BIOL 4120: Principles of Ecology Lecture 18: Ecosystem Ecology (Energy in the Ecosystem)

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BIOL 4120 Principles of Ecology Lecture 18
Ecosystem Ecology (Energy in the Ecosystem)

• Dafeng Hui
• Office Harned Hall 320
• Phone [phone]
• Email dhui_at_tnstate.edu

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Ecosystem

• Definition biotic community and abiotic
  environment functioning as a system. Includes
  organism-complex and whole complex of physical
  factors.
• Forest Ecosystem
• Forest is a system composed of autotrophy,
  heterotrophy, and abiotic environment, each
  component processing and exchanging energy and
  matter.
• Inputs exchanges from the surrounding
  environment into the ecosystem
• Outputs exchange from inside ecosystem to the
  surrounding environment
• Closed ecosystem an ecosystem with no inputs and
  outputs
• Open ecosystem an ecosystem with inputs and
  outputs
• Ecosystem ecology exchanges of energy and matter
  between ecosystem and environment and among
  components within the ecosystem (energy flow and
  nutrient cycling).

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Outline (Chapter 22)
18.1 Ecosystem function obeys thermodynamic
principles 18.2 Primary production provides
energy to the ecosystem 18.3 Many factors
influence primary production 18.4 Primary
production varies among ecosystems 18.5 Only 5
20 of assimilated energy passes between trophic
levels 18.6 Energy moves through ecosystems at
different rates 18.7 Ecosystem energetics
summarizes the movement of energy populations
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18.1 Ecosystem function obeys thermodynamic
principles
History of Ecosystem Ecology Alfred J. Lotka,
1925 Energy transformation and thermodynamic
principles Raymond Lindeman, 1942 Pyramid of
energy (left) Eugene Odum, University of
Georgia, 1953 Fundamentals of Ecology
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E. P. Odum developed a universal model of
energy flow through ecosystems. The energy
ingested by organisms at each trophic level is
reduced by respiration and excretion, so that
less energy is available for consumption by the
next trophic level.
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Laws of thermodynamics govern energy flow
First law of thermodynamics Energy is neither
created nor destroyed. Second law of
thermodynamics When energy is transferred or
transformed, part of the energy assumes a form
that cannot pass on any further. As energy is
transferred from one organism to another in the
form of food, a portion is stored as energy in
living tissue, whereas a large part of that
energy is dissipated as heat.
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18.2 Primary production provides energy to the
ecosystem
Flow of energy through a terrestrial ecosystem
starts with the harnessing of sunlight by
autotrophs. Rate at which light energy is
converted by photosynthesis to organic components
is referred to as primary productivity. Gross
primary productivity (GPP) Total rate of
photosynthesis Net primary productivity (NPP)
rate of energy as storage as organic matter after
respiration
NPPGPP-R
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• Productivity is the rate at which organic matter
  is created by photosynthesis (g m-2 yr-1)
• Standing crop biomass amount of accumulated
  organic matter in an area at a given time
• Biomass is expressed as g organic matter per
  square meter (g m-2)

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How to measure?

• Terrestrial ecosystem
• 1. Flux based
• Measure photosynthesis (equipment LiCor, Eddy
  flux method)
• net photosynthesis
• 2. Biomass based estimation
• Change in standing crop biomass (SCB) over a
  given time interval
• NPPdelta SCB loss of biomass due to death of
  plant loss due to consumption. (see Hui
  Jackson 2006 for grasslands)

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18.4 Primary production varies among ecosystems
Patterns of productivity reflect global patterns
of temperature and precipitation. High NPP in
equatorial zone and coastal region.
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Geographic variation in primary productivity of
worlds oceans

1. Great transport of nutrient from bottom to top
2. Nutrient from terrestrial ecosystems

High productivity is along coastal regions
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Recap Energy in ecosystems
1st and 2nd law of thermodynamics Primary
production provides energy to the ecosystem
Many factors influence primary
production Primary production varies among
ecosystems
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18.5 Only 5 20 of assimilated energy passes
between trophic levels

• Net primary production is the energy available to
  the heterotrophic component of the ecosystem
• Either herbivores or decomposers eventually
  consume all plant productivity, but often it is
  not all used within the same ecosystem.
• Secondary production net energy of production of
  consumers
• Energy stored in plant material, once consumed,
  some passes through the body as waste products.
• Of the energy assimilated, part is used as heat
  for metabolism (respiration) and maintenance
  capturing or harvesting food etc, and lost as
  heat.
• Energy left over from maintenance and respiration
  goes into production, including growth of new
  tissues and production of young
• Secondary productivity secondary production per
  unit of time

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Energy use is a complex process. Not all
consumers have the same efficiency A simple
model of energy flow through consumer I food
ingested by a consumer A a portion is
assimilated across the gut wall, convert nutrient
to body biomass (digestion, absorption) E
remainder is expelled from the body as waste
products (egested energy). animal excrete
small portion as nitrogen-containing
compounds (as ammonia, urea, uric acid)
(excreted energy) R of the energy assimilated,
part is used for respiration (respired
energy) P remainder goes to production (new
growth and reproduction)
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Based on these data, we can calculate Assimilatio
n efficiency A/I, ratio of
assimilation to ingestion measure the efficiency
with which consumer extracts energy from food
Secondary consumers 60-90 Production
efficiency P/A, ratio of
production to assimilation measure the
efficiency with which the consumer incorporates
assimilated energy into secondary production.
Homoeothermic low, 1 (birds) -6 (small
mammals) Poikilotherimic high, as much
as 75.
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Production efficiency varies mainly according to
taxonomic class Endotherms have low
P/A Invertebrates have high P/A Vertebrates
ectotherms have intermediate
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Energy flow through trophic levels can be
quantified
Energy flow within a single trophic compartment
Consumption efficiency In/Pn-1 Ecological
efficiency (food chain efficiency) Pn-1/Pn
14/2007
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18.6 Ecosystems have two major food chains
Food chain is a flow of energy Feeding
relationships within a food chain are defined in
terms of trophic or consumer level 1st level
Autotrophs or primary producer 2nd level
herbivores (1st level consumers) Higher level
carnivores (2nd level consumers) Some consumers
occupy more than one trophic level omnivores.
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Within any ecosystem, there are two major food
chains Difference 1. Source of energy for
herbivores 2. Energy flow direction 3.
interconnected
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18.7 Energy decreases in each successive trophic
level
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Energy pyramid
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M. Imhoff and L. Bounoua (NASAs Goddard Space
Flight Center) used satellite-derived data to
estimate the human appropriation of terrestrial
NPP (HANPP) Mean annual HANPP 24.2 Pg (1 Pg
1015 g) 20 percent of terrestrial annual
NPP HANPPWestern Europe/south central Asia 70
percent HANPPSouth America 6 percent
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18.8 Energy move through different ecosystems at
different rates
Ecological efficiency determine how much energy
assimilated by plants reach high level of tropic
levels. Another feature of energy transfer is
the rate of energy transfer (how fast or how long
energy stays in one tropic level) Residence
time (years) energy
stored in biomass (g m-2)
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-- net
productivity (g m-2 yr-1) Also called biomass
accumulation ratio Tropic 42 kg m-2/ 1.8 kg
m-2 yr-1 23 yrs
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Residence time for litter pools
Residence time (years)
litter accumulation (g m-2)
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-- rate of
litter fall (g m-2 yr-1) Forests Tropic 1-2
yrs Temperate (southeastern US) 4-16
yrs Mountain and boreal forests more than 100
yrs
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Net Ecosystem Productivity
NEP a measure of net carbon accumulation NEP
NPP Soil heterotrophic respiration GPP
Plant Respiration Soil heterotrophic
respiration GPP Aboveground Plant
Respiration Soil Respiration NEP 1 2 of
the total gross primary production (2 billion
tons) Fossil fuel burning 8 billion tons of
carbon
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The End
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Relationship of Secondary production and primary
production
Secondary production depends on primary
production for energy Sam McNaughton (Syracuse
Uni.) 69 studies for terrestrial ecosystems
(from Arctic tundra to tropical forests)
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Similar relationship in lake ecosystems 43
lakes12 reservoirs Tropic to Arctic
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Energy flow through trophic levels can be
quantified
Energy flow within a single trophic compartment
Consumption efficiency In/Pn-1 Ecological
efficiency (food chain efficiency) Pn-1/Pn
14/2007
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