72
2000
Life Cycle Tactics and Development
62
NDJ FMAMJ JASOND
Time (months)
Fig. 5.5. Population dynamics of the oribatid S. cf latipes. The model proposed by Stamou
(1986a) is fitted on census data. For the sake of simplicity only theoretical values are depicted)
the original data. The conclusions drawn from evaluating the model's parameters (Stamou and Sgardelis 1989) are as follows: although a preponderance
of mature individuals was recorded throughout the year, adults are most
numerous in late autumn and early winter, and the peak in density occurs in
November/December. As in most oribatids from temperate regions (Luxton
1981b), the adult is the overwintering stage on Hortiatis. S. cf.latipes is univoltine, initiating one generation per year. Eggs develop and are laid soon
after the animals attain maturity. The greatest numbers of eggs are to be
found in the abdomens of females in March, while the oviposition period
lasts from February to June. New larvae first emerge in April, and during
summer the immature forms develop rapidly into subsequent life stages. As
shown in the model, adults appear to be precocious, and reproductive effort
is distributed over a short period of time. These two features are typical of
populations inhabiting seasonal environments. Furthermore, the development of juvenile instars follows the seasonality of the environment. They
develop during short specific periods, while the overall life cycle shows
annual periodicity.
Pilogalumna allifera and Achipteria oudemansi, the other characteristic
species, share the above characteristics of S. cf. latipes. However, their life
cycles follow a different timing. The eggs withstand summer drought by
remaining dormant and hatch in early autumn. Juveniles develop rapidly in
the autumn and adults emerge in early winter. Moreover, P. aUifera lays eggs
in open sites and appears seasonally iteroparus, ovipositing twice a year, i.e.
in early spring and in autumn. Autumnal eggs overwinter and develop along
with those laid in the following spring. Thus, seasonal iteroparity spreads the
risk of abiotically unpredictable disasters in exposed sites, since even the
complete loss of a reproductive season is allowed.
2000
Life Cycle Tactics and Development
62
NDJ FMAMJ JASOND
Time (months)
Fig. 5.5. Population dynamics of the oribatid S. cf latipes. The model proposed by Stamou
(1986a) is fitted on census data. For the sake of simplicity only theoretical values are depicted)
the original data. The conclusions drawn from evaluating the model's parameters (Stamou and Sgardelis 1989) are as follows: although a preponderance
of mature individuals was recorded throughout the year, adults are most
numerous in late autumn and early winter, and the peak in density occurs in
November/December. As in most oribatids from temperate regions (Luxton
1981b), the adult is the overwintering stage on Hortiatis. S. cf.latipes is univoltine, initiating one generation per year. Eggs develop and are laid soon
after the animals attain maturity. The greatest numbers of eggs are to be
found in the abdomens of females in March, while the oviposition period
lasts from February to June. New larvae first emerge in April, and during
summer the immature forms develop rapidly into subsequent life stages. As
shown in the model, adults appear to be precocious, and reproductive effort
is distributed over a short period of time. These two features are typical of
populations inhabiting seasonal environments. Furthermore, the development of juvenile instars follows the seasonality of the environment. They
develop during short specific periods, while the overall life cycle shows
annual periodicity.
Pilogalumna allifera and Achipteria oudemansi, the other characteristic
species, share the above characteristics of S. cf. latipes. However, their life
cycles follow a different timing. The eggs withstand summer drought by
remaining dormant and hatch in early autumn. Juveniles develop rapidly in
the autumn and adults emerge in early winter. Moreover, P. aUifera lays eggs
in open sites and appears seasonally iteroparus, ovipositing twice a year, i.e.
in early spring and in autumn. Autumnal eggs overwinter and develop along
with those laid in the following spring. Thus, seasonal iteroparity spreads the
risk of abiotically unpredictable disasters in exposed sites, since even the
complete loss of a reproductive season is allowed.