Ecosystems I Test II
224 billion tons per year
annual total production of dry plant biomass =
% of annual plant biomass produced in terrestrial ecosystems
% of terrestrial plant biomass used by humans as food/fiber crops or feed for animals
90%, 10%
According to Pauly and Christensen, about ___% of consumed energy is used to maintain the consumer, meaning that only ____% is converted through growth and reproduction to biomass, and thus potential food for other organisms.
Charles Elton’s contribution (English ecologist of the 1920’s)
Argued that organisms living in the same place not only had similar tolerances of physical factors in the environment but also interacted with one another, most importantly in a system of feeding relationstips that he called a food web.
A.G. Tansley’s contribution (English plant ecologist of the 1930’s)
First to consider animals and plants, together with the physical factors of their surroundings, as ecological systems. He called this concept the ecosystem and regarded it as the fundamental unit of ecological organization.
Alfred J. Lotka’s contribution (Chemist)
He developed the first thermodynamic concept of the ecosystem. He was the first to consider populations and communities as energy-transforming systems, and suggested that each system can be described in principle by a set of equations that represent exchanges of matter and energy among its components. (i.e. assimilation of CO2 into organic carbon compounds by plants, consumption of plants by herbivores, and consumption of animals by carnivores.
Lotka’s thermodynamic principles
energy transformations of ecosystems grow in direct proportion to their size, productivity, and inefficiency. earth itself is a giant thermodynamic machine in which the circulation of winds and ocean currents and the evaporation of water are driven by the energy in sunlight. part of that energy is assimilated by the photosynthesis of plants and this energy ultimately fuels all biological systems.
food chain
sequence of feeding relationships by which energy passes through the ecosystem
Raymond Lindeman’s contribution (young aquatic ecologist at U of M)
brought attention to the concept of the ecosystem as an energy-transforming system in 1942. coined terms “trophic level,” “pyramid of energy,” and argued that energy is lost at each level because of the work performed by organisms at that level and because of the inefficiency of biological energy transformations.
trophic level
greek “trophic” = food. link of the food chain, i.e. plant, herbivore, carnivore.
pyramid of energy
less energy reaches each successively higher trophic level.
ecosystem ecology’s conception
1950’s- cycling of matter and associated passage of energy through an ecosystem provides a basis for characterizing that system’s structure and function. can compare energy and elements in different ecosystems as common “currency.”
Eugene P. Odum’s contributions (University of Georgia)
text “Fundamentals of Ecology,” 1953, influenced a generation of ecologists. he depicted ecosystems as energy flow diagrams to convey the principle that energy passes from one trophic level to the next.
light, heat
energy enters ecosystems as _____ and leaves as _____.
primary production
when plants, algae, and some bacteria capture light energy and transform it into the energy of chemical bonds in carbohydrates.
photosynthesis equation
(6)CO2 + (6)H20 -> C6H12O6 + (6)O2
oxidized, reduced
photosynthesis transforms carbon from a(n) _________ (low-energy) state in CO2 to a _________ (high-energy) state in carbohydrates.
39 kilojoules (kJ)
for each gram of carbon assimilated, a plant transfers _________ kJ of energy from sunlight to the chemical energy of carbon in carbohydrates.
small, 1/3, heat
plant pigments that capture the energy of light for photosynthesis actually absorb a ______ fraction of the total incident solar radiation. plants assimilate about ______ of the light energy absorbed by those photosynthetic pigments. the rest is lost as _____.
rearranged and joined together, ____ molecules become fats, starches, oils, and cellulose.
proteins, nucleic acids, pigments
combined with nitrogen, phosphorus, sulfur, and magnesium, simple carbs derived from glucose produce an array of _______, ________ ______, and _______.
gross primary production
total energy assimilated by photosynthesis
net primary production
energy accumulated in plants and which is therefore available to consumers
energy of respiration
amount of energy used by plants for maintenance and biosynthesis. this is the difference between net and gross primary production (gross doesn’t subtract this)
the energy equivalent of an organic compound depends primarily on its ____ content
39 kJ
organic compounds contain approximately ___ kJ of metabolizable energy per gram of carbon
amount of plant biomass produced in a year
in terrestrial ecosystems, ecologists often estimate net production by measuring the amount of _______.
aboveground net productivity- most common basis for comparing terrestrial communities
assimilation, respiration
when a plant is exposed to light, carbon dioxide flux includes both ____ (uptake) and _____ (output), and thus measures net production.
for plants growing in full sunlight, light levels usually exceed the ______ pt. of their photosynthetic pigments and is therefore not restricted by light availability
photosynthetic efficiency
percentage of the energy in sunlight that is converted to net primary production during the growing season.
1-2%. what happens to the remaining 98-99%? leaves reflect some and molecules other than photosynthetic pigments absorb most of the remainder.
where water and nutrients do not limit plant production severely, the photosynthetic efficiency of an ecosystem as a whole varies between ___ and ___ %.
leaves and other surfaces reflect anywhere from ___ – ____% of light energy.
rate of photosynthesis ______ as temperature rises (up to a pt.)
16 degrees C, 38 degrees C
optimum temp. for photosynthesis varies with the prevailing temperature of the environment- from about ____degrees C in many temperate species to as high as _____ degrees C in tropical species.
increases, decrease
net production depends on the rate of respiration as well as on the rate of photosynthesis, and respiration generally ____ with increasing leaf temp. thus, net prod. (and therefore net assim. of CO2) may _______ with increased temp.
stomates, water, transpiration
tiny openings in leaves through which CO2 and O2 are exchanged with the atmosphere, and which also allow ___ to leave the leaf by ____.
when soil moisture approaches a plant’s wilting point, stomates _____.
transpiration efficiency (water use efficiency)
number of grams of dry matter produced (net production) per kilogram of water transpired
2g/kg, 4g/kg
in most plants, transpiration efficiencies are < ___ g of production per kilogram of water, but they may be as high as ____ g per kilogram in drought-tolerant crops
nitrogen, phosphorus
when nitrogen and phosphorus fertilizers were applied singly and in combination to chaparral habitat in southern Ca, most species responded with increased production to additions of _____ but not _____.
phosphorus, nitrogen
growth of Ca lilac bushes, which harbor nitrogen-fixing bacteria in their root systems, responded to the addition of _____ but not _____.
nutrients limit primary production most strongly in ___ environments.
only ___ – ___% of energy passes between trophic levels
ecological efficiency (food chain efficiency)
percentage of energy transferred from one trophic level to the next
regurgitation of food components that are difficult to digest.
assimilated energy
ingested energy – egested energy
assimilated energy – respiration – excretion
assimilation efficiency
ratio of assimilation to ingestion, usually expressed as a percentage. depends on food quality,
the most active animals have the ____ net production efficiencies
net production efficiency
ratio of energy contained in an organism’s production to the total assimilated energy
low, high
active, warm-blooded animals exhibit ____ net prod., sedentary, cold-blooded animals, particularly aquatic, have _____ net prod.
gross production efficiency
product of assimilation efficiency and net prod. efficiency
net production efficiency for plants
ratio of net production to gross production (plants)
dead remains of plants and undigestible excreta of herbivores
exploitation efficiency
proportion of prod. on one trophic level that is consumed by organisms on the next higher level.
residence time
the longer the ______ ____, the greater the accumulation of energy
residence time
(energy stored in biomass)/(net productivity)
biomass accumulation ratio
(biomass)/(rate of biomassproduction)
energy budget
lindeman constructed the first ____ ____, for cedar bog lake in mn.
organic materials produced outside the system
photosynthesis that occurs within the system
autochthonous, allochthonous
in general, _____ prod. predominates in large rivers, lakes, and most marine ecosystems; ______ prod. make up the largest part of energy flux in small streams and springs under the closed canopies of forests.
egested, detritus
material not assimilated is _____ and becomes part of the _____ food chain.
oxygen saturation
equilibrium amount of dissolved O2 pure water can hold
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