Spatial Patterns
97
beginning of the dry period some individuals move to the deeper layer to lay
eggs. In the same vane, Ghabbour (1983) stated that most isopods in Egyptian habitats burrow to escape intensive heat and drought. He reported that
individuals of Porcellio olivieri retreat to a depth of 10 to 25 cm. Paris offered
an analogous explanation (1963) with respect to the spatial distribution of
the isopod Armadillidium vulgare. In summer animals move downwards to
soil as deep as 45 cm to avoid drought, while horizontal movement to moist
microsites also offers refuge against drought. Animals emerge from their
refuges at night to feed.
Vertical movements of epiphytic arthropods are related directly to climatic
variables such as air temperature and relative humidity. For example, vertical
movements of Araneae probably associated with seasonal changes in climatic
variables were seen in bushes (Paraschi 1988). During summer in a xeric
Greek ecosystem, most epiphytic Araneae were confined to a height below 70
cm, while during the wet period greater numbers were recorded within a
range of 70-140 cm above the ground.
The above explanations link vertical migration directly to environmental
conditions. Iatrou and Stamou (1991) correlated vertical distribution of the
diplopod Glomeris balcanica with its foraging activity conditioned by the
water content of the litter. In the wet Mediterranean formation on Hortiatis,
G. balcanica is confined almost exclusively to the humus layer for most of the
year, while during periods of highest feeding activity - from the middle of
October to the end of November and again from the middle of March to the
end of April - numbers are evenly distributed among the litter and humus
layers.
7.3.2
Horizontal Distribution
The horizontal distribution pattern of most arthropod groups, such as pseudoscorpions, spiders and bristle tails, varies seasonally (Magioris and Tsiourlis
1992). In general, small-scale horizontal patterns are associated either with
intraspecifc relationships or with the distribution of sites for egg laying and
sites of food resources, while large-scale patterns result from vectorial climatic, landscape and anthropogenic factors.
Vectorial factors condition habitat use by scorpions (Warburg et al. 1980).
Scorpio maurus fuscus with its low potential for water regulation inhabits
areas of high precipitation, dense vegetation and deep soil which provide
suitable conditions for maintaining water and thermal balance in the deeper
soil layers. By contrast, the efficient conserver of water, Buthotus judaicus,
which is unable to dig borrows, is more abundant in rocky habitats which
provide it with suitable microclimatic refuges.
Crawford et al. (1987) interpreted the prolonged dry-season foraging of
Archispirostreptus tumuliporus. judaicus in the immediate vicinity of shel-
97
beginning of the dry period some individuals move to the deeper layer to lay
eggs. In the same vane, Ghabbour (1983) stated that most isopods in Egyptian habitats burrow to escape intensive heat and drought. He reported that
individuals of Porcellio olivieri retreat to a depth of 10 to 25 cm. Paris offered
an analogous explanation (1963) with respect to the spatial distribution of
the isopod Armadillidium vulgare. In summer animals move downwards to
soil as deep as 45 cm to avoid drought, while horizontal movement to moist
microsites also offers refuge against drought. Animals emerge from their
refuges at night to feed.
Vertical movements of epiphytic arthropods are related directly to climatic
variables such as air temperature and relative humidity. For example, vertical
movements of Araneae probably associated with seasonal changes in climatic
variables were seen in bushes (Paraschi 1988). During summer in a xeric
Greek ecosystem, most epiphytic Araneae were confined to a height below 70
cm, while during the wet period greater numbers were recorded within a
range of 70-140 cm above the ground.
The above explanations link vertical migration directly to environmental
conditions. Iatrou and Stamou (1991) correlated vertical distribution of the
diplopod Glomeris balcanica with its foraging activity conditioned by the
water content of the litter. In the wet Mediterranean formation on Hortiatis,
G. balcanica is confined almost exclusively to the humus layer for most of the
year, while during periods of highest feeding activity - from the middle of
October to the end of November and again from the middle of March to the
end of April - numbers are evenly distributed among the litter and humus
layers.
7.3.2
Horizontal Distribution
The horizontal distribution pattern of most arthropod groups, such as pseudoscorpions, spiders and bristle tails, varies seasonally (Magioris and Tsiourlis
1992). In general, small-scale horizontal patterns are associated either with
intraspecifc relationships or with the distribution of sites for egg laying and
sites of food resources, while large-scale patterns result from vectorial climatic, landscape and anthropogenic factors.
Vectorial factors condition habitat use by scorpions (Warburg et al. 1980).
Scorpio maurus fuscus with its low potential for water regulation inhabits
areas of high precipitation, dense vegetation and deep soil which provide
suitable conditions for maintaining water and thermal balance in the deeper
soil layers. By contrast, the efficient conserver of water, Buthotus judaicus,
which is unable to dig borrows, is more abundant in rocky habitats which
provide it with suitable microclimatic refuges.
Crawford et al. (1987) interpreted the prolonged dry-season foraging of
Archispirostreptus tumuliporus. judaicus in the immediate vicinity of shel-