262
I () AssessIng Stahility Properties
Relation to ecological concepts and other ecosystem approaches
Throughout the history of ecology, several attempts were made to understand and
investigate the complexity of ecological systems (Bradbury et al. 1996). ONeill et
al. (1986) distinguish two approaches, a "population-community" and a "processfunctional" approach. The former focuses on organisms and interactions of biota
while the latter targets rates of processes, energy flow and productivity. O'Neill et
al. (1986) suggest a hierarchical approach to ecosystem research, but also the
approach taken in ELA W AT is suitable to combine the "population-community"
and a "process-functional" approaches (Leuschner & Scherer 1989). Therefore the
relevance of processes causing stability properties on popUlation or community
levels has to be assessed for higher hierarchy levels. However, missing long-term
and large-scale studies make the realization of this assessment more difficult
(Chap. 9).
The species with their specific life histories are the active players for stability
properties on the population and community level and for the recolonization after
disturbances. To take this into account, ELA W AT turned away from (super-)
organismic approaches (Richardson 1980) and was more related to the individualistic concept of Gleason (1939) (Dittmann et al. 1997). This dispute also fuelled a
workshop on concepts of ecosystem (see articles in Dittmann et al. 1996). Starting
off with a given stability property in the title of ELA W AT, a lively debate developed in the course of the project about the (non-)existence of emergent properties
at the ecosystem level and whether the Wadden Sea can have emergent properties
at all.
The analysis of stability properties is closely related with several ecological
concepts addressing the relevance of disturbances in ecosystems and succession.
These are the patch-dynamic (Pickett & White 1985, Paine & Levin 1981) and the
mosaic-cylce theory (Remmert 1991). However, it was disputed whether these
concepts can be applied to the ecology of the soft-sediment realm of the Wadden
Sea (see Chap. 8).
The discussion on "stability" can be followed throughout the ecological literature of the past decades (MacArthur 1955; May 1971; Holling 1973; Orians 1975;
Gray 1977; Pimm 1984; Grimm et al. 1992). The most often debated relation
between diversity and complexity with stability properties was not a topic in
ELA W A T. To apply stability concepts for the analysis of an ecosystem, the
"checklist" by Grimm et al. (1992) was useful for focusing on clearly defined
ecological situations. "Stability" encompasses a number of properties (Grimm &
Wissel 1997) and those specified in ELA WAT are defined in Chap. 9.
Realization of the approach
The realization of the approach of ELA W AT which focussed on qualitative properties required a proper way to handle the concept (Bradbury et al. 1986), a
knowledge of theoretical backgrounds by all scientists involved and a spatial and
temporal frame of the project adjusted to the topic.
The methods used in ELA WAT to analyse stability properties and mechanisms
encompassed the techniques developed by mathematicians to analyse and compare
I () AssessIng Stahility Properties
Relation to ecological concepts and other ecosystem approaches
Throughout the history of ecology, several attempts were made to understand and
investigate the complexity of ecological systems (Bradbury et al. 1996). ONeill et
al. (1986) distinguish two approaches, a "population-community" and a "processfunctional" approach. The former focuses on organisms and interactions of biota
while the latter targets rates of processes, energy flow and productivity. O'Neill et
al. (1986) suggest a hierarchical approach to ecosystem research, but also the
approach taken in ELA W AT is suitable to combine the "population-community"
and a "process-functional" approaches (Leuschner & Scherer 1989). Therefore the
relevance of processes causing stability properties on popUlation or community
levels has to be assessed for higher hierarchy levels. However, missing long-term
and large-scale studies make the realization of this assessment more difficult
(Chap. 9).
The species with their specific life histories are the active players for stability
properties on the population and community level and for the recolonization after
disturbances. To take this into account, ELA W AT turned away from (super-)
organismic approaches (Richardson 1980) and was more related to the individualistic concept of Gleason (1939) (Dittmann et al. 1997). This dispute also fuelled a
workshop on concepts of ecosystem (see articles in Dittmann et al. 1996). Starting
off with a given stability property in the title of ELA W AT, a lively debate developed in the course of the project about the (non-)existence of emergent properties
at the ecosystem level and whether the Wadden Sea can have emergent properties
at all.
The analysis of stability properties is closely related with several ecological
concepts addressing the relevance of disturbances in ecosystems and succession.
These are the patch-dynamic (Pickett & White 1985, Paine & Levin 1981) and the
mosaic-cylce theory (Remmert 1991). However, it was disputed whether these
concepts can be applied to the ecology of the soft-sediment realm of the Wadden
Sea (see Chap. 8).
The discussion on "stability" can be followed throughout the ecological literature of the past decades (MacArthur 1955; May 1971; Holling 1973; Orians 1975;
Gray 1977; Pimm 1984; Grimm et al. 1992). The most often debated relation
between diversity and complexity with stability properties was not a topic in
ELA W A T. To apply stability concepts for the analysis of an ecosystem, the
"checklist" by Grimm et al. (1992) was useful for focusing on clearly defined
ecological situations. "Stability" encompasses a number of properties (Grimm &
Wissel 1997) and those specified in ELA WAT are defined in Chap. 9.
Realization of the approach
The realization of the approach of ELA W AT which focussed on qualitative properties required a proper way to handle the concept (Bradbury et al. 1986), a
knowledge of theoretical backgrounds by all scientists involved and a spatial and
temporal frame of the project adjusted to the topic.
The methods used in ELA WAT to analyse stability properties and mechanisms
encompassed the techniques developed by mathematicians to analyse and compare