Environmental Engineering Reference
In-Depth Information
2001
). Furthermore, ecologists rarely measure secondary production by all consumers in
an ecosystem, so there are few data to compare with these estimates (but see
Table 3.4
).
Nevertheless, this analysis gives four interesting conclusions:
Secondary production is large compared with primary production. If
0.3, then
secondary production is 43% of net organic inputs. It is even possible for secondary
production to exceed primary production (if
ε
g
5
0.5). These numbers are much greater
than the 10% figure often assumed by ecologists, based on a misapplication of
Lindeman's old conclusions.
ε
g
.
Consequently, decomposers use a lot of consumer tissue; their diets are not necessarily
dominated by plant tissue.
Total secondary production may be smaller in systems dominated by homeotherms
than those dominated by poikilotherms.
The energy available for assimilation and ingestion by consumers is generally much
greater than net organic inputs to an ecosystem.
CONCLUSION
Let me close with three points about the controls and prediction of secondary production.
First, perhaps counterintuitively, it is easier to predict the production of a guild of consu-
mers than the production of a single population, and easier still to predict the production of
the entire consumer community. If the biomass of a consumer population is unknown, then
its production is essentially unpredictable. Even if consumer biomass is known, production
TABLE 3.4
Total secondary production (g C m
22
yr
21
) in Mirror Lake,
New Hampshire, estimated from direct measurements and by indirect
means, using the equations in the text.
Direct Estimate
Pelagic bacteria
6
Benthic bacteria
10.5
Metazoan plankton
2.5
Metazoan benthos
6
Fish
0.2
Total direct estimate
25.2
Indirect Estimate
Net organic inputs (
S
)
60
Nonrespiratory losses (
L
)
24.9
Assumed net growth efficiency (
ε
g
)
0.4
Total indirect estimate (
P
)
23.4
Modified from
Strayer (1988)
, using data from
Jordan et al. (1985)
.
