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_THE CONTEMPORARY SCIENCE SERIES._
Edited by HAVELOCK ELLIS.
THE HISTORY OF THE EUROPEAN FAUNA
THE HISTORY OF THE
EUROPEAN FAUNA
R. F. SCHARFF, B.Sc., Ph.D., F.Z.S.
_Keeper of the Natural History Collections, Science and Art Museum,
Dublin; Member of the Royal Irish Academy; Corresponding
Member of the Senckenbergische Naturforschende Gesellschaft._
WITH ILLUSTRATIONS.
LONDON
WALTER SCOTT, LIMITED
PATERNOSTER SQUARE
1899
CONTENTS.
PAGE
CHAPTER I.
INTRODUCTION 1-36
CHAPTER II.
PRELIMINARY CONSIDERATIONS 37-88
CHAPTER III.
THE FAUNA OF BRITAIN 89-131
CHAPTER IV.
THE ARCTIC FAUNA 132-188
CHAPTER V.
THE SIBERIAN MIGRATION 189-244
CHAPTER VI.
THE ORIENTAL MIGRATION 245-286
CHAPTER VII.
THE LUSITANIAN FAUNA 287-308
CHAPTER VIII.
THE ALPINE FAUNA 309-350
BIBLIOGRAPHY 351-354
INDEX 355-364
PREFACE.
Our knowledge of the present and past fauna of Europe is as yet
insufficient to indicate with precision the original homes of its
component elements, but I hope that the lines of research laid down
here, and the method of treatment adopted, will aid zoologists and
geologists in collecting materials for a more comprehensive study of the
history of our animals. I trust also that a fresh impulse will be given
by the publication of this book to the study of the Geographical
Distribution of Species. Collectors of Beetles, Butterflies, Shells, and
Fossils may derive some useful hints by its perusal and thus direct
their studies, so as to add, by accuracy in observation, to our
knowledge of the former geographical revolutions which have moulded our
islands and continents. To geographers, a survey of some of the more
important changes in the distribution of land and water in past
times--based upon the composition of our fauna--will be interesting. The
subject, however, is a complex one. I have ventured to indicate a
suitable method of treatment, and as such this attempt to elucidate the
history of the European fauna should be received.
This work was written as the outcome of a paper published in the
_Proceedings of the Royal Irish Academy_ (3rd series, vol. iv., 1897),
"On the Origin of the European Fauna." A summary of that paper appeared
in _Nature_ (vol. lvi., 1897), and fuller extracts of more important
parts, with some criticisms, in the _Geological Magazine_ (N.S., sec.
iv., vol. iv., 1897). I freely acknowledge the value of these
criticisms, which have largely assisted me to amplify and to improve
upon the ideas laid down in the paper.
I have found that it greatly facilitates comprehension of the arguments
used, to give a few maps indicating in a general way the extent of
former seas and continents. I may in this way, as Mr. Kendall has
pointed out, have submerged many square miles of land which had never
been covered by the sea,--at least not within recent geological
times,--but the maps were intended as illustrations of my views in a
broad spirit only.
Some zoologists may be surprised that, in some cases, I have not
followed the latest views in revised nomenclature. I felt that in a work
of this kind it was of supreme importance to employ names still current
in our leading text-books, such as _Lepus variabilis_ for the Mountain
Hare, instead of _Lepus timidus_. After each chapter I have endeavoured
to give a short summary of contents, while a bibliography of the
principal works and papers consulted will be found at the end. I should
also acknowledge the aid which I have received from such excellent
works of reference as the British Museum Catalogues of Birds, by Dr.
Bowdler Sharpe, and those of Reptiles, Amphibia, and Fishes, by Dr.
Guenther and Dr. Boulenger. The valuable works on Mammalia by Sir W.
Flower, Mr. Lydekker, Mr. Greve, and Dr. Trouessart, were indispensable
to me.
To Sir William Flower, Mr. Lydekker, Professor Sars, and Professor
Smitt, I am especially indebted for allowing me to reproduce drawings
from their works, and to my friend Mr. Welch for some beautiful
photographs. The Council of the Royal Irish Academy also kindly gave me
permission to reprint the maps used in illustration of my paper.
Professor Haddon first suggested my writing this book, and gave me many
useful hints; and great assistance was rendered me by my colleague, Mr.
G. H. Carpenter, in revising the proofs. To both of these kind friends I
desire to acknowledge my deep sense of gratitude.
R. F. SCHARFF.
THE HISTORY OF THE EUROPEAN FAUNA.
CHAPTER I.
INTRODUCTION.
Every student of natural history, whether he be interested in birds,
butterflies, or shells, contributes his share of facts which help to
show how the fauna of his country has originated. The capture of a
Swallow-tail or of a Marbled White Butterfly in England at once
furnishes material for reflection as to the reason of its absence from
Scotland and Ireland. Why should the Nightingale allow its beautiful
song to be heard in England, and never stray across the Channel to the
sister isle or cross the borders of North Britain? Lovers of bird-life
and sportsmen, who have observed the habits of the Ptarmigan in the wild
mountain recesses of Scotland, are aware that nowhere else in the
British Islands do we meet with this interesting member of the grouse
family, and many no doubt have allowed their minds to dwell upon the
causes of its singularly local distribution.
All these animals have a wide range in other parts of the world. In
past times, before man began to make observations on the geographical
distribution of birds and butterflies, or even before the appearance of
man in Northern Europe, they may have lived all over the British
Islands. For some reason or other they are perhaps dying out or
withdrawing towards their original home, which may either be northward,
or to the east or south. If we had some clue as to their former history
from fossil evidence--or, in other words, if their remains had been
preserved to us in geological deposits,--we should have less difficulty
in deciding this problem. But butterflies are scarcely ever preserved in
a fossil state, and birds very rarely. We know little or nothing,
therefore, of their past history from direct evidence, and are obliged
to trust to indirect methods of research which will be indicated later
on.
Mammals and Snails tell us their story more plainly. The bones of the
former and the shells of snails are easily preserved, and thus furnish
us with the necessary data as to their past history, for we find them
abundantly in most of the recent geological deposits. Among the mammals
of the British Islands there are some instances of distribution which
much resemble those I have quoted. Thus the Arctic Hare (_Lepus
variabilis_) is in the British Islands confined to Ireland and to the
mountains of Scotland; and if it were not for the fact that its bones
have been discovered in a cave in the south-west of England, we should
perhaps never have known that, formerly, it must have inhabited that
country as well. Of other mammals we possess fossil and also historical
evidence of their having once lived in these islands. Such are the Wolf
and the Wild Boar, both of which were abundant in Great Britain and
Ireland. The latter is a distinctly southern species. We assume this,
because its remains have never been found in high northern latitudes;
nor does it now occur in Northern Europe or Northern Asia, whilst all
its nearest relatives live in sub-tropical or tropical climates. The
Arctic Hare, on the contrary, has probably come to us from the north.
Its remains are unknown even in Southern Europe, and the more we
approach the Arctic Regions, the more abundant it becomes. Thus we have
here two instances of British mammals, one of which, the Wild Boar, has
died out--as it were in a southerly direction; whilst the other, the
Arctic Hare, is apparently retreating towards the north.
There are also some British mammals of which we have no fossil history,
at least of which no remains have as yet been found in these islands.
Such a one is the Harvest Mouse (_Mus minutus_). It has a somewhat
restricted range in England, and only just crosses the Scottish border
in the east. From the rest of Scotland and from the whole of Ireland it
is absent. To judge from this distribution, in connection with the fact
of its being unknown as a British fossil species, it is probably a late
immigrant to England, and has not had time to spread, throughout
Scotland at any rate. But it is also absent from Scandinavia, from the
Spanish peninsula, from almost the whole of Italy and the Alps, as also
from the Mediterranean Islands, whilst the little mouse occurs
abundantly right across Siberia. We shall learn more about centres of
dispersion later on; meanwhile I should mention that such a distribution
indicates that the Harvest Mouse has most likely originated in the east,
and has spread from there westward in recent geological times.
Conchologists have long ago been acquainted with the fact that many
molluscs, for example the so-called "Stone-cutter" Snail (_Helix
lapicida_) and the "Cheese Snail" (_Helix obvoluta_), have a very
restricted range in the British Islands. Both are entirely absent from
Scotland and Ireland, the Cheese Snail being confined to South-eastern
England. The Stone-cutter has rather a wider range, is even known from a
Welsh locality, and is met with as far north as Yorkshire. Their
distribution would indicate, therefore, that while both are recent
immigrants, the Cheese Snail is probably the last comer. This
supposition is in so far supported by fossil evidence, as the latter is
unknown in the fossil state, whilst the Stone-cutter has been described
by Messrs. Kennard and Woodward (p. 243)[1] as occurring in the cave
deposit known as the Ichtham fissure, and also from several English
pleistocene and holocene deposits. The Stone-cutter can scarcely be
looked upon as a very recent immigrant in the light of this evidence,
though we have no proof of its having ever had a much wider range in the
British Islands than it has to-day.
Among the lichens, which so abundantly cover the rocks and trees in
South-western Ireland, and which impart such a characteristic feature to
the scenery, we find a beautifully spotted slug (_Geomalacus
maculosus_).[2] It is a stranger to the rest of the British Islands, and
indeed occurs nowhere else in Northern Europe. We have to travel as far
as Northern Portugal before we again meet with it, and it is there also
that its nearest relations live.
Many more similar examples might be quoted, but enough, I think, has
been said to show that the British fauna is made up of several elements
whose original homes may lie widely apart and in different directions.
We have fossil evidence that some of the northern species, and also a
few of the southern ones, have become extinct within comparatively
recent times; others are apparently on the verge of extinction, whilst
many not only maintain their position in the constant struggle for
existence, but are even extending their range.
The problem of tracing the origin of the British fauna, or at least that
of some of the more characteristic members of every section or element,
appears at first a somewhat difficult task. Indeed, the means of
dispersal of the various groups of animals are so different that it
occurred to me it might be better to deal with the mammals, the birds,
the reptiles, and so forth, all separately. This idea I have attempted
to follow to some extent, with most satisfactory results. The British
fauna of the present day is no doubt complex, but no more so than the
fauna of the most recent of our geological deposits--the Pleistocene.
However, when we go back still further and look at the earlier Tertiary
remains, we find the fauna becoming less complex. Northern species
disappear, and the strata are entirely filled with the remains of
southern animals and plants. Geologists indeed are quite unanimous in
their belief, that the fauna of the British Islands during the earlier
epochs of the Tertiary Era was a southern one; that it then gradually
became more temperate, until at last, in more recent times, decidedly
northern forms invaded the country. These seem to have driven out--to
some extent at least--the southern species; but more recently again, the
southerners, reinforced by an eastern contingent, appear to have gained
territory and are advancing into the area held by the northerners. The
eastern invasion does not seem to have affected Ireland at all, and we
find the country there divided between the southern and northern
animals. We can thus roughly construct a map as I have done here,
showing, by means of horizontal and sloping lines, the principal areas
inhabited at the present time by the species of northern, southern, and
eastern origin (Fig. 1).
[Illustration: Fig. 1.--Map of the British Islands, indicating
approximately the areas inhabited by the northern, southern, and eastern
animals. The horizontal lines represent the areas of northern species,
the sloping lines those of southern and eastern ones.]
In the problems which are being discussed in this work I have often
found it of advantage, in order to facilitate the comprehension of the
arguments used, to give maps. Some of these represent the geographical
conditions at the particular epoch referred to in the text, but they
merely claim to give a general idea. There was never any intention to
make them correspond with all the data of which we have geological
evidence. They are what I might call "diagrammatic." In comparing them
with reconstructions of former physical geography such as have been
attempted from time to time, I hope geologists will therefore deal
leniently with the faults I may have committed, and remember that the
maps are "impressions," or "diagrams," and not faithful representations
of all the geographical revolutions witnessed by some of our remote
forefathers at any particular period.
The knowledge we gain from a study of the British Tertiary deposits
enables us to affirm positively that both the eastern and the northern
species arrived in these islands comparatively recently, but that the
southern forms must have migrated northward from the Continent long ages
ago. Since the northern and the eastern migrations--that is to say,
those coming from the north and east--were the last to arrive in
Northern Europe, the remains of the animals contained in the most recent
deposits of that portion of our continent will furnish us with a clue as
to the extent of the area inhabited by them. This is not all, however.
It is also possible to discover from these remains the direction which
the animals that they belonged to came from. As we shall learn later
on, a migration on a vast scale entered Europe during the Pleistocene
epoch--the most recent of the geological epochs, during which great
extensions of glaciers occurred in the mountainous regions of Europe.
The latter period is known to us as the Ice Age or Glacial period. This
will be described more fully in Chapter II., meanwhile I may mention
that we presume that this migration came from the east, because no
remains of the members of that particular fauna are known from Spain,
Southern Italy, Scandinavia, Ireland, or from the Balkan peninsula. The
number of species evidently belonging to this same migration, moreover,
become fewer as we proceed westward, and a large proportion of them
still inhabit Northern Asia, though most of them are now extinct in
Europe. After having thoroughly studied such a recent geological
migration, we learn to understand others better, though the more ancient
they are, the fewer are the traces and the more difficult are they to
follow.
Then again we have to take into consideration the fact, that whilst
mammals, particularly the larger herbivores, are forced to migrate
frequently owing to scarcity of food or temporary changes of climate,
many of the invertebrates remain practically unaffected by either. Most
of our land mollusca, for instance, are satisfied with meagre provender,
and stand extremes of climate well, as long as there is sufficient
moisture. As a result of their peculiar disposition, many of them, no
doubt, have survived through several geological epochs, and have
witnessed vast geographical revolutions in their immediate surroundings,
whilst mammals are comparatively short-lived. Being driven from one
country to another, and exposed to innumerable enemies, new types appear
and old ones rapidly vanish; in fact, there are almost constant changes
in the mammalian fauna as we pass from one epoch to another.
I have until now referred more particularly to the British fauna and the
North European in general, because the history of our own animals
interests us all more than those of any other European area. It is,
moreover, preferable to commence our investigations into the origin of
the European fauna by the study of a small district. This should, if
possible, be an island. If we took a slice of the continent like France
or Germany, we should find the problem more complex. Instead of choosing
the British Islands, we might, however, take an island like Corsica or
Sardinia. In either of these we should discover peculiarities in the
composition of their fauna precisely similar to those which I have
indicated to be present in the British fauna. We should find probably a
more striking endemic[3] element, which with us is so meagre that it
can almost be left unnoticed; the main features, however, remain nearly
the same. The fauna of both of these islands is composed of a strong
southern element, of an eastern and a northern one, and in addition we
have here species whose ancestors lived in Western Europe.
Before investigating more minutely the problems suggested by the
composition of the faunas of these insular and also of some continental
areas, it is necessary that we should thoroughly understand all about
the migrations of animals. One of the principal objects of this work is
to show how the autochthonous animals of Europe, _i.e._, those which
have originated there, may be distinguished from the immigrants, and to
trace the latter to the home of their ancestors. But in doing so, it is
necessary to refer to the many important geographical changes which have
occurred in Europe during the latest geological epochs. The study of the
geographical distribution of the European fauna, as expounded in this
work, will in many instances confirm the theories as to geographical
changes based upon geological foundations. But in every case the views
herein advocated are founded upon the geographical distribution of
living and extinct organisms alone.
A terrestrial mammal like the deer can, under ordinary circumstances,
only reach one part of a country from another by walking or running to
it; but a beetle, such as the cockchafer, has two different modes of
progression. It may walk or fly. In both, however, there is a third mode
of transport--an involuntary one. The deer may be suddenly seized by a
flood whilst crossing a river, and carried far away without necessarily
coming to grief. The beetle in a similar manner could be transported to
a distant country, or it might be caught in a whirlwind and blown
hundreds of miles off.
We may thus distinguish between the natural or active and the accidental
or passive means of distribution of animals. The active mode of
dispersal again may be only migratory, as in most animals, or periodic
and migratory, as in some birds and fishes. It is of course the tendency
of every species to spread in all directions from its original home,
provided it does not encounter obstacles, such as want of food,
unsuitability of climate or soil, or barriers such as mountains, rivers,
or the sea. Birds might be thought to be little interfered with by any
of these barriers, but, as Dr. Wallace has shown, they are almost as
much affected by them in their distribution as mammals are.
This then is the ordinary migratory distribution. Periodic distribution
obtains with migratory birds and fishes. The annual flight of swallows
to their northern summer residence comes under the heading of periodic
migration or distribution, but apart from this, the swallow must seek to
extend its range by the ordinary method, like every other animal.
Similarly, the herring migrates periodically into shallow water to
spawn, only to return again to its deeper home, where, as its numbers
increase, there must be a tendency to spread. We have in these cases,
therefore, both a periodic and an ordinary movement of migration.
Now, in studying the composition of a fauna, and especially its origin,
it is of the utmost importance to be able to determine approximately the
percentage of accidental arrivals and of the ordinary migrants--that is
to say, of those which have reached the country owing to accidental
distribution, and of animals which have adopted the usual course of
migration. It is of all the more import to review this subject of
accidental, or, as Darwin called it, "the occasional means" of
distribution, as both he and Dr. Wallace have, I venture to think,
somewhat over-estimated its significance. No one doubts that accidental
transportal takes place, but the question is whether the accidentally
transported animals arrive living and reach a spot where suitable food
is procurable, and whether they are able to propagate their own species
in the new locality. For it must be clear to anybody that the accidental
transportal of a beetle or of a snail to a new country cannot affect its
fauna or add one permanent member to it unless all these conditions are
fulfilled. As a matter of fact, only exceedingly few instances are on
record of man having witnessed, for example, the accidental transportal
across the sea to an island of a live animal.
To mention an example, Colonel Feilden informs us (_Zoologist_, 1888)
that, when living on the island of Barbadoes, an alligator arrived one
day on the shore, and at the same time a tree measuring 40 feet in
length, which was recognised as a Demerara species, was likewise
stranded. He thinks that there can be no doubt that the alligator, which
was alive when it reached Barbadoes, was transported by the tree, thus
covering a distance of 250 miles from the nearest land. Numerous
observations on the accidental transportal of seeds and tree-trunks from
one island to another, and from a continent to an island, have been
recorded, and even on our own shores we may witness the occasional
arrival of such vegetable products from a far distant land. On the west
coast of Ireland it not unfrequently happens that large West Indian
beans are stranded, and in this as well as in many other similar cases
the seeds have often proved none the worse for their prolonged immersion
in sea-water. That locusts are sometimes blown to great distances from
the land is not so surprising, since their power of steering through the
air is very limited. Darwin mentions (p. 327) having caught one 370
miles from the coast of Africa, and that swarms of them sometimes
visited Madeira. Sir Charles Lyell relates that green rafts composed of
canes and brush-wood are occasionally carried down the Parana River in
South America by inundations, bearing on them the tiger, cayman,
squirrels, and other quadrupeds.
But though actual observations of such abnormal instances of the
dispersal of animals are few, many experiments have been made to
demonstrate the possibility of a passive transportal of species over
wide distances. It was especially Darwin who gave a great stimulus by
setting the example to those interested in natural history in the
conduct of such researches. He was struck by the fact that, though
land-shells and their eggs are easily killed by sea-water, almost all
oceanic islands, even the smallest and most isolated, are inhabited by
them, and felt that there must be some unknown but occasionally
efficient means for their transportal (p. 353). To quote his words: "It
occurred to me that land-shells, when hibernating and having a
membranous diaphragm over the mouth of the shell, might be floated in
chinks of drifted timber across moderately wide arms of the sea. And I
find that several species in this state withstand uninjured an immersion
in sea-water during seven days: one shell, the _Helix pomatia_, after
having been thus treated and again hibernating, was put into sea-water
for twenty days, and perfectly recovered. During this length of time the
shell might have been carried by a marine current of average swiftness
to a distance of 660 geographical miles. As this _Helix_ has a thick
calcareous operculum, I removed it, and when it had formed a new
membranous one, I again immersed it for fourteen days in sea-water, and
again it recovered and crawled away. Baron Aucapitaine has since tried
similar experiments: he placed one hundred land-shells, belonging to ten
species, in a box pierced with holes, and immersed it for a fortnight
in the sea. Out of the hundred shells, twenty-seven recovered. The
presence of an operculum seems to have been of importance, as out of
twelve specimens of _Cyclostoma elegans_ which it thus furnished, eleven
revived. It is remarkable, seeing how well the _Helix pomatia_ resisted
with me the salt-water, that not one of fifty-four specimens belonging
to four other species of _Helix_ tried by Aucapitaine, recovered. It is,
however, not at all probable that land-shells have often been thus
transported; the feet of birds offer a more probable method."
We have here positive evidence that such shells as _Helix pomatia_ and
_Cyclostoma elegans_ might easily be transported to an island from the
mainland. The former occurs in France, Holland, and England, and the
latter all along western continental Europe and England. And yet neither
of these species inhabits the Canary Islands, Madeira, or Ireland, none
of which are at too great a distance from Europe to be within easy reach
for a floating object. The fact that _Cyclostoma elegans_ does not live
in Ireland is of particular interest in connection with the
floating-theory just quoted, as on all sides of Ireland dead specimens
have been picked up on the shore, showing that marine currents carry
specimens and have thus transported them for countless centuries.
Nevertheless the species has not established itself in Ireland. If such
a fate meets a land-shell of the type of _Cyclostoma elegans_, it may be
asked, with some justification, what chance slugs or the smaller
non-operculated species would have to reach an island like Ireland
alive from the mainland, and to colonise it successfully.
Both slugs and their eggs are killed by a short immersion in sea-water,
as I have proved experimentally. I have also subjected slugs, in the act
of crawling on twigs, to an artificial spray of sea-water. This seemed
to irritate their tender skins to such an extent that they curled
themselves up, released their hold on the twig and let themselves drop
to the ground. If we supposed, therefore, that a slug had successfully
reached the sea, transported on a tree-trunk, the moisture would tend to
lure it forth from its hiding-place under the bark, whilst the mere
spray would prove fatal to its existence. Those species of snails and
slugs which lead an underground existence, rarely venturing above
ground, such as _Testacella_ and _Coecilianella_, would have even less
chance of being accidentally carried to some distant island.
The suggestion advanced by Darwin (p. 353), that young snails just
hatched might sometimes adhere to the feet of birds roosting on the
ground and thus be transported, appears to me so extremely improbable as
to be scarcely worth serious consideration. Indeed, as Darwin himself
acknowledged later on, it does not help us very much to suggest possible
modes of transport. What we require is direct evidence. How far we are,
however, from obtaining it, may be inferred from Mr. Kew's remark (p.
119), that "we have little or no actual evidence of precise modes of
dispersal even for short distances on land."
A very curious statement was made by a well-known French conchologist,
the late M. Bourguignat, with regard to introductions of mollusca.
Whether he had any actual facts collected in support of it, I cannot
say, but he maintained that species accidentally transported, with the
exception of those under maritime influence, can only be acclimatised
from north to south, and not from south to north--from east to west, but
not from west to east (p. 353).
The whole theory of the accidental or abnormal dispersal of mollusca
appears to have been originated by Darwin, in order to account for their
presence on so-called _Oceanic islands_. His views were strongly
supported by Wallace, who defines these islands (p. 243) as those which
are of volcanic or coralline formation usually far from continents,
entirely without indigenous land mammals or amphibians, but with a fair
number of birds and insects, and usually with some reptiles.
I do not wish it to be understood that I am in any way undervaluing the
great works of these distinguished naturalists. Darwin's views have had
more influence in advancing Zoology than those of any man, and his fame
is unassailable. Nevertheless, I feel that his theories regarding the
origin of the faunas of oceanic islands require revision.
The formerly prevalent belief of the permanence of ocean basins has been
shaken by the utterances of some of the greatest geologists of our day,
whilst many positively assert that what is now deep sea of more than
1000 fathoms was dry land within comparatively recent geological epochs.
Thus the Azores are classed by Darwin and Wallace among the oceanic
islands--that is to say, among such as have received their fauna and
flora by flotsam and jetsam. But Professor Neumayr believes, on
geological grounds, that the Old and New Worlds were connected by a
land-bridge during Tertiary times right across the Atlantic, and that
the Canary Islands, Madeira, and Azores (p. 547) are the last remnants
of this continent. This meets with the entire approbation of Dr. von
Ihering, who has recently re-investigated the subject from a faunistic
point of view (p. 135). Take another instance of one of Wallace's most
typical oceanic islands, the Galapagos Group. Their fauna and flora have
recently been most thoroughly re-explored by an American expedition, the
result of which, according to Dr. Baur, goes to show that these islands
must have formed part of the mainland of South America at no distant
date. The fauna and flora are therefore to be regarded as having reached
them in the normal mode, viz., by migration on land. According to Mr.
Beddard (p. 138), it is difficult to see how earthworms could be
transported across the sea. Floating tree-trunks have been observed far
out at sea, but unless the water remained absolutely calm during the
long period necessary for the drifting by currents so that no splashing
occurred, the worms would probably be killed. Yet earthworms do occur
on oceanic islands. It is indeed quite possible that our views with
regard to the origin of the remainder of the Pacific Islands may change
very materially, and once more revert to what Dr. Gould expressed nearly
fifty years ago in the following words: "From a consideration of the
land-shells on the Pacific Islands, it seems possible to draw some fair
inferences as to the relations of the lands which once occupied the area
of the Pacific Ocean, and whose mountain peaks evidently now indicate or
constitute the islands with which it is now studded." Indeed Dr. von
Ihering goes so far as to positively state that in his opinion the
Polynesian Islands are not volcanic eruptions of the sea floor, which
being without life were successively peopled from Australia and the
neighbouring islands, but the remains of a great Pacific continent,
which was in early mesozoic times connected with other continental land
masses (_a_, p. 425).
Before coming to a decision on the part played by flotsam and jetsam in
the constitution of an island fauna, those who have studied the problem
on the spot should, however, have a voice in the matter. And though,
from my experience in northern latitudes, I feel sure that island faunas
there are but slightly affected by occasional dispersal of species, Mr.
Hedley, who has made the fauna of the Pacific Islands his special study,
assures me that drift migration plays an important _role_ in that
region. I hope we may soon have a more detailed account of his
particular observation bearing on this interesting subject.
On the other hand, Mr. Simpson, who has gained considerable experience
of oceanic dispersal in the West Indian region, though he acknowledges
having often noticed bamboo rafts, which would be suitable in the
transportal of invertebrates, nevertheless does not attach much
importance to this means of distribution. "The fact," he remarks, "that
the operculates (operculate land-shells) form so large a proportion of
the Antillean land-snail fauna, that a majority of the genera are found
on two or more of the islands and the mainland, while nearly every
species is absolutely restricted to a single island, appears to me to be
very strong testimony in favour of a former general land connection" (p.
428).
Amphibians are affected in the same manner by sea-water as slugs are.
The accidental transportal of an amphibian from the mainland to an
island is therefore almost inconceivable. And the presence of frogs,
toads, and newts in the British Islands, in Corsica and Sardinia,
indicates, if nothing else did, that all these islands were at no
distant date united with the continent of Europe.
As regards the terrestrial reptiles, the case is somewhat different.
Many of them readily take to the sea, and, as probably all snakes and
some lizards are able to swim, it is possible that sometimes, though
very rarely, they might reach islands if not too far from a continent.
Instances of accidental transportal of land-reptiles to islands have
actually been observed. But the fact of the occurrence of such instances
by no means proves that reptiles thus conveyed are able to establish
themselves permanently in their new home. Sir Charles Lyell records in
his _Principles of Geology_ that a large boa-constrictor was once seen
floating to the island of St. Vincent, twisted round the trunk of a
tree. It appeared so little injured by its long voyage from South
America, that it captured some sheep before it was killed.
Mammals might be accidentally conveyed to islands on such rafts as have
been described by Sir Charles Lyell, and there are instances on record
of their having crossed short distances of sea by swimming. Elephants
and also deer and pigs are good swimmers, the former having been known
to swim for six hours at a stretch. "But," remarks Mr. Lydekker (p. 13),
"it may be assumed that about twenty miles is the utmost limit which
mammals are likely to cross by swimming, even when favoured by currents.
Such passages as these must, however, be of very rare occurrence, for a
terrestrial mammal is not likely to take it into its head to swim
straight out to sea in an unknown direction. Moreover, supposing a
mammal, near to a particular island, to have arrived there by swimming,
unless it happen to be a pregnant female, or unless another individual
of the same species but of the opposite sex should arrive soon after (a
most unlikely event), it would in due course die without being able to
propagate its kind."
All zoologists, indeed, are quite in accord with Dr. Wallace's view as
expressed in _Island Life_ (p. 74). "Whenever we find that a
considerable number of the mammals of two countries exhibit distinct
marks of relationship, we may be sure that an actual land-connection, or
at all events an approach to within a very few miles of each other, has
at one time existed." As all the European islands come under this
category, their mammals exhibiting distinct relationship with those on
the European continent, they all have been connected with it formerly.
Perhaps the most powerful of all agents in the transportal of species by
accidental means is man. But his actions may be accidental as well as
intentional. We have therefore to distinguish between the animals
disseminated all over the world by pure chance, and those which have
been introduced into new countries purposely. Invertebrates, such as
snails, centipedes, woodlice, beetles, and cockroaches, are constantly
being unintentionally carried with vegetables, fruit, trees, and with
timber from one country to another. Earthworms are sometimes transported
in the balls of earth in which the roots of trees are enveloped. As
regards molluscs, Mr. Kew believes (p. 178) that during the last three
centuries at least, human agency has influenced their disposal more than
all other causes taken together. A large number of species of
invertebrates in America are said to owe their existence in that country
to accidental introduction by man. In most cases, however, no
particular reason can be assigned why they should have been thus
introduced, and as a matter of fact there are always individual
differences of opinion as to the precise number of such. Certain it is,
that though the number of supposed introductions from Europe to America
is very large, those which have been carried from America to Europe is
exceedingly small. In fact, I remember only two instances of accidental
animal importations from America which have firmly established
themselves in Europe, viz., a small fresh-water mollusc, _Planorbis
dilatatus_, and the much-dreaded vine-pest, _Phylloxera vastatrix_.
As a rule the animals die out very shortly after their arrival on
foreign soil. Many instances, nevertheless, are on record, especially in
the case of molluscs, where snails thus transported have not only
survived but are apparently in a flourishing condition and spreading.
_Helix aspersa_, for example, our large garden snail, has been
naturalised in many foreign countries by French and Portuguese sailors,
who had taken them on board their ships as food.
It certainly cannot be denied that a number of species among almost all
groups of invertebrates have been unintentionally conveyed by man from
Europe into foreign countries. It has been proposed by Dr. von Ihering
to apply the term "cenocosmic" to those species which have become spread
all over the world through artificial means, and thus to distinguish
them from cosmopolitan ones which have attained a similar range
naturally. The latter he calls "palincosmic" species (_a_, p. 422). Many
so-called cenocosmic ants are believed by Dr. von Ihering to be
palincosmic. We are altogether too apt to regard cosmopolitan as
synonymous with introduced, and we should hesitate before concluding
that because one of our common European species occurs in Australia or
South America, it must have been transported there recently by human
agency. Some of our widely-distributed forms are probably of very great
antiquity, and may have spread to distant lands in early Tertiary times,
when a different state of the geographical conditions enabled them to do
so.
I cannot quote a more appropriate instance than the molluscan fauna of
Madeira. No less than thirteen of the Madeiran snails are looked upon as
having been introduced from Europe by human agency, on the sole evidence
that these happen to be common European species. Yet the correctness of
this supposition must be questioned in face of the interesting
observation made by Darwin (p. 357), "that Madeira and the adjoining
islet of Porto Santo possess many distinct but representative species of
land-shells, some of which live in crevices of stone; and although large
quantities of stone are annually transported from Porto Santo to
Madeira, yet this latter island has not become colonised by the Porto
Santo species. Nevertheless, both islands have been colonised by
European land-shells, which no doubt had some advantage over the
indigenous species." Darwin, therefore, meets the evident anomaly by
suggesting that the European species are supposed to possess some
advantages as colonisers. But the true explanation appears to me to lie
in the supposition that the European land-shells found in the Madeiran
Islands are all, or for the greater part, ancient forms which survived
both there and on the continent, whilst the remainder of the forms
inhabiting these islands are either such as are now extinct in Europe,
or have become modified since their arrival there from the continent at
a time when extensive land-connections allowed a free migration by land.
The theory of accidental introductions is an extremely popular one. It
allows free scope to a host of speculations, and once the idea has taken
firm root that a certain species is introduced, especially among the
class of naturalists who by way of experiment are wont to create new
centres of dispersion in their own neighbourhood, evidence to the
contrary must be of the most convincing nature to shake the popular
belief. Thus, it is almost regarded as an established fact by
conchologists and others, that the fresh-water mussel (_Dreyssensia
polymorpha_) was introduced into England at the beginning of this
century. Though it has been proved that this species is quite unable to
live in pure sea-water, yet the view that it has been carried from the
Black Sea ports to this country attached to the bottom of ships is
maintained by many, whilst others incline to the theory that the shell
came with timber. But _Dreyssensia polymorpha_ was by no means always
confined to the Caspian and Black Sea areas; it occurs abundantly in the
lower continental boulder-clay (see p. 230), and no doubt it had at one
time a much wider geographical distribution. It appears to me possible,
that it was able to maintain itself in certain fresh-water lakes and
slow-flowing rivers in Northern Europe, from which it might have spread
since the introduction of canals into Europe at the beginning of the
century. As the larva of this fresh-water mussel is free-swimming, its
propagation is much favoured by canals. Quickly-flowing rivers are fatal
to its existence, since the delicate larvae are swept out to sea and
perish. Such an hypothesis as this is strengthened by the fact of its
recent discovery in a sandy layer fifteen feet below the present surface
under the streets of London in a deposit which probably, as Mr. Woodward
remarks (p. 8), was accumulated in the early days of the city's
existence. In spite of Mr. Woodward's interesting find, and Dr.
Jeffreys' opinion, who always maintained that this shell was indigenous
to England, popular belief still clings tenaciously to the introduction
theory.
Among man's intentional introductions into a new country, no instance is
better known than that of the rabbit to Australia. Rabbits are entirely
confined to Europe. In their transplantation to Australia they were
carried to a country with a different climate and among new
surroundings. Yet the rabbits flourished, and within comparatively few
years increased to such an extent as to become a burden and pest to the
country. It may be remembered though, that, owing to the complete
absence of small carnivores, which act with us as a check upon the too
rapid increase of this rodent, the speed with which it established
itself in the new surroundings is not so very surprising.
Many of the English settlers in the New World felt that America lacked
the presence of our familiar birds. The homely sparrow was therefore
brought over, with the result that the Agricultural Department of the
United States is now devising means for its destruction, so rapid has
been its increase.
Similarly, the inhabitants of Jamaica, annoyed by the great profusion of
rats in their island, sent over to India for a number of mongoose. These
have decimated the rats since their arrival, but they have multiplied to
such an extent as to be a serious menace to the native fauna.
To give an instance nearer home, the Capercaillie (_Tetrao urogallus_)
was successfully introduced into Scotland in 1837. From its different
centres of distribution it is spreading in all directions where
sufficient cover is obtainable. But this case differs from the others
very materially, in so far as this bird was formerly a native of
Scotland, and only became extinct during the last century.
However, although there are many examples of undoubtedly successful
introductions by human agency, quite as many, or perhaps more,
unsuccessful ones might be quoted. In fact, it is by no means easy to
establish a species in any new locality. Frequently it happens that the
species seems to be on the increase at first, but then there is a
decline, and after a few years the new plantation has entirely vanished.
In other cases, the species disappears immediately after the
introduction takes place, or lingers on for many years if it receives
special and uninterrupted protection.
It may not be generally known that the English Hare (_Lepus Europaeus_)
is not found in Ireland, where the Mountain Hare (_Lepus variabilis_)
alone occurs. Attempts to acclimatise the English species have been made
in a number of places in Ireland, but many of them have been failures,
and not one of them has been a signal success.[4] Similarly, the
endeavour to introduce the French or Red-legged Partridge (_Caccabis
rufa_) into Ireland has met with a like result. According to Dr. Day, it
was tried during the summer of 1869 to naturalise the Sterlet
(_Acipenser ruthenus_) from Russian waters into the Duke of Sutherland's
River Fleet by importing artificially impregnated ova. From one hundred
and fifty to two hundred lively young sterlets are said to have been
turned out, but nevertheless the experiment met with no success. Several
fortunately abortive efforts were also made in British rivers to
establish _Silurus glanis_, a hideous monster of a fish, and quite
unpalatable.
The Natterjack Toad (_Bufo calamita_) has a very local distribution in
the British Islands. In Ireland it is found only along the coast of
Dingle Bay in County Kerry, where it is known among the peasantry as the
Black Frog. There is no doubt about its being indigenous there, and
though it has not spread beyond the very limited area of its habitat,
the Irish climate cannot be said to be unsuited to its existence. Yet it
seems to be extremely difficult to acclimatise it elsewhere, for though
no less than sixty specimens were turned out in Phoenix Park, Dublin,
about forty years ago, none of them were ever seen afterwards. They were
placed in the vicinity of one of the lakes, so as to give them ample
scope for breeding and developing the young, and in surroundings which
were considered eminently suitable at the time.
It has occasionally happened, too, that animals are introduced by
kindly-disposed persons with the view of adding a species to their
fauna, in complete ignorance of their previous existence in the country
where they wished to naturalise them. Thus we are told that in the year
1699 one of the Fellows of Trinity College, Dublin, procured Frog's
spawn from England in order to add that amphibian to the Irish fauna. It
was placed in a ditch in the College Park, whence the species is
supposed to have gradually spread all over the island. This story is
quoted by many writers as the true history of the Frog in Ireland, and
is given as an example of the rapidity with which animals spread.
Unfortunately the would-be introducer seemed unaware that, according to
Stuart's _History of Armagh_, the first Frog which was ever seen in
Ireland made its appearance in a pasture field near Waterford about the
year 1630, that is to say, seventy years before its introduction in
Dublin.[5] But even Stuart was mistaken in supposing that no Frog had
ever been seen in Ireland before, since Giraldus Cambrensis, in his
_Topography of Ireland_, mentions that a Frog was found in a meadow near
Waterford in the year 1187.
Certain British species of vertebrates are generally looked upon as
introduced species, though we cannot trace any record of their first
establishment, and it is quite possible that, though there was local
extinction and subsequent local re-introduction, they are truly
indigenous and may never have become totally extinct. Such are, for
instance, the Rabbit (_Lepus cuniculus_) and the Pheasant (_Phasianus
colchicus_). The latter certainly had become naturalised in England
before the Norman invasion.
But cases of introduction such as those above referred to are by no
means confined to the vertebrates, similar instances among invertebrates
being numerous enough. I am sure every naturalist is personally
acquainted with a good number, and it is hardly necessary that I should
quote in any detail after what has been said on the subject generally.
The two species of snails, _Helix pomatia_ and _Cyclostoma elegans_,
both of which occur in England, and which I had occasion to mention
among those experimented on by Darwin, were turned out in several
suitable localities in Ireland by Thompson, but failed to establish
themselves. The former, according to Mr. Kew, was also introduced into
Scotland and Norway, whilst fifty or sixty specimens were brought to
Petersfield in England, but none of these trials at acclimatisation were
successful. As among vertebrates, a large number of the so-called
successful introductions rest upon insufficient evidence.
When we once more carefully review the evidence as to the undoubted
difficulty attendant on intentional introduction of animals by human
agency, placed as they often were in most suitable localities, we must
feel that accidental introduction cannot play an important role in the
making of the fauna of any country. Especially is this the case with an
island fauna. Vertebrates are almost altogether excluded, and
invertebrates must arrive singly as a rule, often stranded on an
inhospitable and unsuitable shore. Their chances of surviving a passage
by sea, of finding suitable food and shelter and a mate in order to
procreate their species, appear to me infinitesimally small. Yet there
may be some such cases. However, I quite agree with Mr. Andrew Murray--a
high authority on geographical distribution--that "colonisation or
occasional dispersal is insufficient to account for the character of
the faunas and floras of oceanic islands; and I believe that the normal
mode in which islands have been peopled, has been by direct continuity
with the land at some former period, or by contiguity so close as to be
equivalent to junction" (p. 15). "That a slight intermixture," he
continues, "due to Mr. Darwin's colonisation, occurs in many (probably
in all) I am ready to admit; and from instances to be afterwards
noticed, I am disposed to reckon the proportions of such intermixtures
in the flora, in the most favourable circumstances, at not more than two
per cent. In the fauna I think it must be much less."
Mr. Murray's views, though they relate only to oceanic islands, are
likewise applicable to continental islands such as our own. I think we
might take the admixture in the British fauna due to occasional,
including human introduction, as amounting to five per cent. It is
better to take a high estimate, so as to include all the species about
whose native land there might be some reasonable doubt. Now of what
importance, after all, is this five per cent.? The remaining ninety-five
per cent. of the species of animals belonging to the British fauna
undoubtedly migrated to these islands in the normal way by land.
It is of great importance, in dealing with the question of the origin of
the British fauna, to thoroughly grasp this conclusion--_that
ninety-five per cent. of the animals have reached us by land_. We can
afford in fact to ignore the five per cent. altogether. It is an
insignificant factor. As regards the botanical aspect of the question,
botanists are quite in accord with the zoologists, and entirely share
their views in the belief of a former land-continuity between the
British Islands and the Continent. "It cannot be denied," says Professor
Blytt (p. 32), "that a plant of one or another species may, in an
exceptional case, migrate, without human assistance, all at once, across
large tracts of land and sea, and that such migration, if operating
during geological periods, might introduce a number of species even into
distant oceanic islands; but when the question is of whole communities
of plants, such as the above enumerated elements in our flora, then such
an accidental and sudden transport across large tracts can only be
conceived to be at all probable in the case of Arctic plants carried by
drifting ice to a bare country without native flora; as to the other
species, we must imagine that the _migration during the gradual change
of climate has proceeded slowly and step by step across connected tracts
of country_. In that manner we may assume that our country has in the
course of time obtained its present covering of plants. Each of the
above-named elements in our flora has doubtless its corresponding
element in our fauna. The fauna and flora of a region stand in relation
of complicated dependence to each other. The animals live on the plants.
The fecundation of the plants takes place in a great degree by means of
insects; their seeds are often scattered by resident birds and
quadrupeds. Everything indicates that _conveyance to small distances is
the rule_, and that sudden and long migration is the exception."
The conviction which has been gained by zoologists and botanists, that
the British Islands once formed part of the Continent, is based on the
present British fauna and flora. The remains, however, of animals which
used formerly to live in these countries, such as the Mammoth, the Irish
Elk, the Cave Bear, and many others, tell us the same tale. They could
not have peopled England by swimming across the Channel, or even by
walking across solid ice, as has once been suggested. Nothing but a
land-connection induced them to explore this country more closely, and
finally to decide on settling there.
The origin of the British fauna will be discussed more in detail in the
third chapter. The methods of investigation adopted, along with a
general scheme of this book, will be found in the next.
The manner in which the origin of the fauna of any particular
continental area can be traced is very similar to that adopted in the
case of an island. Portions of the continent of Europe can be shown to
have been islands in former times. Thus the Crimea, now a peninsula
united to the mainland by the narrow isthmus of Perekop, must have been
an island in comparatively recent times. The absence of a number of
striking and familiar South Russian species of mammals and reptiles
proves this to have been the case. It was probably long after the
appearance of man, though before historic times, that these changes
took place.
We shall learn in the subsequent chapters, that by a careful study of
the fauna and flora the fact can be established, not only of the former
connection of an island with a continent, but also whether such union
existed (geologically speaking) within recent or more remote times. The
better the fauna is known, both recent and fossil, the more precisely
can the period of connection be indicated, and its duration determined.
FOOTNOTES:
[1] The numbers in brackets throughout this work refer to the
page-number in the Bibliography at the end.
[2] A map giving its exact distribution in Ireland will be found on p.
300, and a figure of the slug on p. 298.
[3] The term _endemic_ will be employed throughout this work as applied
to species peculiar to a country and not found elsewhere.
_Autochthonous_ will be used in speaking of a species which has
originated in a country to which, however, it is not peculiar; _e.g._,
the Chamois is an autochthonous Alpine species, but occurs also in the
Pyrenees and Caucasus. An _indigenous_ species is one native to a
country, as opposed to the term "introduced," and is applicable to all
species which have reached it by ordinary migration.
[4] I might refer any one more specially interested in these
introductions to an article on this subject in the _Irish Naturalist_ of
March 1898, by Mr. Barrett-Hamilton.
[5] I should recommend those who are particularly interested in the full
history of the Irish frog to read the notes on this subject contained in
vol. ii. of the _Irish Naturalist_.