Dynamic Zoogeography
Zoogeography, like paleontology and evolution research is a historical-descriptive discipline. The conclusions are circumstantial and largely derived from
comparative reasoning. In very few cases, and only at a microlevel, can the real
dynamism be observed and hints be obtained of the deterministic network of the
major, historical macrophenomena. In the modern man-molded ecosystems some
evolutionary processes became accelerated and thus observable. However, without being entirely artificial epiphenomena, the human-influenced happenings are
to a large extent new events in an evolving biosphere. Animals are selected naturally as well as artificially to coincide with the presence and needs of the human
species. Animals preadapted or adapted to adventive spread as "camp followers",
"hitch-hikers", etc., are the only ones which take advantage of human mobility.
Lindroth (1956) draws a convincing picture ofthe set of adaptations which enable
insects to cross the Atlantic from Europe to America as adventives on ships. A
similar picture could probably also be drawn for the ecological valence which
enables a marine organism to become an adventive diaspore on a ship's hull. To
my knowledge, no listing of these qualities has ever been made. A fouling-cosmo~
polite is an animal with a sessile life, a nonspecific filter feeder, very adaptative
in its reproduction requirements, euryhaline, resistant to current, and resistant to
pollutants.
All these characteristics ipso facto also guarantee the spread of the shipcarried pioneers in their new environment, and ensure their competitive success
against the local fauna.
As with other shipping lanes, the Suez Canal also served to spread the adventive marine fauna. There is no doubt that some of the well-known cosmopolitan
fouling organisms of eastern origin such as M ercierella enigmatica (Polychaeta) 1
and Elminius modestus (Cirripedia) took advantage of the short sailing time
through the Suez Canal and thus succeeded in their advance. It has however, by
no means been proved that the Suez Canal was the only or necessary way to
spread them into the Western hemisphere.
In the following treatment of Lessepsian migration I shall not consider the
cosmopolitan fouling organisms. Their spread has nothing to do with the specific
problem of Lessepsian migration. The emphasis williie on the natural dynamism
of the spreading phenomena, someof which include, however, some passive
dispersal.
1 Zibrowius (1973) recently questioned the alleged worldwide distribution of this species.
Zoogeography, like paleontology and evolution research is a historical-descriptive discipline. The conclusions are circumstantial and largely derived from
comparative reasoning. In very few cases, and only at a microlevel, can the real
dynamism be observed and hints be obtained of the deterministic network of the
major, historical macrophenomena. In the modern man-molded ecosystems some
evolutionary processes became accelerated and thus observable. However, without being entirely artificial epiphenomena, the human-influenced happenings are
to a large extent new events in an evolving biosphere. Animals are selected naturally as well as artificially to coincide with the presence and needs of the human
species. Animals preadapted or adapted to adventive spread as "camp followers",
"hitch-hikers", etc., are the only ones which take advantage of human mobility.
Lindroth (1956) draws a convincing picture ofthe set of adaptations which enable
insects to cross the Atlantic from Europe to America as adventives on ships. A
similar picture could probably also be drawn for the ecological valence which
enables a marine organism to become an adventive diaspore on a ship's hull. To
my knowledge, no listing of these qualities has ever been made. A fouling-cosmo~
polite is an animal with a sessile life, a nonspecific filter feeder, very adaptative
in its reproduction requirements, euryhaline, resistant to current, and resistant to
pollutants.
All these characteristics ipso facto also guarantee the spread of the shipcarried pioneers in their new environment, and ensure their competitive success
against the local fauna.
As with other shipping lanes, the Suez Canal also served to spread the adventive marine fauna. There is no doubt that some of the well-known cosmopolitan
fouling organisms of eastern origin such as M ercierella enigmatica (Polychaeta) 1
and Elminius modestus (Cirripedia) took advantage of the short sailing time
through the Suez Canal and thus succeeded in their advance. It has however, by
no means been proved that the Suez Canal was the only or necessary way to
spread them into the Western hemisphere.
In the following treatment of Lessepsian migration I shall not consider the
cosmopolitan fouling organisms. Their spread has nothing to do with the specific
problem of Lessepsian migration. The emphasis williie on the natural dynamism
of the spreading phenomena, someof which include, however, some passive
dispersal.
1 Zibrowius (1973) recently questioned the alleged worldwide distribution of this species.