Ecosystem =

Ecosystem =

A group of interacting populations and their

physical environment.

All interacting by a flow of energy and

with their physical and chemical

environments.

Ecosystems can be

Small

Large

Ecosystems

1. Population Interactions

2. Energy Flow

3. Material Cycles

Ecosystems

1. Population Interactions

2. Energy Flow

3. Material Cycles

Modes of Nutrition

• Autotrophs

– Capture sunlight or chemical energy

– Primary producers

• Heterotrophs

– Extract energy from other organisms or

organic wastes

– Consumers, decomposers, detritivores

Simple

Ecosystem

Model

Energy

input from

sun

Nutrient

Cycling

Producers

Autotrophs (plants and other

self-feeding organisms)

Consumers

Heterotrophs (animals, most fungi,

many protists, many bacteria)

Energy output (mainly metabolic heat)

Role of Organisms

• Producers

(photoautotrophs)

Primary Producers

Photoautotrophs

+ + + C6H12O6

+ O2

sugar oxygen Sunlight + water + CO2 + minerals =

=

Energy Materials

Role of Organisms

• Consumers

1. Herbivore

2. Carnivores

3. Omnivores

4. Parasites

5. Decomposers

Role of Organisms • Consumers

1. Herbivore

2. Carnivores

3. Omnivores

4. Parasites

5. Decomposers

Role of Organisms • Consumers

1. Herbivore

2. Carnivores

3. Omnivores

4. Parasites

5. Decomposers

Role of Organisms • Consumers

1. Herbivore

2. Carnivores

3. Omnivores

4. Parasites

5. Decomposers

Role of Organisms • Consumers

1. Herbivore

2. Carnivores

3. Omnivores

4. Parasites

5. Decomposers

Trophic Levels

• Feeding relationships

– All organisms at a trophic level are the same

number of steps away from the energy input

into the system

• Autotrophs are producers

– closest to energy input

– first trophic level

4th trophic level

3rd trophic level

2nd trophic level

1st trophic level

Food Chain

Food Chain

• A straight-line

sequence of who

eats whom

• Simple food

chains are rare in

nature

marsh hawk

upland sandpiper

garter snake

cutworm

plants

Food Web

Biological Magnification

Non-degradable or slowly degradable

substances become more and more

concentrated in tissues of organisms at

higher trophic levels of a food web

DDT in Food Webs

• Synthetic pesticide banned

in United States since

1970s

• Carnivorous birds

accumulate DDT in their

tissues, produce brittle egg

shells

Ecosystems

1. Population Interactions

2. Energy Flow

3. Material Cycle

Energy Flow

• Primary Productivity

• Gross primary productivity

• Net primary productivity

Primary Productivity

• Gross primary productivity is

ecosystem’s total rate of photosynthesis

• Net primary productivity is rate at which

producers store energy in tissues in

excess of their aerobic respiration

Ecological Pyramids

• Primary producers are bases for

successive tiers of consumers

• Biomass pyramid

– Dry weight of all organisms

• Energy pyramid

– Usable energy decreases as it is

transferred through ecosystem

Pyramids of biomass

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 54.12a

What causes there to be less biomass at higher levels?

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 54.11

Pyramids of energy

What causes there to be a loss of energy at each tropic level?

Thermodynamics

• First Law – energy is neither created

nor destroyed when converted

from one form to another

• Second Law – whenever

there is a change of energy

from one form to another,

some is lost in the form of

heat and thus cannot

perform work

One-way flow of energy

+

1 C6H12O6 6 CO2 + 6 H2O

Heat

energy rich energy poor

2nd Law Cont.

Entropy – a measure of disorder in a system

• disorder spontaneously increases over time

• Matter has a tendency to reach a higher state

of entropy and lower state of potential energy

“The Rule of Ten” or “10% Law”

Ecosystem Structure

1. Population Interactions

2. Energy Flow

3. Material Cycle (Biogeochemical Cycle) • Hydrologic cycle

– Water

• Atmospheric cycles

– Nitrogen and carbon

• Sedimentary cycles

– Phosphorus and other nutrients

Water Cycle

atmosphere

ocean land

evaporation

from ocean

425,000

precipitation

into ocean

385,000

evaporation from land

plants (evapotranspiration)

71,000

precipitation

onto land

111,000

wind-driven water vapor

40,000

surface and

groundwater

flow 40,000

Aquifer

Plants Influence the Water Cycle

Plants Protect Soil

Hubbard Brook Experiment

• A watershed was experimentally

stripped of vegetation

• All surface water draining from

watershed was measured

• Deforestation caused increase in

nutrient content of runoff water

The Effect of Deforestation on nutrient erosion

Wetlands

Groundwater Pollution

Dust Bowl – 1930s

Dust storm approaching Stratford, Texas

Groundwater Depletion

Galveston

Carbon Cycle

Reservoir:

Carbon - Biomass Holding Stations

Decomposition

Rates

Higher rates in forests

due to favorable

conditions

(moist and warm)

Not much carbon

accumulates

Peat Bog Slow decomposition

due to anaerobic

conditions, more C

accumulates

Peat Moss Bog man

Source to Atmosphere

Carbon Cycle

Greenhouse Effect

Galveston

4°C = 0.6m sea level

Comparison of the Muir Glacier, SE

Alaska, in 1941 and 2004

Muir Glacier, SE Alaska

August, 1941 August, 2004

photo: William Field photo: Bruce Molnia

Arctic Ice Cap

• water 200m below

the arctic icecap –

1996 was 1°C

warmer than in 1991

1990-present – decades of

record-breaking disasters

Carbon dioxide (CO2)

Carbon dioxide (CO2) – 50% Chlorofluorocarbons (CFCs) – 25%

Methane (CH4) – 15% Nitrous oxide (N2O) – 10%

80’s Hair Do’s

Nitrogen Cycle

• Reservoir – atmosphere

Nitrogen Fixation

• Source to Plants –

Nitrogen-fixing bacteria

• Source to Plants –

Cyanobacteria Bacteria in

Root Nodules of Legumes

Decomposition

• Source to Plants –

Plant Limiting Factor for Growth

Nitrogen Cycle – Atmospheric N-fixing bacteria

ammonium

Nitrogen (N2) (NH4)

Nitrogen Cycle –

Organic Material Ammonifying bacteria ammonium (NH4)

Nitrogen Cycle –

NH4+ Nitrifying Bacteria NO3

-

Nitrogen Cycle –

NO3- Denitrifying Bacteria N2

Nitrogen Cycle

nitrate (NO3-) Plant Uptake

ammonium (NH4+)

Nitrogen Cycle

Oligotrophic waters of coral reefs

The mystery of coral reefs

•Reefs support an

impressive diversity

and abundance of

life

•Where do the

nutrients come

from?

Cyanobacteria fix nitrogen for the

community

• Algal growth in and on the coral is dominated

by nitrogen fixing cyanobacteria

• Flow over the reef and light levels determine N

fixation rate

• How do

we know?

Leave ceramic plates for turf algae

to grow on

Nitrogen fixation measurement • Generate acetylene (H-CΞC-H) by

dropping calcium carbide (Ca-CΞC-Ca)

into water and collect gas that bubbles up

• Then inject gas into air above water

(head space) in

“doughnut” flume

Nitrogen fixation measurement

• “doughnut” flume

• Cyanobacteria “reduce” acetylene to ethylene (H2-C=C-H2)

• They can’t tell it’s not N2

• We measure amount of ethylene produced over time as proxy for N2 fixation

We can compare N fixation over

time and at different light levels

3 Sept Exp 1

All Data Points

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 50 100 150 200 250 300 350

Elapsed Time (min)

Eth

yle

ne c

on

c.

(nm

ol)

NFix vs Light

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0 200 400 600 800 1000 1200

PAR (micromol photons)

slo

pe

31-Aug

1-Sep

2-Sep

3-Sep