References
225
Our first model confirms these considerations. It was difficult to identify a defined "natural" spatial unit which could serve as a building block for a grid-based
model. "Patch-dynamics" should therefore only be considered as a general framework for explaining the distribution and abundance of macrozoobenthic species in
the intertidal of the Wadden Sea. This framework "acknowledge[s] the existence
of significant variation in community structure, often over relatively small spatial
scales" (Downes 1990, p. 41 I).
Similarly, the theory of mosaic-cycles is not applicable to the Wadden Sea and
its soft bottom communities (cL Reise 1991). There are no local "cycles" of communities. At best, one could speak of "erratic" cycles (Reise 1991), i.e. the sequence of communities in a "cycle" is not predictable. Moreover, there is no largescale equilibrium of the distribution and abundance of macrozoobenthic species in
the Wadden Sea. Therefore, concepts and theories which, like the theory of mosaic-cycles, assume or aim at equilibria are not suitable for exploring benthic
communities of the Wadden Sea.
The two models presented in this chapter demonstrate that any such exploration
has to start with the concept of a zonation pattern which follows an abiotically
determined gradient. In contrast to rocky shores, however, "zonations" in the
Wadden Sea are more variable in space and time because of the three-dimensional
abiotic gradients, the disturbance regime and the high mobility of the organism
(Raffaelli & Hawkins 1996). Interactions between macrozoobenthic species are
probably not very strong ~ if compared to the key role some predators or competitors play on rocky shores. Nevertheless they may, as has been suggested by our
models, have considerable influence on the distribution pattern.
Acknowledgements
We would like to thank Thomas Leu for his contribution to the first model, and
Michael Reetz and Udo Hubner for the topographic map of the Spiekeroog backbarrier tidal flat in computer-readable form. We thank the reviewer for helpful
comments on the manuscript. The project was funded by the German Bundesministerium fur Bildung, Wissenschaft, Forschung und Technologie (BMBF) under
grant number 03FOII2 A and B. The responsibility for the contents of the publication rests with the authors.
References
Crick F (1988) What made pursuit. Basic Books. New York.
Downes BJ (1990) Patch dynamics and mobility of fauna in streams and other habitats.
Oikos 59: 411-413.
Dories J (1978) Das Watt als Lebensraum. In: Reineck H-E (Ed) Das Watt. Ablagerungs- und
Lebensraum, Waldemar Kramer, Frankfurt. pp 107-143
Frid CLl, Townsend CR (1989) An appraisal of the patch dynamics concept in stream and marine benthic communities whose members are highly mobile. Oikos 56: 137-141
Grimm Y (1994) Mathematical models and understanding in ecology. Ecol Model 75176: 641651
Grimm Y, Frank K, Jeltsch F. Brandl R. Uchmanski J, Wissel C (1996) Pattern-oriented modelling in population ecology. Sci Total Environm 183: 151-166
225
Our first model confirms these considerations. It was difficult to identify a defined "natural" spatial unit which could serve as a building block for a grid-based
model. "Patch-dynamics" should therefore only be considered as a general framework for explaining the distribution and abundance of macrozoobenthic species in
the intertidal of the Wadden Sea. This framework "acknowledge[s] the existence
of significant variation in community structure, often over relatively small spatial
scales" (Downes 1990, p. 41 I).
Similarly, the theory of mosaic-cycles is not applicable to the Wadden Sea and
its soft bottom communities (cL Reise 1991). There are no local "cycles" of communities. At best, one could speak of "erratic" cycles (Reise 1991), i.e. the sequence of communities in a "cycle" is not predictable. Moreover, there is no largescale equilibrium of the distribution and abundance of macrozoobenthic species in
the Wadden Sea. Therefore, concepts and theories which, like the theory of mosaic-cycles, assume or aim at equilibria are not suitable for exploring benthic
communities of the Wadden Sea.
The two models presented in this chapter demonstrate that any such exploration
has to start with the concept of a zonation pattern which follows an abiotically
determined gradient. In contrast to rocky shores, however, "zonations" in the
Wadden Sea are more variable in space and time because of the three-dimensional
abiotic gradients, the disturbance regime and the high mobility of the organism
(Raffaelli & Hawkins 1996). Interactions between macrozoobenthic species are
probably not very strong ~ if compared to the key role some predators or competitors play on rocky shores. Nevertheless they may, as has been suggested by our
models, have considerable influence on the distribution pattern.
Acknowledgements
We would like to thank Thomas Leu for his contribution to the first model, and
Michael Reetz and Udo Hubner for the topographic map of the Spiekeroog backbarrier tidal flat in computer-readable form. We thank the reviewer for helpful
comments on the manuscript. The project was funded by the German Bundesministerium fur Bildung, Wissenschaft, Forschung und Technologie (BMBF) under
grant number 03FOII2 A and B. The responsibility for the contents of the publication rests with the authors.
References
Crick F (1988) What made pursuit. Basic Books. New York.
Downes BJ (1990) Patch dynamics and mobility of fauna in streams and other habitats.
Oikos 59: 411-413.
Dories J (1978) Das Watt als Lebensraum. In: Reineck H-E (Ed) Das Watt. Ablagerungs- und
Lebensraum, Waldemar Kramer, Frankfurt. pp 107-143
Frid CLl, Townsend CR (1989) An appraisal of the patch dynamics concept in stream and marine benthic communities whose members are highly mobile. Oikos 56: 137-141
Grimm Y (1994) Mathematical models and understanding in ecology. Ecol Model 75176: 641651
Grimm Y, Frank K, Jeltsch F. Brandl R. Uchmanski J, Wissel C (1996) Pattern-oriented modelling in population ecology. Sci Total Environm 183: 151-166