6
Dynamic Zoogeography
work by many scientists, and, not least, the war and the political situation, are
responsible for the partialloss of a great research opportunity.
Krakatau-type catastrophes and repopulations have occurred repeatedly in
geological history. Perhaps the most quoted case of a considerable geographie
dimension was the lava extrusion ofthe Deccan traps in India (de Beaufort, 1951).
Life was destroyed over a vast stretch of the Indian peninsula whieh consequently
had to be repopulated from outside.
Generally, however, such extreme annihilations are exceptions to the majority
of zoogeographie redistributions. A distributional province, as a rule, supports a
set of ecosystems and is separated by a barrier from another province occupied by
a different set of ecosystems. If the barrier is nearly hermetie the zoogeographie
pattern is stable, but as soon as the barrier breaks down, the ecosystems of the
two previously separated provinces interpenetrate. The result is a major distributional happening which changes the zoogeographieal pattern of a given part of
the globe. Barriers break down as a result of geologieal changes in the earth's
crust, or major climatie or oceanie changes which modem mankind has no
chance to witness. The artificial-or rather semi-artificial-opening of the Isthmus of Suez is the only example of a barrier breakdown whieh can be studied.
There is a gradation in the degree of tightness of the zoogeographie barriers.
According to Udvardy (1969, p.18), the topographie, physieal barriers "affeet
most animals by their ecologieal unfitness to support the dispersing pioneers".
This is the most impenetrable type ofbarrier and to this category belong the wide
stretches of sea serving as barriers for the terrestrial faunas and the continental
masses or isthmi serving as barriers for the marine faunas. In this sense, the
Isthmus of Suez was perhaps one of the most hermetie barriers of the biosphere,
despite its narrowness of only 162 km. The breakdown of a tight barrier rarely
leads to a completely unhindered intermixing of the faunas on both sides of the
old obstacle. This is especially the case when the barrier lies across a longitudinalradial pathway. The resulting "fusion faunas" are in Mayr's words (1965b) "particularly interesting as suitable material for the testing of zoogeographie methods".
When a land bridge through the emerging Central Ameriean Isthmus was
established between the two Americas, the faunal interchange was not unhindered. Using Simpson's (1965) household word, a "filtrating bridge" resulted,
whieh as a paraphrase to Udvardy (1969) is ecologieally able to support only
some of the dispersing pioneers. The Suez Canal is an aquatie replica of the
filtrating bridge: a "sieving funnel" through whieh certain taxa can pass whereas
others are retained.
The waters of the Suez Canal are not only a pathway through which dispersing pioneers are funneled, but, as convincingly shown by Steinitz (1968), they are
also a "habitat", an ecosystem in their own right. Por (1973c) has shown that the
biotie assemblage of the Bitter Lakes-the main enviro'nment of the Suez Canalhas progressed through typieal successional stages and reached a climax of its
own. This is a good example of what Udvardy (1969) calls a "living environment
barrier". In other words, the biotie associations themselves-being more or less
Dynamic Zoogeography
work by many scientists, and, not least, the war and the political situation, are
responsible for the partialloss of a great research opportunity.
Krakatau-type catastrophes and repopulations have occurred repeatedly in
geological history. Perhaps the most quoted case of a considerable geographie
dimension was the lava extrusion ofthe Deccan traps in India (de Beaufort, 1951).
Life was destroyed over a vast stretch of the Indian peninsula whieh consequently
had to be repopulated from outside.
Generally, however, such extreme annihilations are exceptions to the majority
of zoogeographie redistributions. A distributional province, as a rule, supports a
set of ecosystems and is separated by a barrier from another province occupied by
a different set of ecosystems. If the barrier is nearly hermetie the zoogeographie
pattern is stable, but as soon as the barrier breaks down, the ecosystems of the
two previously separated provinces interpenetrate. The result is a major distributional happening which changes the zoogeographieal pattern of a given part of
the globe. Barriers break down as a result of geologieal changes in the earth's
crust, or major climatie or oceanie changes which modem mankind has no
chance to witness. The artificial-or rather semi-artificial-opening of the Isthmus of Suez is the only example of a barrier breakdown whieh can be studied.
There is a gradation in the degree of tightness of the zoogeographie barriers.
According to Udvardy (1969, p.18), the topographie, physieal barriers "affeet
most animals by their ecologieal unfitness to support the dispersing pioneers".
This is the most impenetrable type ofbarrier and to this category belong the wide
stretches of sea serving as barriers for the terrestrial faunas and the continental
masses or isthmi serving as barriers for the marine faunas. In this sense, the
Isthmus of Suez was perhaps one of the most hermetie barriers of the biosphere,
despite its narrowness of only 162 km. The breakdown of a tight barrier rarely
leads to a completely unhindered intermixing of the faunas on both sides of the
old obstacle. This is especially the case when the barrier lies across a longitudinalradial pathway. The resulting "fusion faunas" are in Mayr's words (1965b) "particularly interesting as suitable material for the testing of zoogeographie methods".
When a land bridge through the emerging Central Ameriean Isthmus was
established between the two Americas, the faunal interchange was not unhindered. Using Simpson's (1965) household word, a "filtrating bridge" resulted,
whieh as a paraphrase to Udvardy (1969) is ecologieally able to support only
some of the dispersing pioneers. The Suez Canal is an aquatie replica of the
filtrating bridge: a "sieving funnel" through whieh certain taxa can pass whereas
others are retained.
The waters of the Suez Canal are not only a pathway through which dispersing pioneers are funneled, but, as convincingly shown by Steinitz (1968), they are
also a "habitat", an ecosystem in their own right. Por (1973c) has shown that the
biotie assemblage of the Bitter Lakes-the main enviro'nment of the Suez Canalhas progressed through typieal successional stages and reached a climax of its
own. This is a good example of what Udvardy (1969) calls a "living environment
barrier". In other words, the biotie associations themselves-being more or less