ECOSYSTEM ECOLOGY

Ecosystem:

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

(Abiotic factors: energy, water, carbon, nitrogen, phosphorous)

• All the biotic and abiotic factors in a community.

Fig. 55-4

Microorganismsand other

detritivores

Tertiary consumers

Secondaryconsumers

Primary consumers

Primary producers

Detritus

Heat

SunChemical cycling

Key

Energy flow

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 flowsthrough communities...

Ecosystem Energy Budgets:

Primary Productivity (PP)

Secondary Productivity (SP1, SP2…)

• Photosynthesis powers primary productivity.

Primary Productivity (PP)

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

• Rate at which energy or biomass is produced per unit area by plants (primary producers)

Which of these ecosystems accounts for the largest amount of Earth’s primary productivity?

A) Tundra

B) Savannah

C) Salt marsh

D) Open ocean

E) Tropical rainforest

Figure 56.5

Figure 56.5

Distribution of Primary Terrestrial Production Worldwide

Positive Correlation Between Productivity and Sunlight

Positive Correlation Between Productivity and...

Precipitation Temperature

Net

pri

mar

y p

rodu

ctio

n (g

/m2 ·

yr)

Fig. 55-8

Tropical forest

Actual evapotranspiration (mm H2O/yr)

Temperate forest

Mountain coniferous forest

Temperate grassland

Arctic tundra

Desertshrubland

1,5001,00050000

1,000

2,000

3,000·

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

Primaryproducers

100 J

1,000,000 J of sunlight

10 J

1,000 J

10,000 J

Primaryconsumers

Secondaryconsumers

Tertiaryconsumers

Where does all the energy go???

Fig. 55-9

Cellularrespiration100 J

Growth (new biomass)

Feces

200 J

33 J

67 J

Plant materialeaten by caterpillar

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 toSP1 to SP2...

1) consumption efficiency

2) assimilation efficiency

3) production efficiency

1) consumption efficiency (CE)

% of total productivity at one trophic levelthat 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 availablefor growth, reproduction

(remainder lost as feces)

AE is higher in carnivores (~80%) than in herbivores (20-50%). WHY?

A) Carnivores chew their food more.B) Herbivores chew their food more.C) Plant tissues are not as easy to digest

as meat.D) Meat is not as easy to digest as plant

tissues.

Elephant dung

3) production efficiency (PE)

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

(remainder lost as respiratory heat)

PE of endotherms (<10%) is lower than PE of ectotherms (30-40%). WHY?

A) Because endotherms have feathers and fur.

B) Because endotherms move more quickly than ectotherms.

C) Because ectotherms move more quickly than endotherms.

D) Because ectotherms get energy from the sun.

• SP1 is the % of PP that is incorporated at the next highest trophic level…

• SP2 is the % of SP1 that is incorporated at thenext highest trophic level…

This is NEVER 100%.

And that is why big fierceanimals are rare!

• Energy loss at each trophic level limits thelength of a food chain...

Atmosphere

Lithosphere Hydrosphere

Living Organisms

+Detritus

Biogeochemical Cycles

• 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

• Water is essential to all organisms

• 97% in the oceans

• 2% in glaciers and polar ice caps

• 1% in lakes, rivers, and groundwater

The Water Cycle

• Evaporation, transpiration, condensation, precipitation, and movement through surface and groundwater

• Carbon-based organic molecules are essential to all organisms

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

The Carbon Cycle

• CO2 taken up via photosynthesis and released via respiration

• Volcanoes and burning of fossil fuels contribute CO2 to atmosphere (2.9 B metric tons/yr)

CO2

CO

2 con

cen

trat

ion

(p

pm

)

Temperature

1960300

Ave

rage

glo

bal

tem

per

atu

re (

ºC)

1965 1970 1975 1980Year

1985 1990 1995 2000 200513.6

13.7

13.8

13.9

14.0

14.1

14.2

14.3

14.4

14.5

14.6

14.7

14.8

14.9

310

320

330

340

350

360

370

380

390 Greenhouse Gases and Global Warming

Global Temperature Changes

• Nitrogen is a component of amino acids, proteins, and nucleic acids

• Main reservoir of nitrogen is in atmosphere (N2)

• N2 converted to NH3 via nitrogen-fixing bacteria

The Nitrogen Cycle

• NH3 decomposed to NH4+, which can be decomposed to NO3

– by nitrifying bacteria; both 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.

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

• Nitrogen 14 from atmosphere• Nitrogen 15 from salmon