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AREAS OF HABITATION. 409
zoophytes, the Mediterranean has only two in common with the Red Sea,
and yet the slight sandy barrier of Suez is of relatively recent formation
in the immense series of geological ages. The slender isthmus of Central
America, which lies between the Pacific and Atlantic oceans, is an insurmountable barrier to the two faunas, and the waters separated by a distance of a few miles only are inhabited by totally different species; there
scarcely exists, Darwin tells us, a single fish, mollusk, or cetacean, which
is common to the two oceans. Even the course of the River Amazon
serves as a limit to multitudes of species; there are birds which never
venture to cross it, and whose area of habitation is strictly limited either
to the right or left bank.
In consequence of the great diversity of the present conditions of climate, soil, and food; in consequence, too, of the infinite multitude of causes
which, in the earlier ages, may have favored or hindered the development
of the species engaged in the struggle for existence, the areas occupied
by different animals are most unequal in extent. There are cetaceae, swimming birds, and echinoderms, which live in all the seas, and gnats, which
fly in clouds over the marshes of all the continents; on the other hand,
certain species are only found in a very limited region. Some reptiles
are peculiar to a single district of the Rocky Mountains or the plateau of
Utah; a certain humming-bird has been discovered in only one valley of
the Andes; every lofty volcano of Eucador, as Pichincha, Chimborazo,
and Carahuirazo, is a separate world, having its own special fauna.* In
the immense River Amazon three species of a fish called arias are found
only to the west of the Island Marajo, in a space of scarcely two leagues,
at the place where the mingling of the mud raised by the conflict of the
sea and river takes place.f
Besides, the different areas of habitation change incessantly during the
course of ages, according to the modifications of soil and climate. Man,
too, who is also a geological agent, and one of the most active, has taken
an enormous part, either directly or indirectly, in the distribution of animals ;l but apart from this decided influence due to human intervention,
it is certain that all the variations of the surrounding circumstances produce corresponding variations in the distribution of species. If cold or
heat increase in a country, the winds become stronger or weaker, the rains
increase or diminish; or if the soil be renewed by alluvium, or saturated
with salt by an irruption of the sea, or if a marsh be formed or dried up,
a number of species of animals will advance or retreat to find conditions
of existence which are more favorable to them, and also to seek food which
suits them. Thus various birds of the Upper Engadine have established
themselves in the lower valleys, and the magpie has even entirely quitted
the district.§ This is a phenomenon which all naturalists have observed:
they have even ascertained many apparently inexplicable examples of
migrations, so imperceptible to man have been the modifications of cir-
* Moritz Wagner. + Da Silva Continho.
t See below, the section entitled The Work of Man. § Michelet, la Montagne.
| Title | The ocean, atmosphere, and life |
| Creator | Reclus, Elisée |
| Publisher | Harper |
| Place of Publication | New York |
| Date | 1873 |
| Language | eng |
| Type | Books/Pamphlets |
| Title | 00000452 |
| Type | Books/Pamphlets |
| Transcript | AREAS OF HABITATION. 409 zoophytes, the Mediterranean has only two in common with the Red Sea, and yet the slight sandy barrier of Suez is of relatively recent formation in the immense series of geological ages. The slender isthmus of Central America, which lies between the Pacific and Atlantic oceans, is an insurmountable barrier to the two faunas, and the waters separated by a distance of a few miles only are inhabited by totally different species; there scarcely exists, Darwin tells us, a single fish, mollusk, or cetacean, which is common to the two oceans. Even the course of the River Amazon serves as a limit to multitudes of species; there are birds which never venture to cross it, and whose area of habitation is strictly limited either to the right or left bank. In consequence of the great diversity of the present conditions of climate, soil, and food; in consequence, too, of the infinite multitude of causes which, in the earlier ages, may have favored or hindered the development of the species engaged in the struggle for existence, the areas occupied by different animals are most unequal in extent. There are cetaceae, swimming birds, and echinoderms, which live in all the seas, and gnats, which fly in clouds over the marshes of all the continents; on the other hand, certain species are only found in a very limited region. Some reptiles are peculiar to a single district of the Rocky Mountains or the plateau of Utah; a certain humming-bird has been discovered in only one valley of the Andes; every lofty volcano of Eucador, as Pichincha, Chimborazo, and Carahuirazo, is a separate world, having its own special fauna.* In the immense River Amazon three species of a fish called arias are found only to the west of the Island Marajo, in a space of scarcely two leagues, at the place where the mingling of the mud raised by the conflict of the sea and river takes place.f Besides, the different areas of habitation change incessantly during the course of ages, according to the modifications of soil and climate. Man, too, who is also a geological agent, and one of the most active, has taken an enormous part, either directly or indirectly, in the distribution of animals ;l but apart from this decided influence due to human intervention, it is certain that all the variations of the surrounding circumstances produce corresponding variations in the distribution of species. If cold or heat increase in a country, the winds become stronger or weaker, the rains increase or diminish; or if the soil be renewed by alluvium, or saturated with salt by an irruption of the sea, or if a marsh be formed or dried up, a number of species of animals will advance or retreat to find conditions of existence which are more favorable to them, and also to seek food which suits them. Thus various birds of the Upper Engadine have established themselves in the lower valleys, and the magpie has even entirely quitted the district.§ This is a phenomenon which all naturalists have observed: they have even ascertained many apparently inexplicable examples of migrations, so imperceptible to man have been the modifications of cir- * Moritz Wagner. + Da Silva Continho. t See below, the section entitled The Work of Man. § Michelet, la Montagne. |
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