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I NSULARLIKE A CCELERATED S PECIATION IN O CTODRILUS IN THE C ARPATHIANS
The large number of endemic Octodrilus species distributed in patches in small areas of the
Carpathians, as well as in the Alps and Dinara Mountains, could be explained by a process of
insularlike speciation (Pop et al. 1994). The following conditions are considered to favor accelerated
insularlike speciation:
Stenobiontism (species that tolerate only narrow variations of environmental factors) regard-
ing mountain habitats on Mesozoic limestone
Insularity of these habitats, leading to geographical and reproductive isolation
The size of populations, which is an essential factor because most of the isolated Octodrilus
populations are rather small, thus enhancing the probability of quick genetic changes
Low dispersal ability because earthworms are almost sedentary forms
The occurrence of parthenogenesis, indicated by indirect morphologic features; this kind of
reproductive isolation might also be an accelerating factor for species segregation because
a mutation is more easily preserved and spread within a population in the absence of
genetic recombinations through biparentalism
The Apuseni Mountains are seemingly one of the most prolific speciation centers of the genus.
Timing of the Alpino-Carpathian orogenesis (i.e., raising of the mountains) and phytohistorical
data support the idea that endemic Octodrilus species were able to survive the Pleistocene glacia-
tions in Carpathian refuges. Distinct Octodrilus lines are found in the limestone areas of the
Carpathians, the Alps, and the Dinara Mountains.
ECOLOGY OF THE GENUS OCTODRILUS
E ARTHWORM C OMMUNITIES D OMINATED BY O CTODRILUS S PECIES
As discussed in the section on variability of characters, two groups of Octodrilus species could
be distinguished: a group of widely distributed, usually acid-tolerant, medium-size species and
a group of endemic species, usually calcophilous or confined to limestone areas, that are
medium-size to very large species of earthworms (Pop 1985, 1997). The great majority of the
Octodrilus species were recorded in the vegetation belts of beech or beech-hornbeam forests
and more rarely in mixed beech spruce-fir forests, as well as in corresponding grasslands (Pop
1982). Beech ( F. sylvatica ) is the main forest tree in Romania, occurring on both aspects of
the Carpathians and forming a distinct vegetation belt, both as mixed beech-spruce-fir or beech-
hornbeam forests. The obvious individuality of Carpathian beech forests justifies their placement
in an independent phytosociological alliance, namely, Symphyto cordato-Fagetum Vida 59,
Fagion dacicum So– 62. The earthworm fauna of the Carpathian beech forests differs corre-
spondingly from that of similar biotopes in the Alps or Dinara Mountains. In this forest biotope
are found the majority of Carpathian endemic species and, as a particular feature, some of the
largest lumbricids known.
The earthworm communities (Pop 1997), previously referred to as synusia (Pop 1982, 1985,
1987), comprise two main structural patterns related to the nature of the substrata (igneous-
crystalline vs. limestone-dolomite rocks), which in turn reflects peculiarities of the soils and, within
certain limits, some features of the phytocenoses.
The structural pattern of these earthworm communities is maintained by a substitution process
of the ecologically similar species, which are as a rule vicariants, that is, they do not occur together
in the same place. This substitution process was found mainly at the level of the same ecologic
categories, namely, epigeic species (surface living), endogeic species (living in the depth of soil),
and anecic species (vertical migratory) species. Their ratios are related closely to soil properties
 
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