It is possible that further investigation will show that not the mammals only, but land animals in general can be grouped according to their habitat like plants, but so far the attempts made in this direction have been tentative only. Generally, we may say that the mammals of Central Europe are of the woodland type, but no detailed classification into steppe and woodland animals exists. It may be useful, therefore, to indicate the chief kinds of mammals found in the European area, grouped according to affinity, in the absence of a geographical classification.
Mammals, apart from the egg-laying monotremes, and the marsupials of Australia, are divided into nine orders, and of these, one, that including the anteaters, etc., of South America, Africa and India, is entirely unrepresented in Europe. Another, the Cetaceans, or whales, has no land representatives; and the same is true of the aberrant sea-cows, though their ancestors lived on land and occurred in Egypt.
Excluding these orders we are left with six which have European representatives. These are the following:--
Insectivores, or insect-eating mammals, such as moles, shrews and hedgehogs.
Ungulates, or hoofed animals, including horses, cattle, sheep, deer, pigs, etc.
Carnivores, or flesh-eaters, including lions, cats, foxes, dogs, etc.
Rodents, or gnawing animals, among which are rats, mice, squirrels, etc.
The _Primates_ are represented by one form only, the Barbary ape, found in Gibraltar. _Bats_ are numerous, but are of less geographical interest than land forms. The remaining four orders are all important. The _Ungulates_ include the largest land mammals, and their size and conspicuous nature have led to the gradual replacement of the wild forms by domesticated ones. Only a very few, such as deer, wild goats (ibex), the wild boar, the wild sheep (moufflon) of Corsica, manage to survive, and that mostly by aid of special protection. The presence of the large wild forms is incompatible with almost any form of agriculture as is often proved disastrously in Africa, hence man's ruthless warfare upon them.
But if man has destroyed the large ungulates he has found himself unable even to reduce the numbers of the _Rodents_, who gain in many ways by civilisation. The destruction of their rivals, the grass-eating ungulates, increases their natural food-supply. In South America, where there were very few ungulates till the white man brought his flocks and herds, the rodents were very numerous and reached a great size. Again, the operations of agriculture give the rodents enormous artificial sources of food-supply, and the number of man's domesticated or semi-domesticated animals makes him wage a bitter war against the small carnivores, the natural enemies of the rodents. Protected from their enemies, abundantly fed by man's providence, it is no wonder that these small animals have multiplied greatly.