7 Grazers as Sources and Sinks for Nutrients:
Conclusions, Limitations, and Speculations
If further progress should be possible, then
more complex models are needed. ... Also,
the trophic-dynamic interrelationships in the
sense of Lindeman (1942) requires much
more sophisticated analyses.
R. A. Vollenweider (1976).
The trophic-dynamic school in ecology, pioneered by Lindeman (1942), has
typically used mass or energy equivalents for the quantitative description of
interactions between trophic levels. Progress in the direction envisioned by
Vollenweider (1976), of coupling input-output models with a trophicdynamic view of ecosystems, would require also the consideration of flows of
limiting nutrients among trophic levels. The flow networks of energy and
essential elements cannot be simple mirror images of each other, since, for
example, energy flows unidirectionally from autotrophs to herbivores, while
nutrients flow bidirectionally between the same two trophic levels. As pointed
out by Reiners (1986), the energetic and stoichiometric views of ecosystem
organization, as expressed by e.g., Odum (1957) and Redfield (1958), must
therefore be seen as complementary and irreducible parts of models
describing trophic relationships in nutrient-limited ecosystems.
Herbivorous zooplankton hold a key position in pelagic food webs both by
consuming primary producers, and by supplying regenerated nutrients supporting primary production. Exploring this important dualism in the functional role of zooplankton, as both sources and sinks for nutrients, has been a
central theme throughout this work. This analysis has been facilitated by
applying the homeostatic view of zooplankton stoichiometry supported by
Sterner (1990) and Andersen and Hessen (1991): that the element composition of zooplankton can be considered constant and species-specific, at least
compared to the wide variability of elemental ratios found in the unicellular
organisms constituting their food. In Chapter 2 of this work, it is shown that
this hypothesis leads to a general representation of nutrient cycling and
nutrient partitioning in plankton communities, that can be regarded as a
direct extension of the one-compartment phosphorus loading model of
Vollenweider (1976).
Whether the zooplankton acts as a source or a sink for nutrients in a
specific situation depends on both the temporal scale and on the frame of
reference. Nutrients contained in an individual zooplankter will have a high
likelihood of being lost from the pelagic zone upon death of the organism.
Hence, on a sufficiently long-term scale, zooplankton will always represent a
Conclusions, Limitations, and Speculations
If further progress should be possible, then
more complex models are needed. ... Also,
the trophic-dynamic interrelationships in the
sense of Lindeman (1942) requires much
more sophisticated analyses.
R. A. Vollenweider (1976).
The trophic-dynamic school in ecology, pioneered by Lindeman (1942), has
typically used mass or energy equivalents for the quantitative description of
interactions between trophic levels. Progress in the direction envisioned by
Vollenweider (1976), of coupling input-output models with a trophicdynamic view of ecosystems, would require also the consideration of flows of
limiting nutrients among trophic levels. The flow networks of energy and
essential elements cannot be simple mirror images of each other, since, for
example, energy flows unidirectionally from autotrophs to herbivores, while
nutrients flow bidirectionally between the same two trophic levels. As pointed
out by Reiners (1986), the energetic and stoichiometric views of ecosystem
organization, as expressed by e.g., Odum (1957) and Redfield (1958), must
therefore be seen as complementary and irreducible parts of models
describing trophic relationships in nutrient-limited ecosystems.
Herbivorous zooplankton hold a key position in pelagic food webs both by
consuming primary producers, and by supplying regenerated nutrients supporting primary production. Exploring this important dualism in the functional role of zooplankton, as both sources and sinks for nutrients, has been a
central theme throughout this work. This analysis has been facilitated by
applying the homeostatic view of zooplankton stoichiometry supported by
Sterner (1990) and Andersen and Hessen (1991): that the element composition of zooplankton can be considered constant and species-specific, at least
compared to the wide variability of elemental ratios found in the unicellular
organisms constituting their food. In Chapter 2 of this work, it is shown that
this hypothesis leads to a general representation of nutrient cycling and
nutrient partitioning in plankton communities, that can be regarded as a
direct extension of the one-compartment phosphorus loading model of
Vollenweider (1976).
Whether the zooplankton acts as a source or a sink for nutrients in a
specific situation depends on both the temporal scale and on the frame of
reference. Nutrients contained in an individual zooplankter will have a high
likelihood of being lost from the pelagic zone upon death of the organism.
Hence, on a sufficiently long-term scale, zooplankton will always represent a