9.2 The Conceptual Framework: A Glossary
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(Grimm & Wissel 1997). Therefore, we only use "stability" here as a generic term
for six certain properties of ecological systems Ccf Table 2.1.1). These six properties, which we refer to in the following as "stability properties", are the essence of
the extreme terminological and conceptual diversity of the debate about "stability"
and related issues in ecology (Grimm et al. 1992; Grimm & Wissel 1997; cf. Connell & Sousa 1983).
Constancy and variability
"Constancy" refers to the property of a dynamics to remain essentially unchanged.
"Variability", in turn, is the complementary concept (Pimm 1991). "Variability",
however, also often refers to some statistical measure of variability, i.e. standard
deviation, variance, or a coefficient of variation. In the following we will directly
refer to these statistical measures whenever variability is to be quantified.
Constancy is not, as is often assumed, a simple and merely descriptive concept.
Instead, it requires an initial, basic understanding of the system in question because
what is "essential" must be decided (Jax et al. 1998). This may lead to the (seemingly) paradoxical situation that cyclical or even extremely irregular dynamics are
considered "constant" if the characteristics of the dynamics remain unchanged
over longer periods of time.
Resilience
"Resilience" refers to the property of a dynamics to return to the reference dynamics after a temporary disturbance. Resilience is the most important stability
concept to understand ecological systems because "understanding" implies the
ability to predict reactions to imposed changes. Resilience has two aspects: firstly,
the speed with which the dynamics returns to the reference dynamics (mostly referred to as "elasticity") and secondly, the whole of the states from which the reference dynamics can be reached again after a disturbance (referred to as "domain
of attraction").
Resistance
"Resistance" refers to the property of a dynamics to remain essentially unchanged
despite the presence of disturbances which have the potential to affect changes.
Applying this concept is difficult because it is hardly ever possible to prove that a
certain impact really has the potential to induce (strong) changes, although in the
case considered no (or only weak) changes are observed. We will use the concept
of resistance only in cases where we know of mechanisms at the level of individuals which prevent the individual from reacting (strongly) to certain impacts (e.g.,
by changing the feeding mode).
Persistence
"Persistence" refers to the property of ecological systems to persist over time, i.e.
to be an identifiable unit over a longer period of time (Shrader-Frechette & McCoy
1993; Grimm 1996; lax et al. 1998; Grimm 1998). Persistence is a concept similar
229
(Grimm & Wissel 1997). Therefore, we only use "stability" here as a generic term
for six certain properties of ecological systems Ccf Table 2.1.1). These six properties, which we refer to in the following as "stability properties", are the essence of
the extreme terminological and conceptual diversity of the debate about "stability"
and related issues in ecology (Grimm et al. 1992; Grimm & Wissel 1997; cf. Connell & Sousa 1983).
Constancy and variability
"Constancy" refers to the property of a dynamics to remain essentially unchanged.
"Variability", in turn, is the complementary concept (Pimm 1991). "Variability",
however, also often refers to some statistical measure of variability, i.e. standard
deviation, variance, or a coefficient of variation. In the following we will directly
refer to these statistical measures whenever variability is to be quantified.
Constancy is not, as is often assumed, a simple and merely descriptive concept.
Instead, it requires an initial, basic understanding of the system in question because
what is "essential" must be decided (Jax et al. 1998). This may lead to the (seemingly) paradoxical situation that cyclical or even extremely irregular dynamics are
considered "constant" if the characteristics of the dynamics remain unchanged
over longer periods of time.
Resilience
"Resilience" refers to the property of a dynamics to return to the reference dynamics after a temporary disturbance. Resilience is the most important stability
concept to understand ecological systems because "understanding" implies the
ability to predict reactions to imposed changes. Resilience has two aspects: firstly,
the speed with which the dynamics returns to the reference dynamics (mostly referred to as "elasticity") and secondly, the whole of the states from which the reference dynamics can be reached again after a disturbance (referred to as "domain
of attraction").
Resistance
"Resistance" refers to the property of a dynamics to remain essentially unchanged
despite the presence of disturbances which have the potential to affect changes.
Applying this concept is difficult because it is hardly ever possible to prove that a
certain impact really has the potential to induce (strong) changes, although in the
case considered no (or only weak) changes are observed. We will use the concept
of resistance only in cases where we know of mechanisms at the level of individuals which prevent the individual from reacting (strongly) to certain impacts (e.g.,
by changing the feeding mode).
Persistence
"Persistence" refers to the property of ecological systems to persist over time, i.e.
to be an identifiable unit over a longer period of time (Shrader-Frechette & McCoy
1993; Grimm 1996; lax et al. 1998; Grimm 1998). Persistence is a concept similar