92
Community Structure
Di Castri (1973) as well as Di Castri and Vitali-Di Castri (1981) reported
values of species diversity intermediate between those of rain forests on the
one hand and desert or antarctic habitats on the other. Di Castri (1973) also
stated that the average density of arthropods in Mediterranean-type ecosystems is intermediate between the values of moderate and severe environments. Field data seem to corroborate the above suggestions. For example,
Postle (1985) reported arthropod densities in the range of 13700-39400 and
1300-34000 individuals m- 2 in the soil and litter of an Australian jarrah forest,
respectively, while Sgardelis and Margaris (1993) recorded about 49 000 surface and soil arthropods m- 1 in a Greek phrygana. The above values, as well as
many others, lie towards the center of histograms depicting arthropod densities in a variety of ecosystems (Petersen and Luxton 1982).
It is worth noting that within Mediterranean-type ecosystems, both numbers of individuals and species diversity generally decrease along the humidxeric and natural-anthropogenic gradients (Bigot and Bodot 1973; Di Castri
1973; Karamaouna 1990). For instance, the characteristics of the composition
of macroarthropod populations from a degraded evergreensclerophyllous
system and a neighbouring phryganic one do not differ. Significantly lower
numbers have been recorded in the latter and attributed to differences in primary production and the number of outcropping stones (Maggioris 1985).
However, the species diversity of isopod communities in xeric habitats of
Israel is higher than that estimated for more xeric Egyptian environments,
but the opposite has also been cited. Warburg et al. (1978) recorded higher
numbers of isopod species in rather xeric than in rather humid habitats of
northern Israel.
In general, Acari - especially oribatid mites - dominate numerically
among arthropods, while Collembola is the second most important group.
Acari, followed by Collembola, are frequently also the most diverse groups
(Postle et al. 1991). The ratios of oribatids to collembolan and of oribatids to
prostigmatids have sometimes been used for rough characterisation of the
physiognomy of the mesofauna in terrestrial ecosystems. The values of both
ratios in Mediterranean ecosystems (Sgardelis et al. 1981) are lower than
those reported for more xeric habitats (Wallwork 1972), while they are comparable with values reported for deciduous forests (e.g. Lebrun 1971).
Spiders and diplopods, followed by Coleoptera, are usually the most abundant surface and soil macroarthropods (Di Castri and Vitali-Di Castri 1981;
Sgardelis and Margaris 1983,1993; Karamaouna 1990). Moreover, there is evidence that within taxonomic groups only a few species dominate communities. For example, in a Greek insular ecosystem Trihas and Legakis (1991)
reported that only two species, namely Carter us calydonious and Acinopus
subquadratus, are by far the most dominant among Carabidae. Again, when
studying isopods from mesic and xeric habitats in northern Israel, Warburg
et al. (1984) found 15 species to be present, although the community was
dominated by only two, namely Metoponorthus pruinosus and Philoscia mus-
Community Structure
Di Castri (1973) as well as Di Castri and Vitali-Di Castri (1981) reported
values of species diversity intermediate between those of rain forests on the
one hand and desert or antarctic habitats on the other. Di Castri (1973) also
stated that the average density of arthropods in Mediterranean-type ecosystems is intermediate between the values of moderate and severe environments. Field data seem to corroborate the above suggestions. For example,
Postle (1985) reported arthropod densities in the range of 13700-39400 and
1300-34000 individuals m- 2 in the soil and litter of an Australian jarrah forest,
respectively, while Sgardelis and Margaris (1993) recorded about 49 000 surface and soil arthropods m- 1 in a Greek phrygana. The above values, as well as
many others, lie towards the center of histograms depicting arthropod densities in a variety of ecosystems (Petersen and Luxton 1982).
It is worth noting that within Mediterranean-type ecosystems, both numbers of individuals and species diversity generally decrease along the humidxeric and natural-anthropogenic gradients (Bigot and Bodot 1973; Di Castri
1973; Karamaouna 1990). For instance, the characteristics of the composition
of macroarthropod populations from a degraded evergreensclerophyllous
system and a neighbouring phryganic one do not differ. Significantly lower
numbers have been recorded in the latter and attributed to differences in primary production and the number of outcropping stones (Maggioris 1985).
However, the species diversity of isopod communities in xeric habitats of
Israel is higher than that estimated for more xeric Egyptian environments,
but the opposite has also been cited. Warburg et al. (1978) recorded higher
numbers of isopod species in rather xeric than in rather humid habitats of
northern Israel.
In general, Acari - especially oribatid mites - dominate numerically
among arthropods, while Collembola is the second most important group.
Acari, followed by Collembola, are frequently also the most diverse groups
(Postle et al. 1991). The ratios of oribatids to collembolan and of oribatids to
prostigmatids have sometimes been used for rough characterisation of the
physiognomy of the mesofauna in terrestrial ecosystems. The values of both
ratios in Mediterranean ecosystems (Sgardelis et al. 1981) are lower than
those reported for more xeric habitats (Wallwork 1972), while they are comparable with values reported for deciduous forests (e.g. Lebrun 1971).
Spiders and diplopods, followed by Coleoptera, are usually the most abundant surface and soil macroarthropods (Di Castri and Vitali-Di Castri 1981;
Sgardelis and Margaris 1983,1993; Karamaouna 1990). Moreover, there is evidence that within taxonomic groups only a few species dominate communities. For example, in a Greek insular ecosystem Trihas and Legakis (1991)
reported that only two species, namely Carter us calydonious and Acinopus
subquadratus, are by far the most dominant among Carabidae. Again, when
studying isopods from mesic and xeric habitats in northern Israel, Warburg
et al. (1984) found 15 species to be present, although the community was
dominated by only two, namely Metoponorthus pruinosus and Philoscia mus-