opinion and perspectives ISSN 1948‐6596 perspective The causes and biogeographical significance of species’ rediscovery Richard J. Ladle 1,2,* , Paul Jepson 2 , Ana C. M. Malhado 1 , Steve Jennings 3 and Maan Barua 2 1. Institute of Biological and Health Sciences, Federal University of Alagoas, Maceio, AL, Brazil. 2. School of Geography and the Environment, University of Oxford, South Parks Road, Oxford, OX1 3QY, United Kingdom. 3. Oxfam GB, Oxfam House, John Smith Drive, Oxford, United Kingdom. *Author for correspondence: Dr Richard J. Ladle, Institute of Biological and Health Sciences, Federal Uni‐ versity of Alagoas, Praca Afrânio Jorge, s/n, Prado, Maceio, AL, Brazil, 57010‐020. e‐mail: richard.ladle@ouce.ox.ac.uk; http://www.geog.ox.ac.uk/staff/rladle.html Abstract. The rediscovery of a species that was putatively considered to be extinct can provide valuable data to test biogeographical hypotheses about population decline and range collapse. Moreover, such rediscoveries often generate much‐needed publicity and additional funds for the conservation of rare species and habitats. However, like extinction, rediscovery is challenging to define. In this perspective we argue that the ‘loss’ of a species and its subsequent rediscovery can be understood in terms of the interplay among four socio‐ecological factors: (1) the state of knowledge of species loss and rediscovery; (2) the presence of people and/or organizations with the interest, motivation, resources, skills and tech‐ nology to find target species; (3) the accessibility of the areas, habitats or sites where the species are thought to survive; and (4) the ease with which a species can be located when it is present within a habi‐ tat. Thus, species are ‘lost’ from scientific knowledge for different reasons and, consequently, not all rediscoveries are equally significant for biogeographical research or conservation. Indeed, rediscoveries of species that underwent a well documented decline and disappearance – and are therefore of greatest potential importance for both conservation and biogeographical research – appear to be poorly repre‐ sented in the literature compared to rediscovered species that were only known from a handful of mu‐ seum specimens. Thus, carefully distinguishing between the causes of temporal gaps in zoological re‐ cords is essential for improving the utility of rediscovery data for biogeographical research and conser‐ vation practice. Keywords: extinction, range collapse, rarity, critically endangered, monitoring Introduction Rediscoveries of putatively extinct species are of great potential interest to both conservationists and biogeographers (Crowley 2011). For the for‐ mer, ‘rediscovery’ can be a considerable conserva‐ tion policy and publicity asset (Ladle and Jepson 2008, Ladle et al. 2009) – as testified by recent global initiatives: in 2009 BirdLife International launched a “global bid to try to confirm the con‐ tinued existence of 47 species of bird that have not been seen for up to 184 years” (BirdLife Inter‐ national 2009). The following year Conservation International launched its “Search for lost Frogs” which involves a dedicated campaign and expedi‐ tions to 18 countries seeking to locate 40 species not seen for a decade or more (Conservation In‐ ternational 2010) – at the time of writing 12 spe‐ cies have been rediscovered. Moreover, since re‐ discovered species are typically exceedingly rare and geographically localized, new knowledge on population status and distribution supports effec‐ tive conservation interventions. Finally, rediscov‐ eries remove uncertainty from extinction risk as‐ sessments; a confirmed new record moves the species from ‘extinct’ or ‘probably extinct’ and into an IUCN threat (or data deficient) category. For biogeographers, species rediscovery has both a practical and conceptual significance. From the frontiers of biogeography 3.3, 2011 — © 2011 the authors; journal compilation © 2011 The International Biogeography Society