Island Life; Or, The Phenomena and Causes of Insular Faunas and FlorasWallace, Alfred Russel
Science
Island Life; Or, The Phenomena and Causes of Insular Faunas and Floras
Wallace, Alfred Russel
Biogeography; Glacial epoch; Island ecology
This almost total extirpation of a luxuriant and highly peculiar vegetation
must inevitably have caused the destruction of a considerable portion of
the lower animals which once existed on the island, and it is rather
singular that so much as has actually been discovered should be left to
show us the nature of the aboriginal fauna. Many naturalists have made
small collections during short visits, but we owe our present complete
knowledge of the two most interesting groups of animals, the insects, and
the land-shells, mainly to the late Mr. T. Vernon Wollaston, who, after
having thoroughly explored Madeira and the Canaries, undertook a voyage to
St. Helena for the express purpose of studying its terrestrial fauna, and
resided for six months (1875-76) in a high central position, whence the
loftiest peaks could be explored. The results of his labours are contained
in two volumes,[69] which, like all that he wrote, are models of accuracy
and research, and it is to these volumes that we are indebted for the
interesting and suggestive facts which we here lay before our readers.
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_Insects--Coleoptera._--The total number of species of beetles hitherto
observed at St. Helena is 203, but of these no less than seventy-four are
common and wide-spread insects, which have certainly, in Mr. Wollaston's
opinion, been introduced by human agency. There remain 129 which are
believed to be truly aborigines, and of these all but one are found nowhere
else on the globe. But in addition to this large amount of specific
peculiarity (perhaps unequalled anywhere else in the world) the beetles of
this island are equally remarkable for their generic isolation, and for the
altogether exceptional proportion in which the great divisions of the order
are represented. The species belong to thirty-nine genera, of which no less
than twenty-five are peculiar to the island; and many of these are such
isolated forms that it is impossible to find their allies in any particular
country. Still more remarkable is the fact, that more than two-thirds of
the whole number of indigenous species are Rhyncophora or weevils, while
more than two-fifths (fifty-four species) belong to one family, the
Cossonidae. Now although the Rhyncophora are an immensely numerous group
and always form a large portion of the insect population, they nowhere else
approach such a proportion as this. For example, in Madeira they form
one-sixth of the whole of the indigenous Coleoptera, in the Azores less
than one-tenth, and in Britain one-seventh. Even more interesting is the
fact that the twenty genera to which these insects belong are every one of
them peculiar to the island, and in many cases have no near allies
elsewhere, so that we cannot but look on this group of beetles as forming
the most characteristic portion of the ancient insect fauna. Now, as the
great majority of these are wood borers, and all are closely attached to
vegetation and often to particular species of plants, we might, as Mr.
Public-domain text, read in full here on John Shaqi.
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