Principles of terrestrial ecosystem ecology.pdf

times of year (Fisher et al. 1998). Other streams
have discharge peaks associated with snow
melt. Large rivers may overflow their banks
onto a floodplain during periods of high flow.
Many tropical rivers flood annually, so floodplains
alternate between being terrestrial and
aquatic habitats.
The river continuum concept describes an
idealized transition in ecosystem structure and
functioning from narrow headwater streams to
broad rivers (Fig. 10.10) (Vannote et al. 1980).
Headwater streams are often shaded by
terrestrial vegetation. These plants reduce light
availability to aquatic primary producers and
provide most of the organic matter input to
the stream. Leaves and wood that fall into the
Figure 10.10. The river continuum concept
(Vannote et al. 1980). Headwater streams have little
in-stream production (P), so respiration (R) by
decomposers and animals greatly exceeds production.
Coarse particulate organic matter (CPOM)
dominates the detrital pool. Shredders and collectors
are the dominant invertebrates. In middle sections of
rivers, more light is available, and in-stream produc-
Streams and Rivers 239
stream are colonized by aquatic fungi and to a
lesser extent by bacteria (Moss 1998). The
resulting leaf packs that accumulate behind
rocks, logs, and other obstructions are consumed
by invertebrate shredders that break
leaves and other detritus into pieces and digest
the microbial jam on the surface of these particles,
just as occurs in the soil (Wagener et al.
1998). This creates fresh surfaces for microbial
attack and produces feces and other fine material
that is carried downstream. Some of the fine
particles are consumed in suspension by filter
feeders like black fly larvae or from benthic
sediments by collectors like oligochaete worms.
The abundance of algae and their grazers is
limited in headwater streams by low light avail-
tion exceeds respiration. Fine particulate organic
matter (FPOM) is the dominant form of organic
matter, and collectors and grazers are the dominant
organisms. Large rivers accumulate considerable
organic-rich sediments dominated by collectors
feeding on FPOM from upstream. Respiration by
detrital organisms exceeds primary production.