224
8 Grid Based Modellin&
Moreover, the models presented in this chapter underscore the plea of Michaelis
& Bbhme (1994) for more detailed studies of individual, dominant macrozoobenthic species, for example L. conchilega and M. edulis. In any case, emphasis must
be focused even more strongly on abiotic factors than was the case in the
ELA W AT project, in particular on the hydrodynamic regime. This would mean
both empirical studies of tidal currents and swell, and oceanographic models. It
would in principle be possible to adapt the large-scale oceanographic model, which
was parameterized for the Wadden Sea at the end of the ELA W A T project
(Chap. 3.3), to the sandtlat shown in Fig. 8.4.1. The same spatial resolution could
be used as in TOPOGRID. We see such a combination of grid-based ecological
modelling, an oceanographic model, measurements of the current regime at certain
points, and experimental studies of the macrozoobenthic species, as a promising
direction of future research of macrozoobenthos in tidal flat ecosystems.
Models are not ends in themselves but a means to an end. At the present state of
knowledge of benthic research, the purpose of modelling is more to focus on the
most important gaps in our knowledge and to explore effective ways of closing
these gaps (see above) than to give definite answers. Moreover, the attempt to
make a group of experts formulate a model like TOPOGRID, for example at an
informal, interdisciplinary workshop, would be an ideal means for an efficient
communication beyond one's own discipline.
With these conclusions we tried to outline the actual potentials and limitations
of spatially explicit, grid-based ecological models in the Wadden Sea. But since
models are still often misinterpreted as "prediction machines", we would like to
emphasize here an additional principle limitation of ecological models - namely,
that deterministic predictions of the distribution pattern are impossible (cf.
Fig. 8.4.4). Ecological models can, at best, reveal principle mechanisms and predict certain probabilities of certain outcomes.
8.6
Ecological Conclusions
Concerning the ecological concepts mentioned in 8.1.1, we are uncertain whether
the concept of patch-dynamics or the theory of mosaic-cycles are directly applicable to the Wadden Sea. In the past, the concept of patch-dynamics was too uncritically transferred from marine hard bottoms to soft bottoms. Important basic differences between these two habitat types were not adequately considered. Frid and
Townsend (1989) stress that patch-dynamics may only be invoked as an underlying
mechanism which structures ecological systems if the organisms in question are
sessile, e.g. plants or sessile benthic organisms living on hard substrate (barnacles,
molluscs, etc.). In such systems, space is evidently a limiting resource. In addition,
the local consequences of disturbance events remain visible and ecologically effective for a longer period of time. In contrast, on the soft bottoms of the intertidal
of the Wadden Sea the limiting resource is more difficult to identify. Most organisms are so mobile that they may escape local competition. This mobility and the
"great equalizer", the tidal currents, ensure that the local effects of disturbance
events are only short-lived.
8 Grid Based Modellin&
Moreover, the models presented in this chapter underscore the plea of Michaelis
& Bbhme (1994) for more detailed studies of individual, dominant macrozoobenthic species, for example L. conchilega and M. edulis. In any case, emphasis must
be focused even more strongly on abiotic factors than was the case in the
ELA W AT project, in particular on the hydrodynamic regime. This would mean
both empirical studies of tidal currents and swell, and oceanographic models. It
would in principle be possible to adapt the large-scale oceanographic model, which
was parameterized for the Wadden Sea at the end of the ELA W A T project
(Chap. 3.3), to the sandtlat shown in Fig. 8.4.1. The same spatial resolution could
be used as in TOPOGRID. We see such a combination of grid-based ecological
modelling, an oceanographic model, measurements of the current regime at certain
points, and experimental studies of the macrozoobenthic species, as a promising
direction of future research of macrozoobenthos in tidal flat ecosystems.
Models are not ends in themselves but a means to an end. At the present state of
knowledge of benthic research, the purpose of modelling is more to focus on the
most important gaps in our knowledge and to explore effective ways of closing
these gaps (see above) than to give definite answers. Moreover, the attempt to
make a group of experts formulate a model like TOPOGRID, for example at an
informal, interdisciplinary workshop, would be an ideal means for an efficient
communication beyond one's own discipline.
With these conclusions we tried to outline the actual potentials and limitations
of spatially explicit, grid-based ecological models in the Wadden Sea. But since
models are still often misinterpreted as "prediction machines", we would like to
emphasize here an additional principle limitation of ecological models - namely,
that deterministic predictions of the distribution pattern are impossible (cf.
Fig. 8.4.4). Ecological models can, at best, reveal principle mechanisms and predict certain probabilities of certain outcomes.
8.6
Ecological Conclusions
Concerning the ecological concepts mentioned in 8.1.1, we are uncertain whether
the concept of patch-dynamics or the theory of mosaic-cycles are directly applicable to the Wadden Sea. In the past, the concept of patch-dynamics was too uncritically transferred from marine hard bottoms to soft bottoms. Important basic differences between these two habitat types were not adequately considered. Frid and
Townsend (1989) stress that patch-dynamics may only be invoked as an underlying
mechanism which structures ecological systems if the organisms in question are
sessile, e.g. plants or sessile benthic organisms living on hard substrate (barnacles,
molluscs, etc.). In such systems, space is evidently a limiting resource. In addition,
the local consequences of disturbance events remain visible and ecologically effective for a longer period of time. In contrast, on the soft bottoms of the intertidal
of the Wadden Sea the limiting resource is more difficult to identify. Most organisms are so mobile that they may escape local competition. This mobility and the
"great equalizer", the tidal currents, ensure that the local effects of disturbance
events are only short-lived.