1.3. Ecology versus taxonomy: populations not species
The “two courses” of plant classification did not sit well with early ecologists. Linnaean taxonomy and species were considered to be arbitrary and artificial, while vegetations and plant forms were considered to be natural. Ecologists Eugenius Warming, Andreas Schimper, Frederic Clements and Henry Chandler Cowles were incredibly wary of taxonomic description, something Clements (1905, p. 11) decried as “vague descriptive articles” (Hagen 1986). Cowles warned:
Taxonomy must be scientific. It must require for its devotees a training as rigid as that required by professional workers in morphology, physiology or ecology. Species-making by taxonomic tyros must be abandoned … These things will not, be endured much longer; a little more and the sinning taxonomists will be cast out into the outer darkness where there shall be wailing and gnashing of teeth (Cowles 1908, pp. 270–271).
Were ecologists truly enraged with taxonomy, or were they after recognition for their newly developing field? Hagen (1986) proposed that early ecologists such as Clements were attempting to legitimize their discipline by distancing it from amateur botany “and to place it on a credible scientific basis” (Hagen 1986, p. 200). One way to draw attention to this is by defining their “new discipline in opposition to what they believed was a moribund, nineteenth-century, natural-history tradition” (Hagen 1986, p. 213). The move towards communities of plant forms, rather than species, was not unique to early 20th century ecologists. Neither was the notion that descriptive taxonomy and zoogeography were static and moribund. Species are essentially hypothetical, in the sense that a set of diagnostic characteristics are given a name and assigned to various types. Organisms that show these diagnostic characteristics are then assigned that name. Plant or life forms, however, were based on the traits of a community or a population. Moreover, populations were observable, that is, quantifiable, rather than abstract in the way species are defined. Populations changed over time, as they evolved new traits, and showed new adaptations. Populations would form faunal elements, thereby relinquishing the need for formal areas. You can have Old World elements in the New World, populations that disperse and establish themselves as new populations in new areas. Populations could also form refuges in cases of changes in climate or landscape, such as advancing ice caps. At the population level, so many more current geographic and climatic events can be used to explain the distribution of populations. Yet, the area classification remained; only the way plant and animal geographers define their areas varied. Mayr, who thought the Sclater–Wallacean areas were static, “descriptive, essentially regional, and non-dynamic” (Mayr 1946, p. 4), proposed a “Classification of faunal elements of the Americas” (Mayr 1946, p. 11), in which the elements were defined as “Old World”, “Holarctic” and “Pantropical”. These are the same static areas Mayr denounced earlier in the same paper. The only difference is that the subregions are treated as “faunal elements”, that is, populations, which are assumed to have dispersed between the larger regions.
Plant communities, populations or faunal elements are simply ways in which we describe the smallest unit of classification. We may speak of a population of koalas, but koalas (Phascolarctos cinereus) have to be identified through a unique or diagnostic set of characteristics. Koalas are diprotodontids and share the characteristics of other diprotodontids, such as kangaroos. Kangaroos and koalas are marsupials, such as the American opossum, and kangaroos, koalas and opossums are mammals. Without such a classification, we would not be able to identify a population or various individuals within a community. The “two courses”, namely vegetation and species (flora) classifications, which were so prevalent in plant geography and classification during the early 20th century, did unify by the 1940s. In 1947, Ronald Good proposed a “classification of the world into floristic units” (Good 1965, pp. 30–32), which was updated by Takhtajan et al. (1986). The hierarchical classification, divided up into kingdoms, subkingdoms and regions and subregions, is reminiscent of the Sclater–Wallacean regions (i.e. Neotropical, Indo-Malaysian, Australian). The smaller subregions are based on climate (e.g. Central Deserts) or geopolitical or geographical areas (e.g. Borneo, Mexican Highlands) and seem to resemble plant communities. Good seems to have combined the larger regions with the smaller plant communities into a single classification. In zoogeography, the Scalterian–Wallacean regions prevailed into the 21st century. Early objections to a “static” area classification never challenged how the classification functions, but rather how areas are defined. Ortmann (1902) was very particular on how areas should be defined:
1) Any division of the earth’s surface into zoogeographical regions which starts exclusively from the present distribution of animals, without considering its origin, must be unsatisfactory, since always only certain cases can be taken in while others remain outside of this scheme.
2) Considering the geological development of the distribution of animals, we must pronounce it impossible to create any scheme whatever that covers all cases.
3) Under these circumstances it is incorrect to regard the creation of a scheme of animal distribution as an important feature or purpose of zoogeographical research (Ortmann 1902, pp. 269–270).
There are multiple ways to define areas; however, no one method can claim that it finds natural areas; this is simply assumed. Regardless of how we define areas, an area classification is always needed in order to communicate what it is we are trying to convey.
The Sclater–Wallacean areas are still in use today, and various authors using geospatial methods have identified similar classifications to that of Sclater and Wallace (Figure 1.6) using different models (Kreft and Jetz 2010; Proches and Ramdhani 2012; Holt et al. 2013; Figures 1.7–1.9). If we look at these three different studies using different data, methods and theories, we find that the same Sclaterian–Wallacean areas keep appearing. While these approaches have different origins in their ideas and methods, the practice of looking at and proposing area classification has not changed since (Zimmermann 1777).
Figure 1.6. “Map of the World, showing the Zoo-Geographical Regions and the contour of the Ocean-bed” (Wallace 1876, frontispiece). For a color version of this figure, see www.iste.co.uk/guilbert/biogeography.zip
Let’s return to Goethe’s observation that “the history of science is science itself”. In the case of area classification, we see that biogeographers keep doing the same thing, proposing area classifications, but using very different and independent approaches. If we look at scientific theories and methodologies, we find multiple origins in biogeography. But biogeographic practice, namely area classification, seems to constantly reinvent itself. The history of science is truly science itself.
Figure 1.7. “The six major biogeographical divisions are highlighted in the dendrogram with large coloured rectangles: orange, Australian; red, Neotropical; brown, African; yellow, Oriental; blue, Palaearctic; green, Nearctic. The first 30 groups in the dendrogram (small rectangles) and in the map are displayed in different colours. Additionally, the first 60 groups are indicated with black boundaries in the map” (Kreft and Jetz 2010, Figure 1.9). For a color version of this figure, see www.iste.co.uk/guilbert/biogeography.zip
Figure 1.8. Vertebrate zoogeographical regions and subregions (Proches and Ramdhani 2012, Figure 1.2). For a color version of this figure, see www.iste.co.uk/guilbert/biogeography.zip
