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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