPP)=2000

Herbivores A=50

Carnivores A=8

P=10

Solar Energy=

1,000,000

AE=50%

R+E=1000

R=50

I1=100

I=10

R=2

NPP=1000

P=1

E=40

E=7

AE= %

AE=80%

Kcal m-2 y-1

Transfer Efficiencies

Plants

A (GPP)=2000

Herbivores A=50

Carnivores A=8

P=10

Solar Energy=

1,000,000

AE=50%

R+E=1000

R=50

I1=100

I=10

R=2

NPP=1000

P=1

E=40

E=7

AE= %

AE=80%

Kcal m-2 y-1

Transfer Efficiencies

Plants

A (GPP)=2000

Herbivores A=50

Carnivores A=8

P=10

Solar Energy=

1,000,000

AE=50%

R+E=1000

R=50

I1=100

I=10

R=2

NPP=1000

P=1

E=40

E=7

AE= %

AE=80%

Kcal m-2 y-1

Transfer Efficiencies

Plants

A (GPP)=2000

Herbivores A=50

Carnivores A=8

P=10

Solar Energy=

1,000,000

AE=50%

R+E=1000

R=50

I1=100

I=10

R=2

NPP=1000

P=1

E=40

E=7

AE= %

AE=80%

Kcal m-2 y-1

Transfer Efficiencies

Plants

A (GPP)=2000

Herbivores A=50

Carnivores A=8

P=10

Solar Energy=

1,000,000

AE=50%

R+E=1000

R=50

I1=100

I=10

R=2

NPP=1000

P=1

E=40

E=7

AE=2%

AE=80%

Kcal m-2 y-1

Transfer Efficiencies

Plants

A (GPP)=2000

Herbivores A=50

Carnivores A=8

P=10

Solar Energy=

1,000,000

AE= %

R+E=1000

R=50

I=100

I=10

R=2

NPP=1000

P=1

E=40

E=7

AE=2%

AE=80%

Kcal m-2 y-1

Transfer Efficiencies

Plants

A (GPP)=2000

Herbivores A=50

Carnivores A=8

P=10

Solar Energy=

1,000,000

AE=50%

R+E=1000

R=50

I1=100

I=10

R=2

NPP=1000

P=1

E=40

E=7

AE=2%

AE=80%

Kcal m-2 y-1

Transfer Efficiencies

Plants

A (GPP)=2000

Herbivores A=50

Carnivores A=8

P=10

Solar Energy=

1,000,000

AE=50%

R+E=1000

R=50

I=100

I=10

R=2

NPP=1000

P=1

E=40

E=7

AE=2%

AE=80%

Kcal m-2 y-1

Transfer Efficiencies

Plants

A (GPP)=2000

Herbivores A=50

Carnivores A=8

P=10

Solar Energy=

1,000,000

AE=50%

R+E=1000

R=50

I1=100

I=10

R=2

NPP=1000

P=1

E=40

E=7

AE=2%

AE= %

Kcal m-2 y-1

Transfer Efficiencies

Plants

A (GPP)=2000

Herbivores A=50

Carnivores A=8

P=10

Solar Energy=

1,000,000

AE=50%

R+E=1000

R=50

I1=100

I=10

R=2

NPP=1000

P=1

E=40

E=7

AE=2%

AE=80%

Kcal m-2 y-1

Transfer Efficiencies

Plants

A (GPP)=2000

Herbivores A=50

Carnivores A=8

P=10

Solar Energy=

1,000,000

AE=50%

R+E=1000

R=50

I1=100

I=10

R=2

NPP=1000

P=1

E=40

E=7

AE=2%

AE=80%

Kcal m-2 y-1

Transfer Efficiencies

Plants

A (GPP)=2000

Herbivores A=50

Carnivores A=8

P=10

Solar Energy=

1,000,000

AE=50%

R+E=1000

R=50

I1=100

I=10

R=2

NPP=1000

P=1

E=40

E=7

AE=2%

AE=80%

Kcal m-2 y-1

Take home: Ecosystems are Energy Transformers

• Approximate 10% energy transfer between each trophic level

• More efficient energy use as you increase trophic levels

• Is there room for anyone else at the top of the pyramid?

• Which level is most important to pyramid stability?

Ray Lindeman 1942

First

Ecosystem model

Eugene Odum 1953.

Silver Springs, Florida.

Carbon cycle

http://www.grida.no/climate/vital/13.htm, 1980-1989

Steady State (Equilibrium)

Trillions of moles (per year)

Turnover Time = 38,000,000/8400 = 4524 years

Turnover rate is about 0.022% per year

ECOLOGICAL STOICHIOMETRY

Elemental Ratios

REDFIELD RATIO C:N:P 106:16:1

C:N – decaying wood, DOC.N:P -- cyanobacteria advantage.

C:P – phosphate limitation for Daphnia.

ECOSYSTEM ECOLOGY

ENERGY FLOW

CHEMICAL CYCLES

Trophic Structure Principles

• Eltonian pyramids

• Number of individuals per species

• Is this pyramid stable?

Trophic Structure Principles

• What if we transformed each species into biomass instead of absolute numbers?

Trophic Structure Reminder

• Do biomass or counts include generation time/reproduction, how much energy is available for growth, or decomposers?

Measuring the Energy Content of Plants

• Calorimetry– Heat generation

• Harvesting– Linear growth– Clip plots: whymeasure dry weight?

• CO2 uptake method – Li-Cor photosynthesis system

• O2 output– Lt. and dk. bottles

• Chlorophyll concentration

ECOSYSTEM

SCALES

Ecosystem: (trophic-dynamic)

the system composed of physical-chemical-biological processes active within a space-time unit of any magnitude… Ray Lindeman 1941

Cedar Ck. Bog, MN

Lake Wingra – ECOSYSTEM BOUNDARIES

ECOSYSTEM

Compartments include leaves, wood, soil, rhizosphere.

Small size scale.

Compartments contain living & non-living

TROPHIC STRUCTURE

Defined by energy flow.

primary producer

primary consumer (herbivore)

secondary consumer (carnivore)

…,

top carnivore.

 

BOUNDARIES

Average Annual

Net Primary Productivity,

by Habitat

Ricklefs Fig. 6.8

Fig. 6.2 Ricklefs -- E.P Odum’s universal model of ecological energy flow

TROPHIC STRUCTURE

Defined by energy flow.

primary producer

primary consumer (herbivore)

secondary consumer (carnivore)

…,

top carnivore.

 

Measuring Primary Productivity

 Oxygen method

c14 method – a radioactive tracer technique 

annual production

CALORIMETRY

Measuring Energy Flow

calorie = 1 degree C increase at 15 degrees C, for 1 ml water

1000 calories = 1 Calorie

carbohydrate and protein about 5 Cal per gram

fat about 9 Cal per gram

teaspoon sugar = 4 grams or 20 Calories (kilocalories)

TROPHIC CONCEPTS

Productivity

Biomass

Turnover Time = Pool/Input = Biomass/Productivity

Turnover Rate = Inverse of Turnover Time

At equilibrium, Input = Output

ECOLOGICAL EFFICIENCY

Ratio of the productivity for two adjacent trophic levels.

EXAMPLE

primary productivity = 2 grams per m2 per day

herbivore productivity = 0.2 grams per m2 per day,

then the ecological efficiency is: ???

Rule of Thumb

The ecological efficiency is ~ 10% per trophic level.

TROPHIC CASCADES (CARPENTER)

DIRECT & INDIRECT EFFECTS

OF

TOP PREDATORS

ON

BIOMASS

PRODUCTIVITY

Bottom-Up; Top-Down effects

Microbial Loop

Extra links

reduce amount of energy reaching predators by about 90%.

Nitrogen Excretion:

Ammonium, Urea, Uric Acid

Atmospheric Carbon & Global Warming

MASS BALANCE: Application of conservation of matter;

Input & Output:

Pool (Reservoir)

Equilibrium

Steady State

Source & Sink

Flux

Net

Turnover Rate & Time

Burial

Ricklefs Fig. 7.5 – Global Carbon Cycle

ECOSYSTEM MANIPULATIONS & THE NITROGEN CYCLE

Bormann and Likens (1970) -- HUBBARD BROOK, NH

ecological consequences of clear-cutting a 38‑acre watershed in a New Hampshire Experimental Forest

Organic N oxidized to nitrate, producing nitric acid

pH of stream decreased

nitrogen fixation decreased

nutrients rapidly flushed out of the watershed

[P04]: surrogate for primary productivity

PHOTOSYNTHESIS

RESPIRATION

Gross Primary Productivity

Respiration

Net Primary Productivity

NPP = GPP - R