53 (4) • November 2004: 889–891 Ebach • Forum on biogeography: introduction FORUM ON BIOGEOGRAPHY: INTRODUCTION Malte C. Ebach Forum Editor Department of Botany, The Natural History Museum, Cromwell Road, London SW7 5BC U.K. male@nhm. ac.uk The process of unifying biogeography has had its Malte C. Ebach poor fossil record. The cladis- many champions. Originally, in pre-evolutionary tic revolution in systematics Europe, biogeography was unified by the common aim also highlighted the need for of uncovering the centre of origin, a concept derived monophyletic groups in order from biblical texts. Organisms either were created in the to discover historical patterns places they were found or they moved there from else- of taxa (Williams & Ebach, where (Buffon, 1766; Sclater, 1858). Whether or not the 2004). Biogeography under organisms evolved was not an issue in biogeography. the Croizatian unification was Organisms had a centre of origin (either by creation or historical and focused on dis- evolution) from which they moved, thus forming the covering patterns and then strange distribution patterns both in living and fossil explaining them. Discovery species. The advent of Darwinian evolutionary theory, a for some, however, is not separate from explanation or process (natural selection) proposed to explain biogeo- mechanical processes (see Hull, 1988). graphical distribution, was seen to be a unifying theme. Proponents of phylogenetic systematics are con- Organisms had one centre of origin. Ernst Haeckel, who vinced that transformational optimizations in phyloge- was deeply influenced by Darwin’s work, proposed a netic trees offer the best way to approach biogeography. centre of origin for mankind. At first he believed it was All phylogenetic lineages have separate centres of origin the lost island of Lemuria, sunk off the coast of Pakistan. which by way of discovery, offer a better explanation for In a later revision he moved it to present day Afghanistan distributions and diversity. Recently, Brooks (in press) (see Haeckel, 1876). Earth at this time was thought to be and Donoghue & Moore (2003) have argued that Life static, continents were set rigid and only oceans and cli- and Earth, in fact, do not evolve together, thus leaving mate were seen to be dynamic. The unifying theme of the pursuit of centres of origin and direction of dispersal biogeography relied on the actions of ocean currents and once again open for debate. Naturally each author realis- climate to explain odd distributions of living and fossil es the impact of a dynamic Earth, but not as the main aim taxa. Matthew (1915), Darlington (1957), Simpson of biogeography. (1965) and MacArthur & Wilson (1967) were champions A similar reaction had occurred in molecular sys- of static Earth biogeography, a theme united by disper- tematics. The advent of molecular data in systematics sals and centres of origin. But unity did not last long. and its eventual focus on biogeography is the next and The discovery of diverging plate margins after the latest unification in biogeography. All unifications before Second World War was the final clinching argument for were based on morphological data and aimed at species continental drift and a dynamic Earth (see Hess, 1962). level and above. Molecular data in biogeography, cham- The works of Taylor (1910), Wegner (1915), du Toit pioned by phenetists such as Sokal (1979), were con- (1937) and Carey (1976) finally came to the forefront. cerned with comparing genetic with geographical dis- The role of continental drift explained disjunct fossil dis- tance. Unification came in the form of the most accurate tributions, but more importantly it highlighted the speed measurement for genetic distance and genetic relation- at which plates could move and topology could change. ships. Phylogeography is now the leading molecular bio- Léon Croizat was the first to champion the idea that Life geographical theory. and Earth evolved together as a unifying theme for bio- The island biogeographers stemming from Mac- geography (Croizat, 1958, 1964). Donn Rosen (1978), Arthur & Wilson (1967) relied on unification via statisti- Gareth Nelson, Norman Platnick (see Nelson & Platnick, cal measurement of diversity and proposing accurate 1981), Robin Craw, Michael Heads and John Grehan models with which to predict future and past distribu- (see Craw & al., 1999) developed Croizat’s ideas further. tions. The dynamic Earth had little effect on island bio- The search for centres of origin was a task that no longer geography, as it is still mostly concerned with ecology, or unified biogeography. Earth was dynamic, older areas simply biological interactions. Walter (2004) states that were impossible to find, and many living species had a unification can be achieved by integrating “all available 889 Ebach • Forum on biogeography: introduction 53 (4) • November 2004: 889–891 historic and present biogeographic information for the active and dynamic areas. development of predictive distribution models” (Walter, 2004). Unification in biogeography exists in three different states: LITERATURE CITED 1. Unification as life and Earth evolving together. Avise, J. C. 2004. What is the field of biogeography, and where 2. Unification as the most appropriate method. is it going? Taxon 53: 893–898. 3. Unification as a relevant model. Brooks, D. R. In press. Reticulations in historical biogeogra- phy: the triumph of time over space in evolution. In: Biogeography as one independent field is unified in Lomolino, M. & Heaney, L. R.(eds.), The Foundations of three different ways by the proponents of integrated Biogeography. Sinauer Associates, Sunderland, fields. An ecologist is more likely to be an island bio- Massachusetts. geographer, a molecular systematist a phylogeographer Buffon, C. de. 1766. Histoire Naturelle Generale et and a morphologist a historical biogeographer. These Particuliere, vol. 14. Imprimerie Royale, Paris. associations are not exclusive but rather highlight the Carey, S. W. 1976. The Expanding Earth. Elsevier, areas from which the calls for unification originate. Amsterdam. Craw, R. C., Grehan, J. R. & Heads, M. 1999. Panbiogeo- Unification is not an easy task for biogeography. The graphy: Tracking the History of Life. Oxford Univ. Press, different answers given by Avise, Parenti and Oxford. Humphries, and Walter in this forum, highlight the vari- Croizat, L. 1958. Panbiogeography. Published by the author, ous affinities of biogeographers. The question of unifica- Caracas. tion, however, still remains open. Do we return to Croizat, L. 1964. Space, Time, Form: the Biological Synthesis. Darlington and Matthew and find centres of origin and Published by the author, Caracas. explain pathways of dispersal unified by a method (sensu Darlington, P. J., Jr. 1957. Zoogeography: The Geographical Distribution of Animals. John Wiley and Sons, New York. Lieberman, 2003)? Can we continue to unify an integrat- Donoghue, M. J. & Moore, B. R. 2003. Toward an integrative ed field of ecology, genetics, geology and history by historical biogeography. Integr. Comp. Biol. 43: 261–270. uncovering patterns caused by a dynamic Earth? Are we du Toit, A. L. 1937. Our Wandering Continents: An Hypothesis bound to find one universal statistical model that unifies of Continental Drifting. Oliver and Boyd Ltd., London and biotic distribution (see Hubbell, 2001)? Edinburgh. Biogeography is an historical science, but at the Haeckel, E. 1876. The History of Creation, or, the Develop- same time is shaped by history. The path we as biogeog- ment of the Earth and its Inhabitants by the Action of Natural Causes: Doctrine of Evolution in General, and of raphers or as students in biogeography choose now will that of Darwin, Goethe, and Lamarck in particular (from influence decisions and the way we do biogeography in the German of Ernst Haeckel, the translation revised by E. the future. Unification will also be challenged and bear Ray Lankester), 2 vols. Henry S. King, London. its champions. In order for us to know how biogeography Hess, H. H. 1962. History of Ocean Basins. Pp. 599–620 in: is to be unified and where it will progress lies in our abil- Engel, A. E., James, J. H. L. & Leonard, B. F. (eds.), ity to understand its past. Petrologic Studies: A Volume in Honour of A. F. The purpose of this Forum is to analyze biogeogra- Buddington. Geological Society of America, Colorado. Hubbell, S. P. 2001. The Unified Theory of Biodiversity and phy for the researcher and student of biology, geography, Biogeography. Princeton Univ. Press, Princeton. and palaeontology currently faced with a daunting num- Hull, D. L. 1988. Science as a Process: An Evolutionary ber of theories and methods. It explores the wide range Account of the Social and Conceptual Development of of differing approaches to biogeography told in the Science. Univ. Chicago Press, Chicago. words of some of today’s leading biogeographers. Lieberman, B. S. 2003. Unifying theory and methodology in Biologists representing historical biogeography, island biogeography. Evol. Biol. 33: 1–25. biogeography and phylogeography, have been asked to MacArthur, R. H. & Wilson, E. 1967. The Theory of Island Biogeography. Princeton Univ. Press, Princeton. respond to four basic questions: Matthew, W. D. 1915. Climate and evolution. Ann. New York 1. How would you define biogeography and its goals? Acad. Sci. 24: 171–318. 2. Why are there so many biogeographical theories and Nelson, G. & Platnick, N. I. 1981. Systematics and methods? Biogeography; Cladistics and Vicariance. Columbia Univ. 3. In recent years there has been a call for the integra- Press, New York. tion or unification of biogeography. Do you think Parenti, L. R. & Humphries, C. J. 2004. Historical biogeog- this is necessary? raphy, the natural science. Taxon 53: 899–903. Rosen, D. E. 1978. Vicariant patterns and historical explana- 4. Has the use of molecular data changed the goals and tion in biogeography. Syst. Zool. 27: 159–188. therefore future development of biogeography? Sclater, P. L. 1858. On the general geographical distribution of The responses to these questions reveal that bio- the members of the class Aves.