6
2 ELA W AT: Goals and Conceptual Framework
in particular the case regarding the long-term pattern of large-scale zonations of
sediment types with their associated biota, which is determined by abiotic factors
and biotic interactions. The programme of ELA W A T was to study the mechanisms of this persistence. Understanding how the Wadden Sea has "managed" to
maintain its - still to be defined - properties and characteristics over a long time
will enable an evaluation of the present state of the Wadden Sea and may also
allow forecasts concerning its future development.
Conceptual development in ELA W AT was originally based on the working hypothesis "stability by variability" (ARSU 1989), which was subsequently replaced
because of its vagueness by an emphasis on spatial and temporal patterns of biotic
and abiotic components of the Wadden Sea as well as natural disturbances related
to these patterns (Jax et al. 1993). The distribution of species in the Wadden Sea
and their association into defined communities reflect the patchy distribution of
resources, local interactions between species and local effects of specific disturbances. These distribution patterns exhibit temporal variation on a short-term, a
seasonal, and a long-term scale. What processes are relevant for the development
of specific temporal and spatial patterns and what effects disturbances have on the
patterns and thus on the entire system were the central topics of ELA W A T. Based
on the analysis of regeneration following specific disturbance events, stability
properties (resilience, persistence) were to be identified (Table 2.1. I and see
Chap. 9). Therefore the sub-projects of ELA W A T carried out investigations and
experiments at several hierarchy levels and in various compartments of the ecosystem Wadden Sea.
The common perspective for analysing the results of the sub-projects was the
assessment of stability properties. To our knowledge this is the first attempt to use
stability properties, instead of energy flow, for the development of an integrated
view of an ecosystem, i.e. of a landscape complete with all the components and
processes involved therein. In this sense ELA WAT was a methodological pilot
study, which - asides from the defined aims concerning the Wadden Sea - could
set a new direction for future ecosystem analyses.
Table 2.1.1 Overview on the most important stability concepts and -properties in ecology. After
Grimm et al. 1992 and Grimm 1996
Stability
property
Definition
Constancy
Remaining essentially unchanged
Resistance
Remaining essentially unchanged despite the presence
of disturbances
Resilience
Returning to the reference state (or dynamic) after a
temporary disturbance
Elasticity
Speed of return to the reference state (or dynamic) after
a temporary disturbance
Persistence Persistence over time of an ecological system
2 ELA W AT: Goals and Conceptual Framework
in particular the case regarding the long-term pattern of large-scale zonations of
sediment types with their associated biota, which is determined by abiotic factors
and biotic interactions. The programme of ELA W A T was to study the mechanisms of this persistence. Understanding how the Wadden Sea has "managed" to
maintain its - still to be defined - properties and characteristics over a long time
will enable an evaluation of the present state of the Wadden Sea and may also
allow forecasts concerning its future development.
Conceptual development in ELA W AT was originally based on the working hypothesis "stability by variability" (ARSU 1989), which was subsequently replaced
because of its vagueness by an emphasis on spatial and temporal patterns of biotic
and abiotic components of the Wadden Sea as well as natural disturbances related
to these patterns (Jax et al. 1993). The distribution of species in the Wadden Sea
and their association into defined communities reflect the patchy distribution of
resources, local interactions between species and local effects of specific disturbances. These distribution patterns exhibit temporal variation on a short-term, a
seasonal, and a long-term scale. What processes are relevant for the development
of specific temporal and spatial patterns and what effects disturbances have on the
patterns and thus on the entire system were the central topics of ELA W A T. Based
on the analysis of regeneration following specific disturbance events, stability
properties (resilience, persistence) were to be identified (Table 2.1. I and see
Chap. 9). Therefore the sub-projects of ELA W A T carried out investigations and
experiments at several hierarchy levels and in various compartments of the ecosystem Wadden Sea.
The common perspective for analysing the results of the sub-projects was the
assessment of stability properties. To our knowledge this is the first attempt to use
stability properties, instead of energy flow, for the development of an integrated
view of an ecosystem, i.e. of a landscape complete with all the components and
processes involved therein. In this sense ELA WAT was a methodological pilot
study, which - asides from the defined aims concerning the Wadden Sea - could
set a new direction for future ecosystem analyses.
Table 2.1.1 Overview on the most important stability concepts and -properties in ecology. After
Grimm et al. 1992 and Grimm 1996
Stability
property
Definition
Constancy
Remaining essentially unchanged
Resistance
Remaining essentially unchanged despite the presence
of disturbances
Resilience
Returning to the reference state (or dynamic) after a
temporary disturbance
Elasticity
Speed of return to the reference state (or dynamic) after
a temporary disturbance
Persistence Persistence over time of an ecological system