Environmental Engineering Reference
In-Depth Information
TABLE 3.3
Relationships between resource supply and secondary production (or other measures of
consumer activity) in ecosystems. The slope is the reduced major axis slope, not the ordinary least
squares slope.
Ecosystem Type
Measure of Consumer Activity Slope of Relationship Source
Lakes
Macrozoobenthos production
0.8
Kajak et al. (1980)
Aquatic ecosystems
Bacterial production
1.1
Cole et al. (1988)
Terrestrial ecosystems
Above-ground production
1.8
McNaughton et al. (1991)
Aquatic ecosystems
Ingestion by herbivores
1.05
Cebrian and Lartigue (2004)
Terrestrial ecosystems
Ingestion by herbivores
1.8
Cebrian and Lartigue (2004)
Various marine ecosystems Ingestion by herbivores
1
Cebrian (2002)
can be calculated exactly, at least in principle (
Strayer 1988
). Consider an ecosystem that
receives an input of 100 g of organic matter, and is populated by a community of consu-
mers, all of which (for simplicity) have net growth efficiencies of 30%. After all of these
inputs have been assimilated by consumers, 70 g is lost by respiration, and 30 g remains in
the system. Now this 30 g is assimilated in a second round of consumption, resulting in
0.3
9 g of production and 21 g of respiration. This 9 g is then assimilated in a third
round of consumption, giving 2.7 g of production and 6.3 g of respiration. By the time
that the original 100 g of inputs is respired, a secondary production of 30 g
3
30 g
5
1
1
9g
2.7 g
42.86 g will have occurred.
More generally, all organic matter that enters an ecosystem at steady state and is not
lost through nonrespiratory means (e.g., sedimentation, fire, photolysis) must be destroyed
by respiration. (The assumption of steady state is not critical and may be relaxed simply
by adding storage terms to the following equations.) Thus,
1
...
5
S
5
R
1
L
ð
3
:
10
Þ
where
S
is the net supply of organic matter to the ecosystem (i.e., net autochthonous pri-
mary production plus allochthonous inputs) to an ecosystem,
R
is respiration of all consu-
mers, and
L
is nonrespiratory losses. By definition,
ε
g
5
P
=ð
P
1
R
Þ
ð
3
:
11
Þ
where
ε
g
is the net growth efficiency of consumers (the weighted mean;
Strayer 1991
) and
P
is their production. Substituting and solving,
P
5 ð
S
2
L
Þ 3
ε
=ð
2
ε
Þ
ð
:
Þ
1
3
12
g
g
Similarly,
A
5 ð
S
2
L
Þ=ð
1
2
ε
Þ
ð
3
:
13
Þ
g
where
A
is the summed assimilation of all consumers in the ecosystem, and
I
5 ð
S
2
L
Þ=ð
ε
3 ð
1
2
ε
ÞÞ
ð
3
:
14
Þ
a
g
