Life History Characteristics
65
5.1.3.2
Semelparity and Iteroparity
The great majority of adult Mediterranean arthropods lay their eggs early in
their development. For example, the oribatid Scheloribates cf latipes with
more than 1 year of adult life lays its first eggs 7 weeks after reaching adulthood. The millipede A. t. judaicus from mesic habitats, which has a life span
of 11 years, also deposits eggs 4 months after reaching adulthood.
As to reproductive patterns, Warburg et al. (1993) report that most of the
isopods from Israel are iteroparus, and only two local species, a desert and a
Mediterranean one, are semelparus. Moreover, different isopod species inhabiting the same habitat differ in their reproductive patterns (Warburg
1992), and these differences are associated with anatomical differences in the
ovaries (Warburg 1994). S. tiberianum is short lived, breeds in spring, and is
semelparus, realising a considerable number of mancas before dying, whereas A. officinalis can survive for 9 years (or probably more), breeds in the fall,
and is iteroparus. It seems that in isopods semelparity and iteroparity are
equally successful reproductive strategies in the Mediterranean regions of
Israel.
Iteroparity is generally considered to be the most economic reproductive
strategy, since specific morphological adaptations such as physogasty or
swelling of the abdomen, high energy expenditure in short periods (affecting
survival), as well as extra overwintering or oversummering adaptations are
needless (Siepel 1994). According to Warburg (1987a), in variable environments such as the Mediterranean ones iteroparity is favoured whenever the
probability of adult survival is greater than that of juveniles.
In general, Mediterranean arthropods show traits such as concentrated
mortality of immature individuals, limited body size, low metabolic rate, and
a relatively long adult life span, which characterises iteroparus species.
Nonetheless, it seems probable that climatic predictability may outweigh disadvantages related to temporal uncertainties, and deviation from iteroparity
to circumscribed oviposition is favoured. Thus, notwithstanding the above
characteristics, compromising patterns are favoured in Mediterranean
regions. Most arthropods appear precocious and the main bulk of eggs is
deposited during brief periods of time, while a slight distribution of reproductive effort upon different adult age groups also occurs. Deviations from
iteroparity do not even increase energy costs. In fact, due to low QIO values
and efficient thermoregulation over the optimal temperature range, Mediterranean arthropods may significantly reduce the energy cost of reproduction.
The phenomenon of egg laying in Mediterranean arthropods is well exemplified by three oribatid and two collembolan species from Hortiatis
(Figs. 5.2, 5.3). In all cases the animals deposit their eggs soon after reaching
65
5.1.3.2
Semelparity and Iteroparity
The great majority of adult Mediterranean arthropods lay their eggs early in
their development. For example, the oribatid Scheloribates cf latipes with
more than 1 year of adult life lays its first eggs 7 weeks after reaching adulthood. The millipede A. t. judaicus from mesic habitats, which has a life span
of 11 years, also deposits eggs 4 months after reaching adulthood.
As to reproductive patterns, Warburg et al. (1993) report that most of the
isopods from Israel are iteroparus, and only two local species, a desert and a
Mediterranean one, are semelparus. Moreover, different isopod species inhabiting the same habitat differ in their reproductive patterns (Warburg
1992), and these differences are associated with anatomical differences in the
ovaries (Warburg 1994). S. tiberianum is short lived, breeds in spring, and is
semelparus, realising a considerable number of mancas before dying, whereas A. officinalis can survive for 9 years (or probably more), breeds in the fall,
and is iteroparus. It seems that in isopods semelparity and iteroparity are
equally successful reproductive strategies in the Mediterranean regions of
Israel.
Iteroparity is generally considered to be the most economic reproductive
strategy, since specific morphological adaptations such as physogasty or
swelling of the abdomen, high energy expenditure in short periods (affecting
survival), as well as extra overwintering or oversummering adaptations are
needless (Siepel 1994). According to Warburg (1987a), in variable environments such as the Mediterranean ones iteroparity is favoured whenever the
probability of adult survival is greater than that of juveniles.
In general, Mediterranean arthropods show traits such as concentrated
mortality of immature individuals, limited body size, low metabolic rate, and
a relatively long adult life span, which characterises iteroparus species.
Nonetheless, it seems probable that climatic predictability may outweigh disadvantages related to temporal uncertainties, and deviation from iteroparity
to circumscribed oviposition is favoured. Thus, notwithstanding the above
characteristics, compromising patterns are favoured in Mediterranean
regions. Most arthropods appear precocious and the main bulk of eggs is
deposited during brief periods of time, while a slight distribution of reproductive effort upon different adult age groups also occurs. Deviations from
iteroparity do not even increase energy costs. In fact, due to low QIO values
and efficient thermoregulation over the optimal temperature range, Mediterranean arthropods may significantly reduce the energy cost of reproduction.
The phenomenon of egg laying in Mediterranean arthropods is well exemplified by three oribatid and two collembolan species from Hortiatis
(Figs. 5.2, 5.3). In all cases the animals deposit their eggs soon after reaching