Biology 213 Chapter 55
Ecosystems and the Biosphere
You will be able to…
• Compare & contrast food chains, webs, and
pyramids
• Explain Bioaccumulation & magnification
• Describe C cycle, N cycle, P cycle & H2O
cycle in the biotic and abiotic environment.
• Examine human influence on natural cycles
• Describe role of the sun in
– Creating seasons
– Weather systems
– Developing ocean currents
– Creating a climate and weather
• Energy flow through an ecosystem
– Linear
– Sun to producer to consumer to decomposer
Is the sun the only
source of energy for
food webs?
Energy flow through an ecosystem
A food chain
Food chains, webs, & trophic levels.
Food chains, webs, & trophic levels.
Trophic relationships important in endangered
wildlife management:
e.g. DDT  Bald Eagle & Condors
• Ecological pyramids
Express progressive reduction in #’s of:
– Organisms
– Biomass
– energy
found in
successive
trophic levels
Food chains, webs, & trophic levels.
Not all animals or plants are eaten.
Portions (beaks, shells, bones, etc.)
not digested.
Matter & energy transfer not efficient.
Pyramids of biomass
Usually amount of fixed energy in an ecosystem is
measured in quantity of living material = biomass
Generally amount of biomass decreases at
successively higher trophic levels. Why?
Pyramid of biomass:
If you want to support a lot of humans,
what should you feed them?
Pyramids of energy
What happens to
the energy?
• Undigested parts
• Entropy
• Energy
expended in
“hunting” &
processing food
Bioaccumulation: build up of toxins in an organism
Biological magnification: increasing concentration
in successive trophic levels
• Gross primary productivity (GPP)
– Rate at which photosynthesis captures
energy
• Net primary productivity (NPP)
– Energy remaining after plants and other
producers carry out cellular respiration
What do you think are
the most productive ecosystems?
NPP for selected ecosystems
Ecosystem
Avg NPP (g dry matter/m2/yr)
Algal beds & reefs
Tropical rain forest
Swamp & marsh
Estuaries
Temperate evergreen forest
Temperate deciduous forest
Savanna
Boreal (northern) forest
2,500
2,200
2,000
1,500
1,300
1,200
900
800
NPP for selected ecosystems
Ecosystem
Avg NPP (g dry matter/m2/yr)
Woodland & shrubland
Agricultural land
Temperate grassland
Upwelling in oceans
Lake and stream
Arctic and alpine tundra
Open ocean
Desert and semi-desert scrubland
Extreme desert (rock, sand, ice)
700
650
600
500
250
140
125
90
3
Why is Carbon important in the ecosystem?
• What form is carbon used by plants?
– CO2 absorbed / O2 released
– Sugars (starch) formed
– Sugar used for Energy (cellular respiration)
• What form is carbon used by animals?
– Sugar used for Energy (cellular respiration)
– CO2 released / O2 absorbed
(see Joseph Priestly’s experiments)
Remember:
– C forms the “skeleton” for every biomolecule
How does Carbon cycle in the
environment?
Biotic factors:
• plants and animals: gaseous form
• Trees store carbon
• Seashells: solid form calcium carbonate
Abiotic factors:
• Atmospheric gas: circulates globally
• Mineral compounds: limestone
• Fossil fuels – remnants of ancient plants
and marine critters
Biogeochemical Cycles:
The Carbon cycle
–Carbon dioxide is the most important
gas (0.038% of air)
• gas phase allows for global
circulation
–Carbon enters plants as CO2
Biogeochemical Cycles:
The Carbon cycle
–CO2 returned to the environment:
• Cellular respiration
• Combustion & volcanoes
• Erosion of limestone
• Decomposition
Carbon cycle
Carbon Reservoirs: in billions of metric tons:
Atmosphere: 720
Ocean: 39,000
Carbonates: 100,000,000
Fossil fuels: 4,000
Soils: 1500
Land plants: 560
• most C is in rocks (carbonates & sediments)
• most C not in rocks is dissolved in ocean
• ~ 3 x more C in soils than in land plants
• Methane hydrates under sea floor
Carbon Cycle
Nitrogen cycle
Why is nitrogen
important to living
things?
How is it used?
Proteins,
DNA,
Chlorophyll
formation.
• Nitrogen cycle
– Five steps:
1. Nitrogen fixation
2. Nitrification
3. Assimilation
4. Ammonification
5. Denitrification
Nitrogen fixation:
2 moles of ammonia produced by prokaryotes
from 1 mole of N2 gas
N2 + 8H+ + 8e- + 16 ATP = 2NH3 + H2 + 16ADP + 16 Pi
Combustion, volcanoes, industry,
and lightning can fix N2 as nitrates & nitrites
Lightning: N2 + O2 --------------> 2 NO (nitric oxide)
Nitric oxide free radical combines with O2 to form NO2.
2 NO + O2 ---------------> 2NO2
Nitrogen dioxide dissolves in water to produce
nitric and nitrous acids;
2 NO2 + H2O -------> HNO3 + HNO2
These acids readily release NO3 & NO2 ions utilized by plants & micro-organisms.
HNO3 --------> H+ + NO3- (nitrate ions)
HNO2 --------> H+ + NO2- (nitrite ions)
Nitrification
Ammonia converted to ammonium to nitrate
Assimilation
• Roots absorb:
– Ammonia (NH3)
– Ammonium ions
– Nitrate ions
• Make plant proteins,
nucleic acids, &
chlorophyll
Ammonification
• Nitrogen compounds
released as wastes:
– Urea in urine
– Uric acid in bird
poop
• Compounds are
decomposed into
ammonia by bacteria
Denitrification
• Nitrate ions reduced to gaseous nitrogen by
denitrifying bacteria
• Reverse nitrogen fixing process
• Anaerobic environments: deep soil, swamps,
deep ocean
Nitrogen cycle
Both Carbon & Nitrogen cycles involve
gas, biological, & geochemical
reservoirs
• Phosphorus cycle
–Phosphorus erodes from rock as
inorganic phosphate
–Animals obtain it from their diet
–Plants obtain it from the soil
–Does not have a gaseous phase,
so cycles more locally
Phosphorus cycle: no gas phase
N and P are the major
limiting factors for plant growth
Guano happens!
• Sea bird deposits
• Bat caves
• Used extensively in
agriculture as a
fertilizer
• Used in detergents
• Run-off enters
streams
Eutrophication: enhanced phytoplankton
growth due excess supply of nutrients
• High concentrations of nutrients as run-off
from
– Sewage
– Agriculture
– Lawns
Eutrophication: enhanced phytoplankton
growth due excess supply of nutrients
• Phytoplankton “bloom”
• Phytoplankton die and are eaten by bacteria
• Oxygen levels depleted & fish die
Dr. David Schindler is an ecologist who
worked at the Experimental Lakes Project in
northern Ontario
– performed several
experiments on
eutrophication that led
to ban on phosphates
in detergents
Phosphates are the culprit
• Hydrologic cycle
– Renews supply of water
– Involves exchange of water btwn land,
ocean, atmosphere, and organisms
– Water enters atmosphere by evaporation
and transpiration
– Water leaves atmosphere as precipitation
– “Distillation” purifies water
Water Basins: Lakes, Oceans, Ice
How much fresh water is
there?
Transpiration and Evaporation
• Solar energy drives
evaporation
• Evaporation: ocean
surface is main
reservoir
• Transpiration: plants
release over 95% of
water they absorb
back into air
Condensation and precipitation
• Solar E drives surface
winds
• Winds carry moist air inland
and up over mountains
• Cooling air loses moisture
as condensation
• Precipitation: rain, sleet,
snow, hail, & fog
Storage:
percolation and ground water
• Aquifers may
take hundreds of
years to replenish
• Underground
aquifers
supply water for
– Streams
– Agriculture
– Wells
Ogallala Aquifer:
~95 % used for irrigation.
High Plains = 65 % of total
irrigated acreage in USA.
Overuse:
175,000 wells, irrigating
> 15 million acres.
Depleted much faster than
natural rate of recharge.
Some states 40 x higher.
Hydrologic cycle
Bottom-up processes
Availability of resources e.g. nutrient minerals
controls # of producers,
which controls # of herbivores,
which controls # of predators, etc.
Top-down processes:
Increase in top predators cascades down food web
Sunlight: primary source of energy
• Combo of Earth’s spherical shape
& axis tilt concentrate solar E at equator.
• Inclination of Earth’s axis primarily determines
the seasons
Amount of solar radiation reaching Earth
• 30% reflected back
• 47% absorbed by
atmosphere
• 23% runs
hydrologic cycle
• 1% drives wind and
ocean currents
• 0.02% captured
by photosynthesis
• 0.0001% used by
Culhane for
tanning
Seasonal changes in temperature
• Visible light & IR radiation warm surface
and lower part of atmosphere
• Atmospheric heat produces air movement,
which moderates the climate
Hadley cells
Global wind map
• Coriolis effect
– Tendency of moving air or water to be deflected
• Right in the Northern Hemisphere
• Left in the Southern Hemisphere
Does your toilet
really flush
straight down
on the equator?
Atmospheric circulation
Trade winds
Doldrums
Oceanic currents
• Generated by uneven
heating of ocean
surfaces
• Salinity differences
• Surface winds
Major surface ocean currents
Modifies temperatures and affects precipitation patterns
• Regional precipitation differences
– Influenced by latitude, elevation, topography,
vegetation, distance from large bodies of water,
and location
– Precipitation greatest where warm air passes over
ocean & then cools
Small D in sea surface temp D trade winds, which
D sea temp, which continues until atmospheric
circulation patterns & precipitation are disrupted across
Pacific & Indian Oceans, & surrounding continents
Look at the geography of major deserts
Why are they found in these locations?
Rain shadow
Sierra Nevadas
• California side
– Moist and lush
• Nevada side
– Dry and desertlike plant
communities
Much of the sun’s heat is trapped in
the atmosphere by CO2
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How has man influenced global climate?
Increased CO2 from burning fossil fuels
What are fossil fuels?
CO2 reservoir depleted: deforestation
Surface algae polluted
What will happen globally? Very complex!
What are the alternatives?