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62 | III. Biotope and animal associations
biotope and, if these conditions include elements of the biocoenosis, as
correctly mentioned by Schwenke, there is no reason that we drop the dualism
of biotope and biocoenosis; it is only a serious warning that we should not
seek support in biocoenosis when trying to define the biotope. It is certain
that underlying the biocoenosis, there is a hidden categorical factor that
determines its creation and composition. Schwenke himself is obliged to use
the term “biotope” later in his work, indicating that the two terms are not
identical, and neither can be abandoned. No one can deny the existence of
deep differences among the biocoenoses of a sandy grassland, a calcareous
mountain, and the alpine region of a granite mountain, and, if we were to
declare that these places are different because of the differences in their animal
associations, we would commit the logical error of idem per idem.
What, therefore, can be considered a biotope? The biotope is a space that
is suitable for the formation of a biocoenosis because, potentially, it has the
energy sources necessary for its existence (Hesse, 1924; Dudich, 1939; Nagy,
1944).
In the biosphere, defined as the aquatic and terrestrial space suitable for
life, innumerable biotopes can be distinguished. The condition that a biotope
is a spatial unit suitable for the formation of a biocoenosis, unequivocally
indicates a lower limit; the minimum necessary space to include a whole
biocoenosis. The term biotope cannot indicate a smaller spatial unit than
this.
The biotope is exposed to cosmic (e.g. radiation from the sun) and
meteorological (precipitation, temperature, wind) factors which, themselves,
can transform a space originally unsuitable for life, into one that can become
a biotope. From this, it also follows that, at present, biotopes exist without
life. A fresh lava flow, for example, is not suitable for animal or plant life, not
only when hot but, for a while, even after cooled down and solidified;
ultimately, atmospheric forces complete the chemical transformation that
enables plant life to start and, by transforming the sun's energy, plants allow
the formation of animal associations. The settlement of the first pioneers,
however, depends on chance (consider the rock emerging from the sea) and,
until this chance event occurs, the area in question can be equivalent to other
biotopes, the only difference being the lack of life.
The first settlers of this “space-turned-into-new-biotope” are, by necessity,
representatives of the plant kingdom. How a rock face, seemingly unsuitable
to support life, turns into a biotope is nicely illustrated by Falger’s studies
(1914, 1922-23), according to which the first bacteria, algae and fungi are
followed by the first animals; rhizopodes, ciliates, rotifers and nematodes.
The next step is the settling of lichens and mosses and, at the same time,
humus-forming animals also appear. Oosting and Anderson (1939), also
studying the development of plant cover on rocky substrate, found regular,
concentric zonation, the centre of which was always occupied by the most
advanced association, while the hardiest pioneers were found at the periphery.