Synchronisation Tactics
69
ods of modest moisture. Warburg et al. (1984) report that in isopods from
more xeric habitats, reproduction and further oscillations in population
numbers are related mostly to air humidity and rain. By contrast, in mesic
habitats temperature is the factor modulating the duration of oocyte development and the onset and duration of egg laying. Moreover, unlike millipedes from more xeric habitats where moisture is the prevailing factor, temperature conditions are of greater importance for egg laying G. balcanica inhabiting a subhumid habitat. Under milder moisture conditions recruitment is
conditioned by temperatures having prevailed in the organic layers of the soil
during egg synthesis 8 months earlier. The onset as well as duration of egg
deposition are strongly dependent on moderate temperatures varying from 7
to 25°C (Iatrou and Stamou 1989b). In addition, unlike the instars of their
relatives in more arid regions, egg hatching and emergence of the first free
ins tars from the egg capsules or marsupium of Mediterranean arthropods are
temperature rather than moisture dependent (e.g. Crawford et al. 1987). In
any case, egg synthesis, oviposition and hatching in Mediterranean regions
occur during brief periods, thereby contributing to synchronisation of life
cycles with the seasonally or interannually varying environment. (Fig. 5.4).
5.2
Synchronisation Tactics
Environmental thresholds, in conjunction with age at maturity and voltinism
are of crucial importance for the synchronisation of arthropod activity
(recruitment to population, interruptions in life cycle development etc.) with
the fluctuating environment. Univoltine species with obligatory diapause
and/or dormancy, and bivoltine species with facultative aestivation and dormancy ensure synchronisation of the life cycle of epiphytic arthropods with
seasonally varying climatic variables.
Voltinism is also important for synchronisation in soil-dwelling arthropods. According to Siepel (1994), it can be stated that high reproductive success and circumscribed oviposition accompanied by winter quiescence
and/or aestivation are the principal correlates of seasonal rhythms in Mediterranean regions. Circumscribed oviposition and facultative aestivation or
quiescence enable animals to easily overcome unfavourable periods of the
seasonal cycle.
Most soil inhabitants carry their eggs for long periods and can lay them
opportunistically whenever environmental conditions are temporarily within favourable limits. Thus, circumscribed field oviposition, which is beneficial
in seasonally varying environments, is the by-product of environmentally
conditioned schedules of oviposition. Moreover, true diapause or dormancy
involving morphological and physiological changes are uncommon in soil
arthropods, and only a few collembolan species enter ecomorphosis or any-
69
ods of modest moisture. Warburg et al. (1984) report that in isopods from
more xeric habitats, reproduction and further oscillations in population
numbers are related mostly to air humidity and rain. By contrast, in mesic
habitats temperature is the factor modulating the duration of oocyte development and the onset and duration of egg laying. Moreover, unlike millipedes from more xeric habitats where moisture is the prevailing factor, temperature conditions are of greater importance for egg laying G. balcanica inhabiting a subhumid habitat. Under milder moisture conditions recruitment is
conditioned by temperatures having prevailed in the organic layers of the soil
during egg synthesis 8 months earlier. The onset as well as duration of egg
deposition are strongly dependent on moderate temperatures varying from 7
to 25°C (Iatrou and Stamou 1989b). In addition, unlike the instars of their
relatives in more arid regions, egg hatching and emergence of the first free
ins tars from the egg capsules or marsupium of Mediterranean arthropods are
temperature rather than moisture dependent (e.g. Crawford et al. 1987). In
any case, egg synthesis, oviposition and hatching in Mediterranean regions
occur during brief periods, thereby contributing to synchronisation of life
cycles with the seasonally or interannually varying environment. (Fig. 5.4).
5.2
Synchronisation Tactics
Environmental thresholds, in conjunction with age at maturity and voltinism
are of crucial importance for the synchronisation of arthropod activity
(recruitment to population, interruptions in life cycle development etc.) with
the fluctuating environment. Univoltine species with obligatory diapause
and/or dormancy, and bivoltine species with facultative aestivation and dormancy ensure synchronisation of the life cycle of epiphytic arthropods with
seasonally varying climatic variables.
Voltinism is also important for synchronisation in soil-dwelling arthropods. According to Siepel (1994), it can be stated that high reproductive success and circumscribed oviposition accompanied by winter quiescence
and/or aestivation are the principal correlates of seasonal rhythms in Mediterranean regions. Circumscribed oviposition and facultative aestivation or
quiescence enable animals to easily overcome unfavourable periods of the
seasonal cycle.
Most soil inhabitants carry their eggs for long periods and can lay them
opportunistically whenever environmental conditions are temporarily within favourable limits. Thus, circumscribed field oviposition, which is beneficial
in seasonally varying environments, is the by-product of environmentally
conditioned schedules of oviposition. Moreover, true diapause or dormancy
involving morphological and physiological changes are uncommon in soil
arthropods, and only a few collembolan species enter ecomorphosis or any-