120
Synthesis
nean arthropods are cosmopolitans established prior to the Mediterranean
climate. Accordingly, this point concerns the adaptive value of the life history
traits of those cosmopolitan species which are able to adjust their life cycle
development to elements devising the severity of the Mediterranean habitats.
As shown in Chapter 3, Mediterranean arthropods are characterised by
rapid response to changing temperature regimes and low maintenance cost at
constant temperatures which, due to low QIO values, increases slightly with
increasing temperature. Due to a large temperature plateau, arthropods are
able to develop and reproduce over a large range of field temperatures in
spring and autumn. In winter Mediterranean arthropods can overcome low
temperatures for relatively long periods by entering quiscence and at the
same time are able to exploit instantaneous and random increases in temperature to accomplish part of their development. Moreover, metabolic activity of arthropods appears highly susceptible to high temperatures, and consequently high summer temperatures force most arthropods to aestivate,
entering an inactive stage. In conclusion, animals appear conservative with
respect to the short-term temperature pattern, and the moderately high
expenditure at fluctuating temperatures is counterbalanced by low energy
transformation capacity at constant temperatures, allowing for survival, further development and reproduction over a large array of temperature conditions. In contrast, summer aestivation and winter quiescence are conformist
elements forcing numbers of arthropods to follow the seasonal fluctuations
of the Mediterranean climate.
In an attempt to categorise the above characteristics, a classification scheme
involving two categories has been proposed. The first category includes conservative elements such as low metabolic activity, low QIO values, large range
of tolerance etc. allowing arthropods to survive and reproduce over large
ranges of variables. Apparently, elements in the conservative class relate to
the animals' endurance under the adverse Mediterranean conditions. The
second category includes conformist elements such as rapid response to
changing temperatures (accompanied by more efficient transformation of
energy), susceptibility to high temperatures, quiescence and aestivation
which force demographies to conform with the sesonality of the Mediterranean climate.
In many aspects, most Mediterranean arthropods appear to be demographic conservationists. Indeed, major demographic characteristics such as
mortality concentrated in immature instars, low or moderate mortality of
adults, slow development, brood protection, relatively long generation time,
and low to moderate reproductive values fit the K-selected attributes well.
The maintenance of populations showing a low rate of development and low
reproductive value involves a long adult life span. Moreover, precocity coupled
with limited body size and limited capability for energy storage leads to the
dispersal - to some extent - of reproductive effort over time. As was stressed
by Norton (1994), long adult life may entail costs invested in conservative ele-
Synthesis
nean arthropods are cosmopolitans established prior to the Mediterranean
climate. Accordingly, this point concerns the adaptive value of the life history
traits of those cosmopolitan species which are able to adjust their life cycle
development to elements devising the severity of the Mediterranean habitats.
As shown in Chapter 3, Mediterranean arthropods are characterised by
rapid response to changing temperature regimes and low maintenance cost at
constant temperatures which, due to low QIO values, increases slightly with
increasing temperature. Due to a large temperature plateau, arthropods are
able to develop and reproduce over a large range of field temperatures in
spring and autumn. In winter Mediterranean arthropods can overcome low
temperatures for relatively long periods by entering quiscence and at the
same time are able to exploit instantaneous and random increases in temperature to accomplish part of their development. Moreover, metabolic activity of arthropods appears highly susceptible to high temperatures, and consequently high summer temperatures force most arthropods to aestivate,
entering an inactive stage. In conclusion, animals appear conservative with
respect to the short-term temperature pattern, and the moderately high
expenditure at fluctuating temperatures is counterbalanced by low energy
transformation capacity at constant temperatures, allowing for survival, further development and reproduction over a large array of temperature conditions. In contrast, summer aestivation and winter quiescence are conformist
elements forcing numbers of arthropods to follow the seasonal fluctuations
of the Mediterranean climate.
In an attempt to categorise the above characteristics, a classification scheme
involving two categories has been proposed. The first category includes conservative elements such as low metabolic activity, low QIO values, large range
of tolerance etc. allowing arthropods to survive and reproduce over large
ranges of variables. Apparently, elements in the conservative class relate to
the animals' endurance under the adverse Mediterranean conditions. The
second category includes conformist elements such as rapid response to
changing temperatures (accompanied by more efficient transformation of
energy), susceptibility to high temperatures, quiescence and aestivation
which force demographies to conform with the sesonality of the Mediterranean climate.
In many aspects, most Mediterranean arthropods appear to be demographic conservationists. Indeed, major demographic characteristics such as
mortality concentrated in immature instars, low or moderate mortality of
adults, slow development, brood protection, relatively long generation time,
and low to moderate reproductive values fit the K-selected attributes well.
The maintenance of populations showing a low rate of development and low
reproductive value involves a long adult life span. Moreover, precocity coupled
with limited body size and limited capability for energy storage leads to the
dispersal - to some extent - of reproductive effort over time. As was stressed
by Norton (1994), long adult life may entail costs invested in conservative ele-