William Swainson, William Kirby and William Spence were insistent on the necessity of defining natural regions, namely “those grand divisions of animal geography pointed out by nature, and immediately recognized by every naturalist” (Swainson 1835, p. 11). Swainson places William Sharp Macleay and Humboldt among those who recognize that natural areas are not “regulated by isothermal lines” (Swainson 1835, p. 12). The famous Tableau Physique of Humboldt, depicting mounts Chimborazo and Cotopaxi in the Andes, were drawn in cross-section in order to highlight isothermal lines4 (Figure 1.4). We can imagine that Swainson considered all lines, be they isothermal lines or latitudinal lines, as artificial. Yet, isothermal lines were quite popular with plant and animal geographers in delimiting climatic zones. Given, however, that climate and plant forms define vegetation, we could argue that the Humboldtians would consider such lines to portray natural areas. After all “only those vegetative formations deserve to be recognised as independent plant forms, which conform to the influence of climate” (Grisebach 1866, p. 384).
Figure 1.4. Humboldt’s Tableau physique showing a cross-section of Mount Chimborazo and Mount Cotopaxi in the Andes. The full title of the map reads: Geographie des plantes equinoxiales : tableau physique des Andes et Pays voisins. Dressé d’après des observations et des Mesures prises sur les lieux depuis le 10.degré de l’attitude australe en 1799, 1800, 1801, 1802 et 1803 (in Humboldt and Bonpland 1807) (source: http://cybergeo.revues.org/docannexe/image/25478/img-7.jpg). For a color version of this figure, see www.iste.co.uk/guilbert/biogeography.zip
While some zoologists would adopt a more Humboldtian approach to delimiting areas using climate, such as the homoiozoic belts of Forbes (1856) or the life zones of Merrian (1892), others sought to look only at the distribution of species. An earlier attempt at using animal distributions to define animal regions was proposed by Johann Karl Wilhelm Illiger in 1815. Illiger (1815) attempted to summarize the global geographical distribution of mammals by counting the number of species that occurred in each continent. Much of Illiger (1815) are tables listing the names of genera, families and orders and the numbers of species found in each continent. The work is completely taxonomic, devoid of any measurements of temperature or rainfall, and synthetic, as it had collated names of species from the works of others. The body of work is divided into sections or “comparative summaries” based on each of the tables, including a description of the faunal distribution of a list of the taxa. A modern-day biogeographer would be impressed with the volume of data but perplexed with how little Illiger had done with it. German paleontologist Johann Andreas Wagner synthesized Illiger (1815) into four mammalian provinces in a three-part work published between 1844 and 1846 (Wagner 1844–1846). The work also included the first known global biogeographic map (Figure 1.5). Wagner was also the first to use a hierarchical classification of zones, provinces, sub-provinces and regions (Table 1.1). More important, Wagner considered these divisions to be natural. In staying with Illiger’s style of only listing the distributions of mammals, Wagner stands out in zoological and botanical geography by ignoring abiotic factors such as climate. Wagner’s contemporary Ludwig Schmarda’s Distribution of Animals (Schmarda 1853), for example, discusses the influence of climate, water and temperature, as well as denoting “tropical forms” and the interaction with vegetation. Schmarda’s map of the geographical distribution of animals is possibly the most detailed of any zoogeographical study in the 19th century. The map depicts 21 terrestrial and 10 oceanic areas and the distributions of various taxa, as well as the location of reefs, atolls, the direction of ocean currents, isothermal lines and latitude and longitude. Unlike Wagner’s classification, Schmarda’s was non-hierarchical and partially based on climate. Unfortunately, Wagner’s work was largely ignored and those who did notice it never quite fully appreciated its significance. The nearest zoogeographical work to resemble Wagner’s appeared a decade later. Philip Lutley Sclater, who used a similar method to Wagner, namely counting taxa, proposed a hierarchical classification. Sclater, however, offered something new:
In the Physical Atlases lately published, which have deservedly attracted no small share of attention on the part of the public, too little regard appears to have been paid to the fact that the divisions of the earth’s surface usually employed are not always those which we most natural when their respective Faunæ and Flora are taken into consideration. The world is mapped out into so many portions, according to latitude and longitude, and an attempt is made to give the principal distinguishing characteristics of the Fauna and Flora of each of these divisions; but little or no attention is given to the fact that two or more of these geographical divisions may have much closer relations to each other than to any third, and, due regard being paid to the general aspect of their Zoology and Botany, only form one natural province or kingdom (as it may perhaps be termed), equivalent in value to that third (Sclater 1858, pp. 130–131).
Figure 1.5. “Representation of the distribution of mammals according to their zones and their provinces. The southern boundary of the northern polar province is indicated by a line of a different color, drawn somewhat further south than the equatorial border of the arctic fox ([Vulpes] lagopus), though not so far in some places as the reindeer may descend there on their summer migrations. The southern polar province is not included in this map, because it is only in the process of discovery and, according to all previous experience, it does not harbour land mammals” (Wagner 1844, 241, Table 1.1). For a color version of this figure, see www.iste.co.uk/guilbert/biogeography.zip
Table 1.1. The hierarchical classification of zones, provinces, sub-provinces and regions listed in Wagner (1844–1846). Note that Wagner considered a third Southern Polar province, but omitted it partly because “we know too little about it and partly since it has no land-animals, and the marine mammals for the most part the same ones are found on the coasts of South America, South Africa, and Australia” (Wagner 1844, p. 86)
| Zone | Province | Sub-Province | Region |
|---|---|---|---|
| Northern | Polar | Europe | |
| Nowaja Semlja | |||
| Siberia | |||
| America | |||
| Greenland | |||
| Old World | a. Middle Europa | ||
| b. South Siberia | |||
| c. Binnenmeerisches Steppes | |||
| d. Mediterranean Basin | |||
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