The Joint Effect of Temperature and Humidity on Feeding Activity and Demography
53
tion is the assimilation coefficient recorded in G. balcanica which is higher
than that estimated for desert (Wooten and Crawford 1975) or temperate
counterparts (Mason 1970). Unfortunately, no relevant data for other Mediterranean arthropods exist, but it may generally hold true that low maintenance cost of arthropods is coupled with efficient exploitation of food
resources.
4.5.3
Long-Term Effect ofTemperature
The long-term effect of temperature is mainly impressed on demographic
parameters. Hence, demographic responses to changing temperatures are the
main determinants of life history strategies in Mediterranean arthropods. So
far, life history schedules have been reported for arthropods from ephemeral,
constant or adverse habitats, and relevant tables depicting r, K and A life
history categories have been compiled. Life histories of arthropods from seasonal environments hardly fit such patterns. It is expected that strongly fluctuating temperature and humidity regimes in combination with intensive
exploitation of the land lead to the development of specific life history schedules compatible with the specificity of the Mediterranean environment. More
specifically, demographic characteristics such as the timing of egg deposition, duration of larval development, and arrest in life cycle development
(e.g. quiescence, aestivation), allowing for the synchronisation of phenologies with seasonally varying temperature and humidity are of great importance.
To describe life history correlates in response to changing temperature,
extrapolation of laboratory data is needed along with actual field data. Successful rearing of most arthropods in the laboratory is possible at temperatures above a certain threshold. For example, oribatids and collembolans
from Hortiatis were successfully cultured at temperatures beyond 19 DC (Asikidis 1989; Argyropoulou, unpublished). At intermediate temperatures of
15-17 DC the life cycle development of most species was completed, although
no egg deposition were recorded. Below 12 DC no oviposistion and no development into later stadia were recorded, while the animals hardly moved. At
temperatures below 5 DC, no mortality was recorded and the animals remained in quiescence preserving their ability to respond immediately to subsequent rising temperature. Early instars develop more slowly at all temperatures than later ones, while intermediate stadia, e.g. protonymphs and deutonymphs of oribatids, develop even faster (the quadratic effect is highly significant; Fig.4.lO). The rate oflarval development increases from 17 to 23 DC
and decreases slightly in the transition range of 23-27 DC.
Higher mortality of earlier life stages is frequently reported for arthropods
of Mediterranean provenance (e.g. Warburg et al. 1984; Bercovitz and Warburg 1985; Crawford et al. 1987; Matthiessen and Ridsdill-Smith 1991) and is
53
tion is the assimilation coefficient recorded in G. balcanica which is higher
than that estimated for desert (Wooten and Crawford 1975) or temperate
counterparts (Mason 1970). Unfortunately, no relevant data for other Mediterranean arthropods exist, but it may generally hold true that low maintenance cost of arthropods is coupled with efficient exploitation of food
resources.
4.5.3
Long-Term Effect ofTemperature
The long-term effect of temperature is mainly impressed on demographic
parameters. Hence, demographic responses to changing temperatures are the
main determinants of life history strategies in Mediterranean arthropods. So
far, life history schedules have been reported for arthropods from ephemeral,
constant or adverse habitats, and relevant tables depicting r, K and A life
history categories have been compiled. Life histories of arthropods from seasonal environments hardly fit such patterns. It is expected that strongly fluctuating temperature and humidity regimes in combination with intensive
exploitation of the land lead to the development of specific life history schedules compatible with the specificity of the Mediterranean environment. More
specifically, demographic characteristics such as the timing of egg deposition, duration of larval development, and arrest in life cycle development
(e.g. quiescence, aestivation), allowing for the synchronisation of phenologies with seasonally varying temperature and humidity are of great importance.
To describe life history correlates in response to changing temperature,
extrapolation of laboratory data is needed along with actual field data. Successful rearing of most arthropods in the laboratory is possible at temperatures above a certain threshold. For example, oribatids and collembolans
from Hortiatis were successfully cultured at temperatures beyond 19 DC (Asikidis 1989; Argyropoulou, unpublished). At intermediate temperatures of
15-17 DC the life cycle development of most species was completed, although
no egg deposition were recorded. Below 12 DC no oviposistion and no development into later stadia were recorded, while the animals hardly moved. At
temperatures below 5 DC, no mortality was recorded and the animals remained in quiescence preserving their ability to respond immediately to subsequent rising temperature. Early instars develop more slowly at all temperatures than later ones, while intermediate stadia, e.g. protonymphs and deutonymphs of oribatids, develop even faster (the quadratic effect is highly significant; Fig.4.lO). The rate oflarval development increases from 17 to 23 DC
and decreases slightly in the transition range of 23-27 DC.
Higher mortality of earlier life stages is frequently reported for arthropods
of Mediterranean provenance (e.g. Warburg et al. 1984; Bercovitz and Warburg 1985; Crawford et al. 1987; Matthiessen and Ridsdill-Smith 1991) and is