ABSTRACT
The conditions defining the “stations” of a species vary. They depend not only on physical factors but also on the plant and animal populations present in a given region. The geographical expansion of one species modifies the conditions of existence of others. The devastating impact of the eruption of the polar bear into Iceland is described: the population equilibria of plants and animals were permanently disturbed. The consequences of the first appearance of an animal are also examined. They are considered to be especially important up until the time when an equilibrium is reestablished, which might be several centuries. The question of the influence of man on living nature is then discussed. The first point is whether man increases the productive forces of the earth. This is a complex question: in a given area, vegetation may become less abundant, but may acquire much more importance agriculturally. Man tends to reduce the natural diversity of animal and plant stations and to reduce them to a small number suitable to species considered useful. The growth of the human population has thus caused the extinction of species (like the Dodo) or dramatic reductions in their numbers.
In contrast, domestic quadrupeds (cattle, horses and pigs, in particular) have rapidly propagated on the American continent. This is also the case of reindeer brought into Iceland. It follows that the worldwide population constitutes only a small portion of what the planet could feed. Nonetheless, mankind is not alone in having the power to destroy species: every species imposes itself to the detriment of some other species. The many changes going on today should be considered as reflections of the uniformity of this system over time, according to a principle of eternal variation.
