Ecosystem Ecology: Energy Flow & Nutrient Cycling

ECOSYSTEM ECOLOGY

Ecosystem: • The organisms in a particular area and the physical environment with which they interact.

• All the biotic and abiotic factors in a community. (Abiotic factors: energy, water, carbon, nitrogen, phosphorous)

Fig. 55-4

Tertiary consumers Microorganisms and other detritivores

Detritus

Secondary consumers

Primary consumers

Primary producers Heat Key Chemical cycling Energy flow

Sun

Energy Flow through Ecosystems • Energy flows through ecosystems as organisms capture and store energy, then transfer it to organisms that eat them. • These organisms are grouped into trophic levels...

Trophic Levels:

Route of energy flow

- food chain

- food web - pyramid of numbers

Pyramid of Numbers

Question: “Why are big fierce animals rare?” Charles Elton, 1927

Answer: Because of the way energy flows through communities...

Ecosystem Energy Budgets: Primary Productivity (PP) Secondary Productivity (SP1, SP2)

Primary Productivity (PP) • Rate at which energy or biomass is produced

per unit area by plants (primary producers) • Photosynthesis powers primary productivity.

• The annual productivity of an area is determined primarily by sunlight, temperature, and moisture.

Distribution of Primary Production Worldwide

Figure 56.5

Figure 56.5

Positive Correlation Between Productivity and Sunlight

Positive Correlation Between Productivity and...

Precipitation

Temperature

Fig. 55-8

Net primary production (g/m2·yr) ·

3,000

Tropical forest

2,000

Temperate forest

1,000

Mountain coniferous forest Desert shrubland

0

Temperate grassland

Arctic tundra 0

500 1,500 1,000 Actual evapotranspiration (mm H2O/yr)

Secondary Productivity (SP1, SP2…) • rate of production of new biomass from PP by heterotrophic organisms (primary and secondary consumers)

• positively correlated with rainfall...

Fig. 55-10

Tertiary consumers Secondary consumers

10 J

100 J

Primary consumers

1,000 J

Primary producers

10,000 J

1,000,000 J of sunlight

Where does all the energy go???

Fig. 55-9

Plant material eaten by caterpillar

200 J

67 J Feces

100 J

33 J Growth (new biomass)

Cellular respiration

Ecological Efficiency: Percent of energy transferred from one trophic level to the next.

Three categories of transfer efficiency are required to predict energy flow from PP to SP1 to SP2... 1) consumption efficiency 2) assimilation efficiency

3) production efficiency

1) consumption efficiency (CE) % of total productivity at one trophic level that is consumed by the next highest level

(remainder not eaten)

Green World Hypothesis

• Plants have many defenses against herbivores

2) assimilation efficiency (AE) % of ingested food energy that is assimilated (i.e. digested), and thus potentially available for growth, reproduction

(remainder lost as feces)

Elephant dung

3) production efficiency (PE)

% of assimilated energy that is incorporated into new biomass (growth, reproduction)

(remainder lost as respiratory heat)

Implications?

• SP1 is the % of PP that is incorporated at the next highest trophic level. (Ditto for SP2…)

This is NEVER 100%. • Thus, energy loss at each trophic level limits the length of a food chain...

And that is why big fierce animals are rare!

Biogeochemical Cycles Nutrients exist in pools of chemical elements

FOUR main reservoirs where these nutrients exist are: 1) Atmosphere - carbon in carbon dioxide, nitrogen in atmospheric nitrogen 2) Lithosphere - the rocks - phosphates, calcium in calcium carbonate, potassium in feldspar

3) Hydrosphere - the water of oceans, lakes, streams and soil - nitrogen in dissolved nitrate, carbon in carbonic acid

Atmosphere

Living Organisms + Detritus Lithosphere

Hydrosphere

4) Living Organisms and Nutrient Cycles • Living organisms are a reservoir in which carbon exists in carbohydrates (mainly cellulose) and fats, nitrogen in protein, and phosphorus in ATP

• In studying cycling of water, carbon, nitrogen, and other chemicals, ecologists focus on four factors: – Biological importance of each chemical – Major reservoirs for each chemical – Forms in which each chemical is available or used by organisms – Key processes driving movement of each chemical through its cycle

The Water Cycle • Water is essential to all organisms

• 97% of the biosphere’s water is contained in the oceans, 2% is in glaciers and polar ice caps, and 1% is in lakes, rivers, and groundwater • Water moves by the processes of evaporation, transpiration, condensation, precipitation, and movement through surface and groundwater

The Carbon Cycle • Carbon-based organic molecules are essential to all organisms

• Carbon reservoirs include fossil fuels, soils and sediments, solutes in oceans, plant and animal biomass, and the atmosphere

• CO2 is taken up via photosynthesis and released via respiration • Volcanoes and the burning of fossil fuels contribute CO2 to the atmosphere

Fig. 55-21

14.9 390

14.8

380

14.7 14.6

370

Temperature

14.5

360

14.4 14.3

350

14.2

340

14.1

CO2 330

14.0

13.9

320

13.8 310 300

13.7 13.6 1960

1965

1970

1975

1980 1985 Year

1990

1995

2000

2005

… and Global Temperature

The Nitrogen Cycle • Nitrogen is a component of amino acids, proteins, and nucleic acids • The main reservoir of nitrogen is the atmosphere (N2)

• N2 is converted to NH3 via nitrogen-fixing bacteria • Organic nitrogen is decomposed to NH4+ by ammonification, and NH4+ is decomposed to NO3– by nitrifying bacteria; NH4+ and NO3– assimilated by plants

• Denitrifying bacteria convert NO3– back to N2

How Bears Feed Salmon to the Forest

• The run of salmon leads to a major flow of nutrients into estuaries and coastal watersheds

• Bears catch salmon in river and consume them in forest; on average, half the carcass is not eaten.

• Bears’ fat tissue is virtually nitrogen-free, so most of nitrogen in salmon protein is excreted as urine and feces.

• Nitrogen 14 from atmosphere • Nitrogen 15 from salmon

• Measurements of nitrogen isotope ratios in tree rings shows that nitrogen from salmon is incorporated into trees and enhances their growth