National Geographic Magazine/Volume 1/Number 2/Geography of Life
REPORT—GEOGRAPHY OF LIFE.
C. Hart Merriam.
During the year now drawing to a close not a single work which I conceive to fall legitimately within the scope of the department of Geography of Life has appeared in any part of the world, so far as I am aware. It being manifestly impossible, then, to comply with the requirement of the By-law calling for a summary of the work of the year, I may be pardoned for digressing sufficiently to speak of what seems to be the function of this Society in its relations to biology.
The term 'Geography of Life,' applied without limitation or qualification to one of the five departments of the Society is not only comprehensive, but is susceptible of different if not diverse interpretations. Indeed, without great violence it might be construed to comprehend nearly the whole domain of systematic botany, zoology, and anthropology. As a matter of fact, I believe it was intended to include everything relating directly to the distribution of life on the earth. Thus it would naturally embrace all sources of information which assign localities to species. Local lists and faunal publications of every kind would fall under this head, and also the narratives of travelers who mention the animals and plants encountered in their journeys. In the single branch of ornithology, about fifty per cent. of the current literature would have to be included. The most obvious objection to this comprehensiveness of scope is the circumstance that a mere bibliographic record of titles alone would fill a journal the size of the National Geographic Magazine.
Hence it may not be amiss to attempt a preliminary reconnoissance, with a view to what my friend Mr. Marcus Baker has recently defined as "a Survey of Class II, for Jurisdictional purposes." Let us seek therefore to run a boundary line about the territory we may fairly claim without trenching on the possessions of others.
Before doing this it becomes necessary to bear in mind certain facts and laws without a knowledge of which it is impossible to think intelligently on the subject. It is a matter of common observation that different groups of animals and plants inhabit different regions, even in the same latitude; that some forms are almost world wide in distribution; that others are restricted to very limited areas; that the ranges of very dissimilar species are often geographically coincident; and that, as a rule, animals inhabiting contiguous areas are more nearly related than those inhabiting remote areas. The recognition of these facts early led to the attempt to divide the surface of the earth, according to its animal life, into 'faunal' districts. By the term fauna is meant the sum of the animal life of a region.
A comparatively meagre supply of information is sufficient to indicate the principal faunal subdivisions of a country, but for mapping the exact boundaries of such areas a vastly greater and more precise fund of knowledge is necessary. The way in which such maps are prepared is by collecting all available authentic records of localities where the particular species has been found. This is done by compiling published records, by examining labels of specimens in various museums and private collections, and by work in the field. The data thus brought together are arranged on cards under authors and regions, and are tabulated under species. The localities are then indicated by colored spots on an outline map, the space surrounded by the spots being washed in with a paler tint of the same color. A separate map is devoted to each species.
Faunal maps are made by combining a large number of species maps. In making such combinations it is found, as a rule, that a considerable percentage of the species maps fall into certain well defined categories whose color patches are essentially coincident. The composite resulting from the coördination of these maps may be held to represent the natural faunal areas of a country. Several such areas may be characterized by the common possession of species not found elsewhere, and may be combined to constitute a faunal province; several provinces, a region; and several regions a realm or primary zoö-geographical division of the earth's surface.
Having ascertained the actual extent and limitations of the natural faunal districts, it remains to correlate the facts of distribution with the facts of physiography.
My own convictions are that the work of this Society in Geographic Distribution should be restricted to the generalization of results: that we should deal with philosophic deduction rather than with detailed observations and the tedious steps and laborious methods by which they are made available. Our aim should be to correlate the distribution of animals and plants with the physiographic conditions which govern this distribution, and to formulate the laws which are operative in bringing about the results we see. In other words, we are to study cause and effect in the relations of physiography to biology.
The kind of works meriting discussion in the annual report of the Vice-president of this section are such philosophic treatises as those of Humboldt, Dana, Agassiz, DeCandolle, Engler, Darwin, Huxley, Pelzeln, Sclater, Wallace, Baird, Verrill, Allen, Cope, and Gill. As it is seldom that more than one or two such works appear in any single year, there is likely to be ample opportunity for profitable discussion.
January, 1889.