Environmental Engineering Reference
In-Depth Information
can be predicted only approximately. The production of a guild of consumers often is con-
strained and predictable (at least loosely) by food supply. Finally, at the level of the entire
consumer community, budgetary constraints tightly define the relationship among organic
inputs, consumer activity, and nonrespiratory losses from the ecosystem, allowing for direct
(if approximate) calculation of production of all consumers in the ecosystem. Thus, it is pos-
sible to predict the secondary production of all consumers on Earth more precisely than the
production of an arbitrary individual population in a local ecosystem. This surprising result
occurs because once we move up to the ecosystem level, we are able to apply powerful
mass-balance constraints to the solution of the problem.
Second, expressing the total secondary production in an ecosystem by
Eq. (3.12)
high-
lights the linkages between consumer energetics and other aspects of ecosystem ecology.
Obviously, consumer production depends on the supply of organic matter and nutrients
to an ecosystem, including both autochthonous production and allochthonous inputs of
organic matter and nutrients. Perhaps less obviously, consumer production also depends
on processes that consume (e.g., fire), retain (e.g., debris dams), or export (e.g., floods)
organic matter in an ecosystem. Likewise, the amount of organic matter that is buried,
exported from an ecosystem, or is available to nonrespiratory fates (e.g., fire) depends on
the number and physiological characteristics of consumers. Thus, consumers, exports, and
nonrespiratory losses can be thought of as competitors for organic matter, and consumer
activity is at the center of an interaction web that extends well beyond energetics. For
instance,
Rivkin and Legendre (2001)
noted that bacterial respiration in the open ocean
helps to determine how much organic matter sinks to the ocean depths and how much
CO
2
is exported to the atmosphere.
Third, by comparison with primary production, there has been little explicit consider-
ation of the controls and prediction of secondary production. To the extent that these
topics have been considered, attention has been focused on the production of individual
populations of animals or sometimes on guilds of consumers rather than on the entire
community of producers. However, when secondary production is considered at the same
level of aggregation as primary production (whole communities, not individual popula-
tions), it becomes more or less predictable. To a first approximation, secondary production
at the community level appears to be controlled by the amount of organic matter supplied
to the ecosystem, by the ability of the ecosystem to retain versus export organic matter,
and by the importance of competing, nonrespiratory losses (e.g., fire). Further, it seems
clear that resource quality and the availability of inorganic nutrients affect the secondary
production of communities. Thus, at least roughly in parallel to primary production, rates
of secondary production at the community level seem to be controlled by inputs of energy
and a few key nutrients.
References
Banse, K., Mosher, S., 1980. Adult body mass and annual production/biomass relationships of field populations.
Ecol. Monogr. 50, 355
379.
Benke, A.C., 1984. Secondary production of aquatic insects. In: Resh, V.H., Rosenberg, D.M. (Eds.), Ecology of
aquatic insects. Praeger Publishers, New York, pp. 289
322.
