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Without a classification, it is impossible to scientifically study any natural object. Organisms not only need names, but they need categories to convey meaning. Finding myself in the middle of the North American forest, my friend warned me from afar, “Watch out for the poison ivy!” I knew what ivy was, but how could you tell normal ivy from poison ivy? He could list a set of characteristics that diagnose poison ivy. I am not a botanist so these characteristics would be meaningless; moreover, I would need to touch the poison ivy in order to identity it. “It looks green!” came the reply. My friend was not a botanist either, so I was to avoid a green type of ivy, which I assumed was of a climbing variety. This basic form of communication is helpful to avoid danger or useful to discriminate an edible berry from the one which is toxic. Communication is an essential part of scientific practice as well as its goal. The first question any taxonomists would ask is “What is this?” followed by “What are its characteristics?” and then “What is it most like?” The same is true when we deal with the distributions of animals and plants. Kangaroos do not come from “over there”. They have a particular place in the world, which is determined through a hierarchical classification:

Earth

Southern Hemisphere

Australia

There was also an understanding of a basic classification with the poison ivy:

Plant

Ivy

Green

While this is a basic classifications, it works in communicating information and meaning. In order for the classification to work, biogeographers need to be able to communicate plant and animal distributions clearly, either as a list, table or map. A distribution map simply lists where certain organisms occur. Zimmermann (1777) published the first modern distribution map (Figure 1.1) in which the global distributions of terrestrial quadrupeds are named in the areas where they occur. Note that the hierarchy is purely geographical:

Old World

Europe

Africa

Asia

New World

North America

South America

Australasia

Zimmermann’s map was accompanied by a 600-odd page treatise that described the distributions in four chapters:

Chapter I: Animals dispersed throughout the world and their degeneration

Chapter II: Introduction

Part One. Quadrupeds of both the Old and New World

Part the Latter: Quadrupeds of the Old World

Chapter III. Quadrupeds of the New World

Chapter IV. In which the animals are generally treated by the dispersion across the surface, whose consequences are added in the history of the planet (Zimmermann 1777, p. xxiv)

Figure 1.1. Zimmermann’s Tabula mundi geographico zoologica sistems quadrupedes hucusque notos sedibus suis adscriptos, second edition of 1783. Source: National Library of Australia. For a color version of this figure, see www.iste.co.uk/guilbert/biogeography.zip

Although Zimmermann’s zoogeographical classification is basic, it does serve a purpose – to explain distribution and dispersal of quadrupeds. Compare the first of these zoogeographical classifications with a more recent bioregionalization by Morrone (2015, Figure 1.2):

Holarctic kingdom

Nearctic region

Palearctic region

Holotropical kingdom

Neotropical region

Ethiopian region

Oriental region

Austral kingdom

Cape region

Andean region

Australian region

Antarctic region

Figure 1.2. The biogeographic regions of Morrone (2015). Areas in yellow are part of the Holarctic kingdom: 1. Nearctic region; 2. Palearctic region. Areas in red are part of the Holotropical kingdom: 3. Neotropical region, 4. Ethiopian region, 5. Oriental region. Areas in blue are part of the Austral kingdom: 6. Andean region 7. Cape region, 8. Australian region, 9. Antarctic region. Areas in orange and purple are transition zones: 10. Mexican, 11. Saharo-Arabian, 12. Chinese, 13. Andean, 14. Indo-Malayan (Wallacea) (Escalante and Morrone 2020, p. 12, Figure 1.2) For a color version of this figure, see www.iste.co.uk/guilbert/biogeography.zip

The areas of Morrone (2015) serve a different purpose, namely to be able to study the relationships of these areas. In fact, Zimmermann’s and Morrone approaches are completely different methodologically, theoretically and historically; yet, both need a classification in order to be able to communicate their ideas to other plant and animal geographers. In other words, it is impossible to do animal and plant geography without a classification. Classifications, however, do not necessarily overlap as in the case of Zimmermann and Morrone. The classification of Zimmermann is based on the geographical regions of the world in the 18th century (note that Antarctica is missing in the former), while that of Morrone has its historical roots in both the zoogeographic Sclater–Wallacean and phytogeographic Humboldtian tradition. But where Zimmermann and Morrone do overlap is that they use the distributions of named species.

One of the many benefits of doing plant and animal geographies, both in the 18th and 21st centuries, is that plant and animal distributions are available in the form of a database. Zimmermann had access to the many travelogues of explorers of his day such as James Cook, Louis Lahontan and Jan Struys, whereas Morrone had access to recent biogeographical classification (i.e. regionalizations) that had used publicly available digital distribution databases such as GBIF. Practically, these two approaches are the same. They are time and cost-effective (neither had to go into the field and collect and describe new species) and they are quick to access (both had access to libraries of one sort or another). Many plant and animal area classifications during the 18th and 19th were collated via the literature (e.g. Stromeyer 1800; Pritchard 1826). But what if you had the funds to go to an area that was poorly understood and under-collected? What if you had the funds to collect plant specimens and other data? How would you classify the natural history of an area? Alexander von Humboldt faced this problem during his journey to New Granada in present-day Colombia during the late 18th century and solved it in a most ingenious way.