Environmental Engineering Reference
In-Depth Information
CHAPTER
3
Secondary Production and Consumer
Energetics
David L. Strayer
Cary Institute of Ecosystem Studies, Millbrook, NY
INTRODUCTION
The energy captured by primary production supports animals, fungi, and heterotrophic
bacteria and protozoans, which together constitute the community of consumers in ecosys-
tems. These consumers include species that we harvest from the wild, species that we
value for recreational or aesthetic reasons, and nuisance species. Consumers play two key
roles in ecosystem energetics. Their respiration destroys the organic matter that serves as
the medium of energy exchange in ecosystems, and thereby regenerates nutrients trapped
in organic matter. This important role will be discussed in the next chapter on decomposi-
tion. However, not all the organic matter that a consumer eats is respired; some is cap-
tured and used for growth and reproduction of the consumer, which we call secondary
production. This material is available to move up the food web. In this chapter, we will
explore the basic energy budget of consumers and its ecological significance, and discuss
the controls and prediction of secondary production, a particularly important and well
studied part of consumer energetics. Finally, we will discuss briefly aspects of nutrient
flow through consumer populations.
CONSUMER ENERGETICS
The Energy Budget of Consumers
Although there are many possible ways to budget energy flow through a consumer, a
useful and widely used scheme is shown in
Figure 3.1
. Energy in food ingested (
I
)bya
consumer may be either assimilated (
A
) or lost through egestion (
E
, sometimes called
F
,
