I. Concept 55.2: Energy and other limiting factors control primary production
in ecosystems
a. ___________________________ ___________________________ in an ecosystem is
the amount of light energy converted to chemical energy by
autotrophs during a given time period
b. The extent of photosynthetic production sets the spending limit for an
ecosystem’s energy budget
i. The amount of solar radiation reaching the Earth’s surface
___________________________ photosynthetic output of ecosystems
1. Only a small fraction (1%) of solar energy actually
strikes photosynthetic organisms, and is converted to
chemical energy.
c. Total primary production is known as the ecosystem’s
___________________________ primary production (_____________________ )
i. ___________________________ primary production (________________)
is GPP minus energy used by primary producers for respiration
1. Only NPP is available to ___________________________
2. Ecosystems vary greatly in NPP and contribution to the
total NPP on Earth
ii. ___________________________ crop is the total biomass of
photosynthetic ___________________________ at a given time
d. Tropical rain forests, estuaries, and coral reefs are among the most
productive ecosystems per unit area
e. Marine ecosystems are relatively ___________________________ per unit
area, but contribute much to global net primary production because of
their volume
f. In marine and freshwater ecosystems, both ___________________________
and ___________________________ control primary production
i. Depth of light penetration affects primary production in the
photic zone of an ocean or lake
ii. More than light, nutrients limit primary production in
geographic regions of the ocean and in lakes
g. A ___________________________ ___________________________ is the element
that must be added for production to increase in an area
i. ___________________________ and ___________________________ are
typically the nutrients that most often limit marine production
1. Nutrient enrichment experiments confirmed that
nitrogen was limiting phytoplankton growth off the
shore of Long Island, New York
ii. Experiments in the Sargasso Sea in the subtropical Atlantic
Ocean showed that iron limited primary production
iii. Upwelling of nutrient-rich waters in parts of the oceans
contributes to regions of high primary production
h. The addition of large amounts of nutrients to lakes has a wide range of
ecological impacts
i. In some areas, sewage runoff and fertilizer pollution has caused
j.
___________________________ of lakes, which can lead to loss of most fish
species
In terrestrial ecosystems, ___________________________ and
___________________________ affect primary production on a large scale
i. Actual ___________________________ is the water annually
transpired by plants and evaporated from a landscape
1. It is related to ___________________________ primary
production
2. On a more local scale, a soil nutrient is often the limiting
factor in primary production
Lecture Questions 55.1 Physical Laws Govern Ecosystems
1. Explain how the first and second laws of thermodynamics apply to ecosystems.
Lecture Questions 55.2 Primary Production in Ecosystems
1. Define and compare gross primary production and net primary production.
2. Define and compare net primary production and standing crop.
II. Concept 55.3: Energy transfer between trophic levels is typically only 10%
efficient
a. _______________________________ production of an ecosystem is the amount
of chemical energy in food converted to their own new biomass
during a given period of time
i. When a caterpillar feeds on a leaf, only about one-sixth of the
leaf’s energy is used for secondary production
b. An organism’s _______________________________ efficiency is the fraction of
energy stored in food that is not used for respiration
i. If we view animals as energy transformers, we can ask
questions about their relative efficiencies.
ii. Production efficiency = net secondary production/assimilation
of primary production.
1. Net secondary production is the energy stored in
biomass represented by _______________________________ and
_______________________________.
c. _______________________________ consists of the total energy taken in and
used for growth, reproduction and respiration.
i. In other words production efficiency is the fraction of food
energy that is not used for respiration.
1. This differs between organisms.
d. _______________________________ efficiency is the percentage of production
transferred from one trophic level to the next
i. It usually ranges from 5% to 20%
ii. Trophic efficiency is multiplied over the length of a food chain
iii. Approximately 0.1% of chemical energy fixed by
photosynthesis reaches a _______________________________ consumer
e. A pyramid of net production represents the loss of energy with each
transfer in a food chain
f. In a _______________________________ pyramid, each tier represents the dry
weight of all organisms in one trophic level
i. Most biomass pyramids show a sharp
_______________________________ at successively higher trophic
levels
1. Certain aquatic ecosystems have
_______________________________ biomass pyramids:
producers (phytoplankton) are consumed so quickly
that they are outweighed by primary consumers
g. _______________________________ _______________________________ is a ratio of the
standing crop biomass to production (p)
h. Dynamics of energy flow in ecosystems have important implications
for the human population
i. Eating meat is a relatively inefficient way of tapping
photosynthetic production
Lecture Questions 55.3 Secondary Production in Ecosystems
1. Explain what factors may limit primary production in aquatic ecosystems.
2. Distinguish between each of the following pairs of terms:
a. primary and secondary production
b. production efficiency and trophic efficiency
3. Explain why aquatic ecosystems may have inverted biomass pyramids.
III. Concept 55.4: Biological and geochemical processes cycle nutrients between
organic and inorganic parts of an ecosystem
a. Life depends on recycling chemical elements
b. Nutrient circuits in ecosystems involve biotic and abiotic components
and are often called _______________________________ cycles
c. In studying cycling of water, carbon, nitrogen, and phosphorus,
ecologists focus on four factors:
i. Each chemical’s biological importance
ii. Forms in which each chemical is available or used by
organisms
iii. Major reservoirs for each chemical
iv. Key processes driving movement of each chemical through its
cycle
d. The Water Cycle
i. Water is essential to all organisms
ii. 97% of the biosphere’s water is contained in the
_______________________________, 2% is in glaciers and polar ice caps,
and 1% is in lakes, rivers, and groundwater
iii. Water moves by the processes of evaporation,
_______________________________, condensation, precipitation, and
movement through surface and groundwater
e. The Carbon Cycle
i. Carbon-based organic molecules are essential to all organisms
ii. Carbon reservoirs include fossil fuels, soils and sediments,
solutes in oceans, plant and animal biomass, and the
atmosphere
iii. CO2 is taken up and released through photosynthesis and
respiration; additionally, _______________________________ and the
burning of fossil fuels contribute CO2 to the atmosphere
f. The Terrestrial Nitrogen Cycle
i. Nitrogen is a component of amino acids, proteins, and nucleic
acids
ii. The main reservoir of nitrogen is the
_______________________________ (N2), though this nitrogen must be
converted to NH4+ or NO3– for uptake by plants, via
_______________________________ _______________________________ by
bacteria
iii. Organic nitrogen is decomposed to NH4+ by ammonification,
and NH4+ is decomposed to NO3– by _______________________________
_______________________________ converts NO3– back to N2
g. The Phosphorus Cycle
i. Phosphorus is a major constituent of nucleic acids,
phospholipids, and ATP
1. _______________________________ (PO43–) is the most
important inorganic form of phosphorus
ii. The largest reservoirs are _______________________________ rocks of
marine origin, the oceans, and organisms
iii. Phosphate binds with soil particles, and movement is often
localized
h. Decomposition and Nutrient Cycling Rates
i. Decomposers (_______________________________) play a key role in
the general pattern of chemical cycling
ii. Rates at which nutrients cycle in different ecosystems vary
greatly, mostly as a result of differing rates of decomposition
1. The rate of decomposition is controlled by
_______________________________, moisture, and nutrient
availability
2. ______________________________ decomposition results in
relatively low levels of nutrients in the soil
Lecture Questions 55.4 The Cycling of Chemical Elements in Ecosystems
1. Name the main processes driving the water cycle.
2. Describe the four nutrient reservoirs and the processes that transfer the elements
between reservoirs.
3. Describe the nitrogen cycle and explain the importance of nitrogen fixation to all living
organisms. Name three other key bacterial processes in the nitrogen cycle.
IV. Concept 55.5: Human activities now dominate most chemical cycles on Earth
a. As the human population has grown, our activities have disrupted the
trophic structure, energy flow, and chemical cycling of many
ecosystems
i. In addition to transporting nutrients from one location to
another, humans have added new materials, some of them
toxins, to ecosystems
b. The quality of soil varies with the amount of organic material it
contains
i. Agriculture removes from ecosystems nutrients that would
ordinarily be cycled back into the soil
c. _______________________________ _______________________________ for a nutrient
is the amount that plants can absorb without damaging the ecosystem
i. When excess nutrients are added to an ecosystem, the critical
load is exceeded
1. Remaining nutrients can _______________________________
groundwater as well as freshwater and marine
ecosystems
d. Combustion of fossil fuels is the main cause of acid precipitation.
i. Releases oxides of sulfur and nitrogen that react with water in
the atmosphere to produce sulfuric and nitric acids.
ii. North American and European ecosystems downwind from
industrial regions have been damaged by rain and snow
containing nitric and sulfuric acid
iii. Acid precipitation changes soil pH and causes leaching of
calcium and other nutrients.
iv. Environmental regulations and new technologies have allowed
many developed countries to reduce sulfur dioxide emissions.
e. Humans release many toxic chemicals, including synthetics previously
unknown to nature. In some cases, harmful substances persist for long
periods in an ecosystem
i. One reason toxins are harmful is that they become more
_______________________________ in successive trophic levels
f. _______________________________ _______________________________ concentrates
toxins at higher trophic levels, where biomass is lower
i. PCBs and many pesticides such as DDT are subject to biological
magnification in ecosystems
ii. In the 1960s Rachel Carson brought attention to the
biomagnification of DDT in birds in her book Silent Spring
g. One pressing problem caused by human activities is the rising level of
atmospheric carbon dioxide
i. Due to the burning of fossil fuels and other human activities,
the concentration of atmospheric CO2 has been steadily
increasing
1. How Elevated CO2 Levels Affect Forest Ecology: The
FACTS-I Experiment
a. The FACTS-I experiment is testing how elevated
CO2 influences tree growth, carbon
concentration in soils, and other factors over a
ten-year period
b. The CO2-enriched plots produced more wood
than the control plots, though less than expected
c. The availability of nitrogen and other nutrients
appears to limit tree growth and uptake of CO2
h. CO2, water vapor, and other greenhouse gases reflect infrared
radiation back toward Earth; this is the greenhouse effect
i. This effect is important for keeping Earth’s surface at a
habitable temperature
i.
ii. Increased levels of atmospheric CO2 are magnifying the
greenhouse effect, which could cause global warming and
climatic change
iii. Increasing concentration of atmospheric CO2 is linked to
increasing global temperature
1. Northern coniferous forests and tundra show the
strongest effects of global warming
2. A warming trend would also affect the geographic
distribution of precipitation
Life on Earth is protected from damaging effects of UV radiation by a
protective layer of ozone molecules in the atmosphere
i. Satellite studies suggest that the ozone layer has been
gradually thinning since 1975
ii. Destruction of atmospheric ozone probably results from
chlorine-releasing pollutants such as CFCs produced by human
activity
iii. Ozone depletion causes DNA damage in plants and poorer
phytoplankton growth
iv. An international agreement signed in 1987 has resulted in a
decrease in ozone depletion
Lecture Questions 55.5 Human Impact on Ecosystems and the Biosphere
1. Explain why toxic compounds usually have the greatest effect on top-level carnivores.