Transcript Ecosystems

Ecosystems
The Earth’s Spheres
1. The hydrosphere is the zone of water that covers over three-quarters
of the earth.
a. The ability of water to absorb and release great quantities of
heat keeps climate within livable range.
2. The atmosphere is the gaseous layer near earth.
a. The atmosphere is concentrated in lowest 10 kilometers;
extends thinly out to 1,000 km.
b. Major gases are nitrogen, oxygen and carbon dioxide.
3. The lithosphere is a rocky substratum that extends about 100
kilometers deep.
a. Weathering of rocks supplies minerals to plants and eventually
forms soil.
b. Soil contains decayed organic material (humus) that recycles
nutrients to plants.
4. The biosphere is the thin layer where life is possible between the
outer atmosphere and the lithosphere.
Ecosystems can range from a microcosm, such as an aquarium
– To a large area such as a lake or forest
Regardless of an ecosystem’s size
• Its dynamics involve two main processes: energy flow and
chemical cycling
– Energy flows through ecosystems
– While matter cycles within them
Factors affecting
Ecosystems
• Biotic: Living
• Abiotic: Nonliving
Clip
Energy flows through an ecosystem
–
Entering as light and exiting as heat
Tertiary
consumers
Microorganisms
and other
detritivores
Detritus
Secondary
consumers
Primary consumers
Primary producers
Heat
Key
Chemical cycling
Energy flow
Sun
Energy flows through an ecosystem
• First law of thermodynamics
– energy can neither be created nor destroyed; it
can only be changed from one form of energy to
another.
• Energy in an ecosystem is transformed by the
organism and passed through the food chains
• Second law of thermodynamics:
– when energy is transformed from one form to
another, there is always some loss of energy
from the system, usually as low grade heat.
Energy flows through an
ecosystem:
Food Chains and Webs
• A food chain
represents
passage of
energy through
populations in a
community.
– A trophic
level is a
feeding level of
one or more
populations in a
food web.
Quaternary
consumers
Carnivore
Tertiary
consumers
Carnivore
Carnivore
Carnivore
Herbivore
Secondary
consumers
Primary
consumers
Primary
producers
Animation
Carnivore
Plant
A terrestrial food chain
Carnivore
Zooplankton
Phytoplankton
A marine food chain
Energy flows through an
ecosystem:
Humans
Food Webs
• A food web
– Is a branching Baleen
food chain with whales
complex
Crab-eater seals
trophic
interactions
Birds
Smaller toothed
whales
Leopard
seals
Fishes
Sperm
whales
Elephant
seals
Squids
Carnivorous
plankton
Euphausids
(krill)
Copepods
Phytoplankton
Ecological Pyramids
• Shows the trophic
structure of an
ecosystem and the
energy content that
is passed to each
successive trophic
level in a food web.
All of the solar
energy that enters
an ecosystem is
eventually lost as
heat
Pyramid of energy
Ecological Efficiency
• When a caterpillar feeds on a plant leaf
• Only about one-sixth of the energy in the
leaf is used for secondary production
Plant material
eaten by caterpillar
200 J
Feces
100 J
67 J
33 J
Growth (new biomass)
Cellular
respiration
Ecological Efficiency
Ecological efficiency describes the efficiency with which energy
is transferred from one trophic level to the next
Ecological Pyramids and Efficiency
This rapid
loss of
energy is
the reason…
food
chains have
from three
to four
links, rarely
five.
there are
few large
carnivores.
Tertiary
consumers
Secondary
consumers
Primary
consumers
Primary
producers
10 J
100 J
1,000 J
10,000 J
1,000,000 J of sunlight
Primary productivity
• Rate at which autotrophs capture and store
energy within organic compounds over a
length of time.
Amount of light energy converted to chemical
energy (glucose)
• i.e.
•Net primary production (NPP)
•Is equal to GPP minus the energy used by the primary producers
for respiration
•Only NPP
•Is available to consumers
Measuring Primary Productivity
• Rate of O2 production
• Gross primary productivity is the
amount available to heterotrophs
• GPP is NPP + R
Since some of the O2 is used in respiration:
NPP= GPP - R
AP Lab #12
Dissolved Oxygen & Aquatic Primary Productivity
• You will…
– Measure primary productivity based on
changes in dissolved oxygen.
– Investigate the effects of changing light
intensity on primary productivity.
Biological
Magnification
– Ex: bald eagle 1950s -DDT
• DDT interferes with
the deposition of
calcium in eggshells
• DDT is now
outlawed
Concentration of PCBs
• Organisms at higher
trophic levels have
greater
concentrations of
accumulated toxins
stored in their
bodies.
PCBs: polychlorinated biphenyls
Herring
gull eggs
124 ppm
Lake
trout
4.83 ppm
Smelt
1.04 ppm
Zooplankton
0.123 ppm
Phytoplankton
Biogeochemical Cycles
• Life on Earth
– Depends on the recycling of essential
chemical elements
• Nutrient circuits that cycle matter through an ecosystem
– Involve both biotic and abiotic components and
are often called biogeochemical cycles
Hydrologic cycle
Carbon Cycle
Nitrogen cycle
Phosphorus cycle
Clip
• Gaseous forms of carbon, oxygen, sulfur,
and nitrogen
– Occur in the atmosphere and cycle globally
• Less mobile elements, including phosphorous,
potassium, and calcium
– Cycle on a more local level
1. In the hydrologic cycle,
freshwater evaporates and
condenses on the earth.
2. Evaporation of water from
the oceans leaves behind
salts.
3. Rainfall that permeates the
earth forms a water table at
the surface of the ground
water.
4. An aquifer is an underground
storage of fresh water in
porous rock trapped by
impervious rock
5. Freshwater makes up about 3
percent of the world's supply
of water and is a renewable
resource.
6. Freshwater becomes
unavailable when consumption
exceeds supply or is polluted
so it is not usable.
1. Terrestrial and aquatic
organisms exchange carbon
dioxide with the atmosphere.
2. Photosynthesis removes
CO2 from atmosphere;
respiration and combustion
add CO2 to atmosphere.
3. CO2 from the air combines
with water to produce
bicarbonate (HCO3), which
is a source of carbon for
aquatic producers, primarily
algae.
4. Similarly, when aquatic
organisms respire, the CO2
they release combines with
water to form HCO3.
5. The amount of HCO3 in the
water is in equilibrium with
the amount of CO2 in the air.
Animation
6. The reservoir for the carbon
cycle is largely composed of
organic matter, calcium carbonate
in shells, and limestone, as well
as fossil fuels.
Carbon Dioxide & Global
Warming
• CO2, nitrous oxide and methane
are gasses that contribute to
the rise in atmospheric
temperature
Global Warming (proposed)
Possible consequences of Global Warming
• Rising sea levels
• Increasing ocean
temperatures
• Severe weather
1. Nitrogen gas (N2) is 78% of
the atmosphere, yet nitrogen
deficiency often limits plant
growth.
2. In the nitrogen cycle, plants
cannot incorporate N2 into
organic compounds and
therefore depend on various
types of bacteria to make
nitrogen available to them.
3. Nitrogen Gas Becomes Fixed
a. Nitrogen fixation is the process
whereby N2 is reduced and
added to organic compounds.
b. Some cyanobacteria in water and
free-living bacteria in soil are
able to reduce N2 to ammonium
(NH4+).
c. Other nitrogen-fixing bacteria,
living in nodules on the roots of
legumes, make reduced nitrogen
and organic compounds available
to the host plant.
d. Plants cannot fix atmospheric
nitrogen but take up both NH4+
and nitrate (NO3-) from the
soil.
e. After plants take up NO3-, it is
enzymatically reduced to NH4+
used to synthesize amino and
nucleic acids.
Animation
4. Nitrogen Gas Becomes Nitrates
a. Nitrification is the production of
NO3-.
b. Nitrogen gas is converted to NO3in the atmosphere when cosmic
radiation, meteor trails, and
lightning provide the high energy
for nitrogen to react with oxygen.
c. Nitrifying bacteria convert NH4+ to
NO3-.
d. Ammonium in the soil is converted to
NO3- by nitrifying bacteria in the
soil in a two-step process:
1) First, nitrite-producing bacteria
convert NH4+ to nitrite (NO3-).
2) Then, nitrate-producing bacteria
convert NO2 - to NO3-.
e. Denitrification is conversion of
NO3- to nitrous oxide (N2O) and
N2.
f. There are denitrifying bacteria in
both aquatic and terrestrial
ecosystems.
g. Denitrification counterbalances
nitrogen fixation, but not
completely; more nitrogen fixation
occurs.
h. Humans contribute much to the
nitrogen cycle when they convert
N2 to ammonium and urea in
fertilizers.
i. Eutrophication (over enrichment)
results from fertilizer runoff;
when rampant algae dies off,
decomposers use up available
oxygen during cellular respiration,
and this results in a massive fish
•
5. Nitrogen and Air
Pollution
a. Production of
fertilizers and burning of fossil
fuels adds three times the
nitrogen oxides to the
atmosphere as
normal.
b. Acid deposition
occurs when nitrogen oxides
and sulfur oxides combine with
water vapor.
c. Photochemical
smog results when nitrogen
oxides and hydrocarbons react
in presence of sunlight;
smog contains ozone
and peroxyacetylnitrate (PAN)
and causes respiratory
problems.
d. Air pollutants are
trapped near the ground by
thermal inversions where cold
air is trapped near the
ground by warm air
above.
•
1. In phosphorus cycle,
weathering makes phosphate ions
(PO4 and HPO4 2-) available to plants
from the soil.
2. Some phosphate runs off into
aquatic ecosystems where algae
incorporate it into organic molecules.
3. Phosphate that is not taken up
by algae is incorporated into
sediments in the oceans.
4. Sediment phosphate only
becomes available when geological
upheaval exposes sedimentary rocks.
5. Phosphate taken up by
producers is incorporated into a variety
of organic compounds.
6. Animals eat producers and
incorporate some of phosphate into
long-lasting teeth, bones, and shells.
7. Decay of organisms and
decomposition of animal wastes
makes phosphate ions available again.
8. Available phosphate is
generally taken up quickly; it is usually
a limiting nutrient in most ecosystems.
Animation
Phosphorus and Water Pollution
1. Humans boost the supply of phosphate by mining
phosphate ores for fertilizers, detergents, etc.
2. Run-off of animal wastes from livestock feedlots
and commercial fertilizers from cropland as well as
discharge of untreated and treated municipal
sewage can all add excess phosphate to nearby waters.
3. Eutrophication is the name of this overenrichment and can lead to algal blooms; when the
algae die off, decomposers use up the oxygen
5. Oil spills add over 5 million metric tons of oil a
year to oceans.
6. Human activities including fishing have exploited
ocean resources to the brink of extinction.
Human Impact
•
•
•
•
•
•
•
•
Greenhouse effect
Ozone depletion
Acid Rain
Desertification
Deforestation
Pollution
Reduction in species diversity
Introduction of nonendemic species
Rising Atmospheric CO2
• Due to the increased burning of fossil fuels and
other human activities
390
1.05
380
0.90
0.75
370
Temperature
0.60
360
0.45
350
0.30
340
CO2
330
0
320
0.15
310
 0.30
300
1960 1965 1970 1975
Figure 54.24
0.15
Temperature variation (C)
CO2 concentration (ppm)
– The concentration of atmospheric CO2 has been
steadily increasing
 0.45
1980 1985 1990 1995 2000 2005
Year
• Modeling
ecosystems
- trophic
components