Historical Biogeography: Evolution in Time and Space

Evo Edu Outreach (2012) 5:555–568 DOI 10.1007/s12052-012-0421-2 GEOGRAPHY AND EVOLUTION Historical Biogeography: Evolution in Time and Space Isabel Sanmartín Published online: 21 June 2012 # Springer Science+Business Media, LLC 2012 Abstract Biogeography is the discipline of biology that Introduction studies the present and past distribution patterns of biological diversity and their underlying environmental and his- Thanks to advances such as better exploration techniques, torical causes. For most of its history, biogeography has satellite cartography, or the use of geographic information been divided into proponents of vicariance explanations, systems (GIS), global patterns of biodiversity distribution who defend that distribution patterns can mainly be are now fairly well understood. Conversely, the causal fac- explained by geological, tectonic-isolating events; and dis- tors and processes underlying such patterns are still debated. persalists, who argue that current distribution patterns are Biogeography is the discipline of biology that attempts to largely the result of recent migration events. This paper reconstruct the patterns of distribution of biological diversi- provides an overview of the evolution of the discipline from ty and to identify the processes that have shaped those methods focused on finding general patterns of distribution distributions over time. Why are organisms distributed (cladistic biogeography), to those that integrate biogeo- where they are today? How have faunas and floras assem- graphic processes (event-based biogeography), to modern bled through time? Traditionally, biogeography has been probabilistic approaches (parametric biogeography). The divided into two different approaches (Morrone and Crisci latter allows incorporating into biogeographic inference esti- 1995): ecological biogeography, the study of the environ- mates of the divergence time between lineages (usually mental factors shaping the distribution of individual organ- based on DNA sequences) and external sources of evidence, isms at local spatial scale, and historical biogeography, such as information on past climate and geography, the which aims to explain the geographic distribution of organ- organism fossil record, or its ecological tolerance. This has isms in terms of their evolutionary history. The latter usually revolutionized the discipline, allowing it to escape the dis- deals with longer time scales (millions of years), larger persal versus vicariance dilemma and to address a wider spatial scales (e.g., continental landmasses), and the distri- range of evolutionary questions, including the role of eco- bution patterns of species or higher taxa. This distinction, logical and historical factors in the construction of biomes or however, has become blurred in recent years. For example, the existence of contrasting patterns of range evolution in the young discipline of phylogeography (Avise 2000), often animals and plants. considered a part of historical biogeography, works with intermediate time scales of thousands of years and the Keywords Dispersal . Distribution patterns . Ecological distribution patterns of biological populations, such as those factors . Extinction . Historical processes . Vicariance formed after the retreat of the last glaciations at the end of the Quaternary. In addition, historical biogeography has begun lately to incorporate ecological information into I. Sanmartín (*) biogeographic reconstructions through techniques like Real Jardín Botánico, RJB-CSIC, ecological niche modeling (Lieberman 2000;Stigalland Plaza de Murillo 2, 28014 Madrid, Spain Lieberman 2005) and new analytical statistical methods e-mail: [email protected] (Ronquist and Sanmartín 2011). 556 Evo Edu Outreach (2012) 5:555–568 Vicariance vs. Dispersal: The Case of the Ratite Birds (e.g., the fossil record, information on past climates and geography, or the ecological tolerance of the group) to Biogeography is a very old discipline, dating back to the discriminate between them (Stigall and Lieberman 2006; time when the first naturalist explorers, such as Alexander Ronquist and Sanmartín 2011). In this review, I use the von Humboldt (1805), were intrigued by the fact that example of ratites to show how incorporating new sources regions with similar climates like the Mediterranean Basin of evidence into biogeographic reconstructions has allowed and Chile in South America exhibited faunas with similar researchers to address a wider range of evolutionary ques- physiognomies (life forms) but in which the inhabiting tions than the simple search for congruent distribution species were very different. Conversely, regions such as patterns. Africa and South America separated by large geographic barriers like the Atlantic Ocean show faunas of similar composition (Cox and Moore 2010). One of the best exam- Dispersalism and Centers of Origin ples of this type of disjunct geographic distribution is that of ratites, a primitive group of birds (Palaeognatha)that For centuries, dispersal was the dominant explanation sup- includes the ostriches, cassowaries, emus, rheas and kiwis. ported by a static concept of Earth and life. Darwin's theory This clade is distributed in all major southern continents of evolution (1859) changed this immutable view of species (Fig. 1a), but how did these flightless birds come to be by identifying the mechanism, natural selection, by which confined to a distribution scattered across different conti- organisms evolve into new species. But Darwin and his nents, now separated by thousands of miles of ocean? contemporaries, like Wallace (1876), still believed on the Two alternative biogeographic processes have been pro- idea of geological stability, according to which the position posed (Fig. 1b): dispersal—the ancestor of the group was and size of continents had not changed over time. New originally distributed in one of the areas, the “center of species evolved in a limited area, a “center of origin,” from origin,” from which it dispersed to the other areas by cross- which they dispersed to other regions over the same pattern ing a geographic barrier (e.g., the Southern Hemisphere of world geography that we see today (Cox and Moore ocean basins, Fig. 1b left); vicariance—the group ancestor 2010; Lomolino et al. 2006). This view was challenged by was distributed in a widespread area, then covering all its “extensionists” such as Joseph Dalton Hooker (1844), who present distribution, which became fragmented by succes- argued that long-distance dispersal across persistent barriers sive geographic barriers; this geographic division was fol- was unlikely, and instead continents must have been lowed by allopatric speciation, so that each member now connected in the past by tracts of dry land and now- survives in an isolated continent. The best example is the submerged landbridges over which organisms dispersed. breakup of the ancient supercontinent of Gondwana during Darwin and Wallace's idea of dispersal from a center of the Mesozoic-Cenozoic, which has often been argued to ex- origin continued to be dominant through the first half of plain austral disjunct distribution patterns such as that of the twentieth century, represented by the “New York school ratites (Fig. 1b right). In the dispersal explanation, the barrier of zoographers,” of which Matthew (1915), Darlington predates the geographic disjunction, whereas in the vicariant (1957), and Simpson (1953) were the most important pro- explanation, the appearance of the barrier causes the geo- ponents. The introduction of the theory of plate tectonics in graphic division, so it must be of the same age as the resulting geology, and especially the arrival of cladistics (see below), allopatric speciation event. led to a new approach, Phylogenetic Biogeography (Brundin Naturally, these processes are not mutually exclusive: for 1966;Hennig1966) that departed from the narrative dispersal example, the formation of the Panama isthmus between scenarios of the past. Although it was still based on the idea North and South America at the end of the Tertiary (3.5 of “dispersal” and “centers of origin,” it was also the first million years ago) was simultaneously a vicariant event—by approach to use information about the evolutionary relation- isolating marine organisms between the Atlantic and Pacific ships of organisms (in the form of a tree or cladogram) as the Oceans—and a dispersal event, since it established a new basis to infer their biogeographic history. For example, it migration route between North and South America for ter- assumed that in every speciation event, the species that restrial mammals, the “Great American Biotic Interchange” retained the ancestral (“plesiomorphic”) characteristics stayed (Simpson 1980). But for many decades, these two explan- closer to the original area, while the most derived (“apomor- ations were viewed as competing hypotheses in historical phic”) species was the one that dispersed (Crisci et al. 2003; biogeography, with proponents of one or another engaged in Cox and Moore 2010). Brundin (1966) was also pioneer in a polarized and sometimes heated debate (review in Cox and using geological information to interpret biogeographic histo- Moore 2010 and Lomolino et al. 2006). The current tenden- ries (Lomolino et al. 2006). cy is to accept both dispersal and vicariance explanations as Two criticisms have been raised against the dispersalist equally likely hypotheses and use other information sources approach to biogeography, especially by cladistic

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