4
Dynamic Zoogeography
In zoogeography, as weIl as evolution, there is a continuous flow of changes,
but in the short human perspective only a small time-glimpse of the major unfolding can be witnessed. Zoogeography is in a better situation than some of the
related historico-evolutionary sciences: we are the witnesses of a major unsettling
of the animal distribution owing to the Pleistocene glaciations. In the present
period we are living through a warm interglacial with fauna gradually spreading
back over the ice- and frost-damaged areas. Lindroth (1956) has described many
cases of northward spread of animals into presently ice-free Scandinavia. According to Udvardy (1969, p.150): "Temperate and subpolar ecosystems were depleted
by the recent, drastic glaciations, and have only recently begun their renewed
evolution". This statement is true not only for the terrestrial fauna; a depletion
and destruction ofbiota also occurred in the sea.
Whereas in the open oceans the Pleistocene fluctuations caused mere advances and retreats, narrowing or widening of area, the situation was different in
the inner, mediterranean basins such as the Mediterranean and Red Seas. Here
the changes had zoogeographically defmed dimensions: whole series of species
disappeared from a given marine basin and at present are gradually returning.
Many data on this fluctuating dynamism of the Pleistocene mediterranean
biota can be found in Segerstrale (1957), Mars (1963), Peres (1967), Pusanov
(1967), and Por (1975a). These are slow decennial advances oflittoral species from
the straits connecting with the open ocean inward into the mediterranean. For
fish or plankton these are spotlike appearances of reproducing or metamorphosing swarms within sterile or larval populations that enter the sea (Fig.1).
In the mediterranean seas, depleted by Pleistocene temperature and salinity
fluctuations, the resettling process is perhaps even more marked than in the
terrestrial habitats. Repopulation proceeds only through the narrow Gibraltar or
Bosphorus Straits and the gradient of advance is very near to linear. On the other
hand, the far end of the mediterranean is a hermetically closed depauperation
area, a cul de sac comparable only to such areas as the southern tip of South
America (Darlington, 1959). In these marine cul de sacs-like the farthest Eastern
Mediterranean or the Gulf of Bothnia-the influence of the most extremely expressed environmental fluctuation is complemented by a "distance and time barrier" (Udvardy, 1969). The period of the Pleistocene fluctuation was in this case
too short for the decennially spreading species to reach the far end of the Mediterranean.
The fact that the Eastern Mediterranean and the Gulf of Suez of the Red Sea
are cul de sacs oftwo mediterranean seas had, and still has a decisive influence on
the quality and direction of the faunal interchange through the Suez Canal. This
has already been emphasized by Ben-Tuvia (1966) and Por (1971 b) and will
recurrently be discussed in the following chapters.
The above-mentioned postglacial (or interglacial) faunal adjustments are
small-step changes in which isolated species only are involved. Following Dansereau (1957) and Bänärescu and Bo~caiu (1973), the zoogeography should study the
repartition and dynamics of whole communities and ecosystems, of "syntaxons"
in their words. De Lattin (1967) also discussed Pleistocene movements in terms of
relative, often antagonistic, movements of three basic terrestrial types of ecosystems: the arboreal, the eremial and the oreo-tundral. These movements can be
Dynamic Zoogeography
In zoogeography, as weIl as evolution, there is a continuous flow of changes,
but in the short human perspective only a small time-glimpse of the major unfolding can be witnessed. Zoogeography is in a better situation than some of the
related historico-evolutionary sciences: we are the witnesses of a major unsettling
of the animal distribution owing to the Pleistocene glaciations. In the present
period we are living through a warm interglacial with fauna gradually spreading
back over the ice- and frost-damaged areas. Lindroth (1956) has described many
cases of northward spread of animals into presently ice-free Scandinavia. According to Udvardy (1969, p.150): "Temperate and subpolar ecosystems were depleted
by the recent, drastic glaciations, and have only recently begun their renewed
evolution". This statement is true not only for the terrestrial fauna; a depletion
and destruction ofbiota also occurred in the sea.
Whereas in the open oceans the Pleistocene fluctuations caused mere advances and retreats, narrowing or widening of area, the situation was different in
the inner, mediterranean basins such as the Mediterranean and Red Seas. Here
the changes had zoogeographically defmed dimensions: whole series of species
disappeared from a given marine basin and at present are gradually returning.
Many data on this fluctuating dynamism of the Pleistocene mediterranean
biota can be found in Segerstrale (1957), Mars (1963), Peres (1967), Pusanov
(1967), and Por (1975a). These are slow decennial advances oflittoral species from
the straits connecting with the open ocean inward into the mediterranean. For
fish or plankton these are spotlike appearances of reproducing or metamorphosing swarms within sterile or larval populations that enter the sea (Fig.1).
In the mediterranean seas, depleted by Pleistocene temperature and salinity
fluctuations, the resettling process is perhaps even more marked than in the
terrestrial habitats. Repopulation proceeds only through the narrow Gibraltar or
Bosphorus Straits and the gradient of advance is very near to linear. On the other
hand, the far end of the mediterranean is a hermetically closed depauperation
area, a cul de sac comparable only to such areas as the southern tip of South
America (Darlington, 1959). In these marine cul de sacs-like the farthest Eastern
Mediterranean or the Gulf of Bothnia-the influence of the most extremely expressed environmental fluctuation is complemented by a "distance and time barrier" (Udvardy, 1969). The period of the Pleistocene fluctuation was in this case
too short for the decennially spreading species to reach the far end of the Mediterranean.
The fact that the Eastern Mediterranean and the Gulf of Suez of the Red Sea
are cul de sacs oftwo mediterranean seas had, and still has a decisive influence on
the quality and direction of the faunal interchange through the Suez Canal. This
has already been emphasized by Ben-Tuvia (1966) and Por (1971 b) and will
recurrently be discussed in the following chapters.
The above-mentioned postglacial (or interglacial) faunal adjustments are
small-step changes in which isolated species only are involved. Following Dansereau (1957) and Bänärescu and Bo~caiu (1973), the zoogeography should study the
repartition and dynamics of whole communities and ecosystems, of "syntaxons"
in their words. De Lattin (1967) also discussed Pleistocene movements in terms of
relative, often antagonistic, movements of three basic terrestrial types of ecosystems: the arboreal, the eremial and the oreo-tundral. These movements can be