Ecosystems
1. Population Interactions
2. Energy Flow
3. Material Cycle
• The deep sea was once thought to
have few forms of life because of the
darkness (no photosynthesis) and
tremendous pressures.
• But in 1977, a whole new kind of
community was discovered in the
deep sea.
• The invertebrates supply the bacteria
with CO2, O2, and sulfides at higher
rates than they could get if they were
free-living.
• The symbiosis is therefore a mutualism
and results in higher productivity than if
the organisms lived separately.
• Chemoautotrophic bacteria arrive first,
sometimes in very high densities.
• Tube worms are often the first
invertebrates to arrive.
• Clams and other mollusks are better
competitors and over time they increase
in abundance at the expense of the
tube worms.
Succession in Hydrothermal Vent Communities
Ecosystem Energetics
• Sunlight is the most significant source of
energy
• Solar energy (photons)
– Used by photoautotrophs
– Drives weather, water cycle, and causes the
currents of air and water
Ecosystem Energetics
• Energy flows through the ecosystem
• The flow of energy is subjected to physical
laws
The Laws of Thermodynamics
• Energy exists in two forms
– Potential energy - stored energy
– Kinetic energy - energy in motion
– Work is the storage of energy and the
arranging or ordering of matter
The Laws of Thermodynamics
Govern Energy Flow
• Two laws of thermodynamics govern the
expenditure and storage of energy
– The first law of thermodynamics
– The second law of thermodynamics
The Laws of Thermodynamics
Govern Energy Flow
• The first law of thermodynamics: energy
is neither created nor destroyed
– Exothermic - energy released
– Endothermic- energy absorbed
One-way flow of energy
Heat
+
1 C6H12O6
energy rich
6 CO2 + 6 H2O
energy poor
The Laws of Thermodynamics
The second law of thermodynamics: energy is
is always lost during transfer
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”
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
What causes there to be less biomass at higher levels?
Fig. 54.12a
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Pyramids of energy
Fig. 54.11
What causes there to be a loss of energy at each tropic level?
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Energy Flow
• Primary Productivity
• Gross primary productivity
• Net primary productivity
Concept 20.1
Primary Production
• Primary production is the chemical
energy generated by autotrophs during
photosynthesis and chemosynthesis.
• It is the source of energy for all
organisms, from bacteria to humans.
Concept 20.1
Primary Production
• Autotrophs store energy as carbon
compounds
• Carbon is the currency used to
measure primary production.
• Primary productivity is the rate of
primary production.
Concept 20.1
Primary Production
• Gross primary production (GPP)—
total amount of carbon fixed by
autotrophs.
• GPP depends on photosynthetic rate.
• Photosynthetic rate is influenced by
climate and leaf area index (LAI)—leaf
area per unit of ground area.
Concept 20.1
Primary Production
• LAI varies among biomes:
• Less than 0.1 in Arctic tundra (less than
10% of the ground surface has leaf
cover).
• 12 in boreal and tropical forests (12
layers of leaves between the canopy
and the ground, on average).
Concept 20.1
Primary Production
• Because of shading, the incremental
gain in photosynthesis for each added
leaf layer decreases.
Concept 20.1
Primary Production
• Plants use about half of the carbon
fixed in photosynthesis for cellular
respiration.
• Plants with a lot of nonphotosynthetic
tissue (e.g., trees) have higher
respiratory carbon losses.
• Respiration rate increases with
temperature, so tropical forests have
higher respiratory losses.
Concept 20.1
Primary Production
• Net primary production
• (NPP) = GPP –Respiration
• NPP results in an increase in biomass
(living plant matter).
• NPP is the energy left over for plant
growth and for consumption by
detritivores and herbivores.
Concept 20.1
Primary Production
• Plants can respond to environmental
conditions by allocating carbon to the
growth of different tissues.
• Example: Grassland and desert plants
allocate more NPP to roots because
soil nutrients and water are scarce.
Allocation of NPP to Roots
Concept 20.1
Primary Production
• Allocation of NPP to storage products
(e.g., starch) provides insurance
against loss of tissue to herbivores,
disturbances such as fire, and climatic
events such as frost.
• Substantial amounts of NPP (up to
20%) may be allocated to defensive
secondary compounds.
Concept 20.1
Primary Production
• NPP varies during succession, as LAI
(ratio of photosynthetic to
nonphotosynthetic tissue) and species
composition all change.
• Highest NPP is usually during
intermediate stages when plant
diversity and nutrient supply tend to be
highest.
The Trajectory of Succession
Highest diversity and
NPP
Concept 20.1
Primary Production
• In old-growth forests, NPP may decline
as LAI and photosynthetic rates
decrease.
• Old-growth ecosystems have large
pools of stored carbon and nutrients
and provide habitat for many animal
species.
• The decrease in NPP over time is far
less pronounced in grasslands than in
forests.
Temperature, Water, and Nutrients Control Primary
Production in Terrestrial Ecosystems
• Temperature and precipitation influence
one another and thus have interacting
effects on primary productivity
– Warm air temperatures increase the potential
for evaporation and increase transpiration
rates and water demand
– If temperatures are low, rates of
photosynthesis and productivity will be low
regardless of water availability
Temperature, Water, and Nutrients Control Primary
Production in Terrestrial Ecosystems
• Warm temperatures and an adequate water
supply for transpiration give the highest
primary productivity
– Actual evapotranspiration (AET) is the
combined value of surface evaporation and
transpiration
Temperature, Water, and Nutrients Control Primary
Production in Terrestrial Ecosystems
• NPP increases with increasing nutrient
availability
• Nitrogen availability drives patterns of
forest primary productivity
– Increasing primary productivity with available
nitrogen
Temperature, Water, and Nutrients Control Primary
Production in Terrestrial Ecosystems
• NPP increases with increasing nutrient
availability
Temperature, Water, and Nutrients Control
Primary Production in Terrestrial
Ecosystems
• Global productivity patterns reflect the
influence of climate in terrestrial
ecosystems and the global patterns of
temperature and precipitation
Temperature, Water, and Nutrients Control Primary
Production in Terrestrial Ecosystems
• The regions of highest NPP are located in
the equatorial zone
– Year-round warm temperatures and ample
precipitation
Concept 20.1
Primary Production
• It is important to be able to measure
NPP:
– NPP is the ultimate source of energy for all
organisms in an ecosystem.
– Variation in NPP is an indication of
ecosystem health.
– NPP is associated with the global carbon
cycle.
Concept 20.1
Primary Production
• Terrestrial ecosystems:
• NPP is estimated by measuring
increase in plant biomass in
experimental plots and scaling up to the
whole ecosystem.
Concept 20.1
Primary Production
• Harvest techniques:
• Measure biomass before and after
growing season.
• This is a reasonable estimate of
aboveground NPP if corrections are
made for herbivory and mortality.
Concept 20.1
Primary Production
• Harvest techniques are impractical for
large or biologically diverse
ecosystems.
• Chlorophyll concentrations can be a
proxy for GPP and NPP:
•
Estimate using remote sensing
methods that rely on reflection of solar
radiation.
Spectral Signatures of Vegetation Clear Water,
and Bare Soil
Primary Production
• NDVI (normalized difference vegetation
index):
( NIR  red )
NDVI 
( NIR  red )
• NIR = Near-infrared wavelengths (700–1000
nm)
• red = red wavelengths (600–700 nm)
Concept 20.1
Primary Production
• Vegetation has a high NDVI value;
water and soil have low NDVI values.
NDVI over large
spatial scales is
measured using
satellite sensors.
Concept 20.1
Primary Production
• NDVI and remote sensing can be used
to estimate CO2 uptake and NPP,
deforestation, desertification,
atmospheric pollution, and other
phenomena.
Remote Sensing of Terrestrial NPP
Concept 20.1
Primary Production
• Phytoplankton do most of the
photosynthesis in aquatic habitats.
• Phytoplankton have short life spans, so
biomass at any given time is low
compared with NPP; harvest
techniques are not used.
Concept 20.1
Primary Production
• Remote sensing of chlorophyll
concentrations in the ocean using
satellites provides good estimates of
marine NPP.
• Indices are developed to indicate how
much light is being absorbed by
chlorophyll, which is then related to
NPP.
Remote Sensing of Marine NPP