BIOS 3010: Ecology
Lecture 18: Community matter & energy flux:
•  Lecture summary:
–  Matter and energy.
The Hubbard Brook Ecosystem Study
–  Primary
productivity.
–  Trophic structure
–  Flux of matter.
–  Geochemical
cycles.
–  Hubbard Brook.
http://www.hubbardbrook.org/
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 1
2. Matter and energy:
•  All organisms require matter for construction, and
energy for activity, at individual, population and
community levels of organization.
•  Communities interact with the abiotic environment
as ecosystems which include:
–  primary producers, decomposers and detritivores, a pool
of dead organic matter, herbivores, carnivores and
parasites, plus the physicochemical environment that
provides living conditions and acts both as a source and a
sink for energy and matter.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 2
3. Matter and energy:
•  The primary productivity of a community is:
–  The rate at which biomass is produced per unit
area by plants (primary producers) as energy
(J·m-2·day-1) or dry organic matter (kg·ha-1·year-1).
•  Gross primary productivity (GPP)
–  Total fixation of energy by photosynthesis
•  Net primary productivity (NPP)
–  GPP - energy lost to respiration
»  = actual rate of biomass accumulation available for
consumption by heterotrophs.
•  Secondary productivity
–  Rate of biomass production by heterotrophs.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 3
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4. Primary productivity:
•  Global terrestrial NPP:
–  110 - 120 x 109 tonnes dry weight per year
•  Global marine NPP (Fig. 18.1, Table 18.1):
–  50 - 60 x 109 tonnes per year
•  despite being 67% of the earth's surface
•  Productivity (P) and biomass (B) (Fig. 17.6):
–  P:B ratios (kg/year/kg biomass) average:
•
•
•
•
0.042 for forests
0.29 for other terrestrial systems
17 for aquatic communities.
Ratios also change with successional shifts (Fig. 18.6).
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 4
5. Community trophic structure:
•  Energy moves through communities via trophic
(feeding) interactions.
•  Primary productivity generates secondary
productivity in heterotrophic consumers once
they consume autotrophs with a measurable
efficiency:
–  The slope of Fig. 18.17 at about 0.1.
•  Generates the classical view of a broad-based
productivity pyramid or biomass pyramid:
–  After Elton (1927) and later Lindemann (1942).
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 5
6. Community trophic structure:
•  Basic trophic structure of communities (Figs 17.21
& 17.22).
•  Energy flow through different components of a
grassland community (Fig. 18.22).
•  Predicted vs observed values of productivity
(Fig. 18.23).
•  Energy flow & nutrient cycling links between
decomposer & grazer systems & return of free
inorganic nutrients released by decomposers
from dead organic matter (DOM) back to net
primary production (NPP) (Fig. 18.1).
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 6
2
7. NPP and global climate change
•  Climate models predict that increased
greenhouse gases will lead to an
increase in temperature of 1.5-4.5°C.
•  Altered CO2, temperature, cloud cover and
rainfall will dramatically change the NPP
of earth's communities Table 18.6.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 7
8. Flux of matter (chapter 19):
•  “If plants, and their consumers, were not
eventually decomposed, the supply of
nutrients would become exhausted and
life on earth would cease.”
•  So the matter cycling (fueled by energy) of
Fig. 18.1 is essential.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 8
9. Biogeochemical cycles:
•  Terrestrial and aquatic ecosystems are
linked much as in Fig. 18.2.
•  Within these links, the primary resources of
water, phosphorus, nitrogen, sulfur and
carbon circulate as in Figs 18.19, 18.20
& 18.21.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 9
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10. The Hubbard Brook experiments:
–  Within a water catchment area how important is
nutrient cycling within the terrestrial community in
relation to the through-put of nutrients?
–  The Hubbard Brook experiment in the temperate
deciduous forest of the White Mountains in New
Hampshire is the best test of this question:
•  6 small catchments with input and output measured
(Table 18.1).
•  Most nutrients were held in biomass (like N2 in Fig. 19.5).
•  But sulfur was released in excess of input because it was
a major pollutant in the area (acid rain).
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 10
11. The Hubbard Brook experiments:
•  Experimentally, one catchment was deforested:
–  The rate of nutrient loss rose x13 in comparison
with a control catchment.
–  Two reasons for the lost nutrients:
•  (1) through increased water flow (less water held by
trees) - see Fig. 19.4
•  (2) within-system nutrient cycling was lost by
uncoupling the decomposition process from the
plant-uptake process
–  nutrients made available by decomposition were lost to
leaching in the increased stream flow (Fig. 18.6).
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 11
BIOS 3010: Ecology
Lecture 18: slide 12
Figure 18.1 (3rd ed.):
Distribution of
global terrestrial
and marine net
primary
productivity
Dr. S. Malcolm
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(3rd ed.)
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 13
Figure 17.6: Relationship between average net
primary productivity and average standing crop
biomass for communities in Table 18.1
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 14
Figure 18.6 (3rd ed.): Change in net primary
productivity (P), standing crop biomass (B) and
P:B ratio during forest succession on Long Island.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 15
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Figure 18.17 (3rd ed.): Secondary productivity plotted
against primary productivity in three communities.
(see Fig 17.20, 4th ed.)
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 16
BIOS 3010: Ecology
Lecture 18: slide 17
Figure 17.21:
Energy flow
through a trophic
compartment.
Dr. S. Malcolm
Figure 17.22: Model of trophic structure and
energy flow for a terrestrial community.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 18
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Figure 18.22 (3rd ed.): Patterns of energy flow through
the different trophic compartments of Fig. 17.22.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 19
Figure 18.23 (3rd ed.): Predicted heterotroph
productivity plotted against observed
productivity in a range of communities.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 20
Figure 18.1: Energy flow (pink) and nutrient cycling
of organic matter (red) and inorganic matter (white).
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 21
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(3rd ed.)
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 22
BIOS 3010: Ecology
Lecture 18: slide 23
Figure 18.2:
Components of
nutrient budgets
of terrestrial and
aquatic systems.
Dr. S. Malcolm
Figure 18.19: Hydrological cycle.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 24
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Figure 18.20: Major global pathways of nutrients
between abiotic and biotic reservoirs.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 25
BIOS 3010: Ecology
Lecture 18: slide 26
BIOS 3010: Ecology
Lecture 18: slide 27
Figure 18.21:
Four main
pathways of
nutrient flux
(black arrows)
and human
perturbations
(red arrows).
Dr. S. Malcolm
Table 18.1:
Dr. S. Malcolm
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Figure 19.5 (3rd ed.): Annual nitrogen budget for
control forest at Hubbard Brook (kg N2/ha).
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 28
Figure 19.4 (3rd ed.): Annual loss of major
nutrients in streamflow.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 29
BIOS 3010: Ecology
Lecture 18: slide 30
Figure 18.6:
Concentrations of ions in
stream water from
control and deforested
watersheds at Hubbard
Brook.
Dr. S. Malcolm
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The Hubbard Brook Ecosystem Study:
http://www.hubbardbrook.org/
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 18: slide 31
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