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Synthesis
Initiated by Cole (1954), strategic thinking in ecology resides upon the
concepts of allocation and strategy (Korfiatis and Stamou 1994). The corner
hypothesis underlying the development of schemata describing life history
strategies is rather simple: a limited amount of time and energy is available
throughout organisms' life. Hence, limited quantities should be invested in
various life cycle attributes in such a way as to achieve optimal adaptation of
organisms to environmental constraints. Obviously, the timing of life cycles
and the patterns of energy allocation drive the development of adaptive strategies, i.e. the development of those life history traits which maximise the
fitness of organisms. Thus, adaptive strategies are viewed as responses of
organisms to genetic and environmental constraints resulting in trade-offs
among life history characteristics.
The life history model most familiar to ecologists is that of r-K selection.
First introduced by MacArthur and Wilson in 1967, this model captured the
concept of life history strategies and overwhelmed strategic thinking until
the late 1970s. Pianka (1970) introduced the schema of the r-K line continuum on which species can be classified according to the number of produced
eggs and the survival of juveniles. According to model predictions, near the r
extreme of the line continuum species can be classified which evolved under
density-independent conditions (r-strategists). r-strategists are short-lived
and display high reproductive potential. By contrast, K-strategists (species
classified closer to the K endpoint of the r-K gradient) evolved under densitydependent conditions, are long-lived and display low reproductive potential.
Strongly criticising the r-K selection model for its simplicity, Greenslade
(1972a,b), Southwood (1977, 1988) and Grime (1977, 1979) introduced habitattemplet models. More specifically, Grime and Greenslade added to the original
r-K line continuum a supplementary selection gradient termed "stress" or
"adversity selection", while Southwood stressed the significance of habitat structure as a templet for ecological strategies. Southwood et al. (1974) based upon
cost-benefit ideas originated the idea that the structural characteristics ofhabitat make up a templet against which evolutionary pressures fashion the ecological strategy of a species. This means that the selection of life history strategies
can be achieved only in terms of environmental variables (Korfiatis and Stamou,
submitted).
The novelty of habitat-templet models lies on the simultaneous consideration of physiological, behavioural, dispersal and demographic parameters
in connection with the basic properties of habitats (Korfiatis and Stamou,
submitted). Similar to the r-K selection model, habitat templets are graphic
models developed on qualitative grounds. The idea of using qualitative
models in ecology is ought to Levins (1968). Contrary to quantitative ones
accounting mainly for realism and precision, qualitative models account
more for realism and generality. Hence, the latter appear rich in biological
content and accordingly more informative (Haila 1986), describing more
complex phenomena.
Synthesis
Initiated by Cole (1954), strategic thinking in ecology resides upon the
concepts of allocation and strategy (Korfiatis and Stamou 1994). The corner
hypothesis underlying the development of schemata describing life history
strategies is rather simple: a limited amount of time and energy is available
throughout organisms' life. Hence, limited quantities should be invested in
various life cycle attributes in such a way as to achieve optimal adaptation of
organisms to environmental constraints. Obviously, the timing of life cycles
and the patterns of energy allocation drive the development of adaptive strategies, i.e. the development of those life history traits which maximise the
fitness of organisms. Thus, adaptive strategies are viewed as responses of
organisms to genetic and environmental constraints resulting in trade-offs
among life history characteristics.
The life history model most familiar to ecologists is that of r-K selection.
First introduced by MacArthur and Wilson in 1967, this model captured the
concept of life history strategies and overwhelmed strategic thinking until
the late 1970s. Pianka (1970) introduced the schema of the r-K line continuum on which species can be classified according to the number of produced
eggs and the survival of juveniles. According to model predictions, near the r
extreme of the line continuum species can be classified which evolved under
density-independent conditions (r-strategists). r-strategists are short-lived
and display high reproductive potential. By contrast, K-strategists (species
classified closer to the K endpoint of the r-K gradient) evolved under densitydependent conditions, are long-lived and display low reproductive potential.
Strongly criticising the r-K selection model for its simplicity, Greenslade
(1972a,b), Southwood (1977, 1988) and Grime (1977, 1979) introduced habitattemplet models. More specifically, Grime and Greenslade added to the original
r-K line continuum a supplementary selection gradient termed "stress" or
"adversity selection", while Southwood stressed the significance of habitat structure as a templet for ecological strategies. Southwood et al. (1974) based upon
cost-benefit ideas originated the idea that the structural characteristics ofhabitat make up a templet against which evolutionary pressures fashion the ecological strategy of a species. This means that the selection of life history strategies
can be achieved only in terms of environmental variables (Korfiatis and Stamou,
submitted).
The novelty of habitat-templet models lies on the simultaneous consideration of physiological, behavioural, dispersal and demographic parameters
in connection with the basic properties of habitats (Korfiatis and Stamou,
submitted). Similar to the r-K selection model, habitat templets are graphic
models developed on qualitative grounds. The idea of using qualitative
models in ecology is ought to Levins (1968). Contrary to quantitative ones
accounting mainly for realism and precision, qualitative models account
more for realism and generality. Hence, the latter appear rich in biological
content and accordingly more informative (Haila 1986), describing more
complex phenomena.