on the use of taxon:2 columnas 15/11/2010 13:53 Página 111 Islands and Evolution (2010). Pérez-Mellado, V. and Ramon, C. (eds.) Institut Menorquí d’Estudis. Recerca, 19: 111-146 ON THE USE OF TAXON SUBSTITUTES IN REWILDING PROJECTS ON ISLANDS DENNIS M. HANSEN Abstract. Recent proposals to rewild and highlight promising avenues for continental ecosystems with taxon future research and restoration mana- substitutes –replacing extinct species with gement. extant analogues– have met with Key words: na turalness, extinction, controversy, chiefly because the involved restoration, ecological analogues, plant- species are extinct Pleistocene mega- animal interactions, ecosystem functio- fauna and their still-extant counterparts, ning, assisted migration. and because of the massive areas required. In contrast, I argue that island Resumen. La s recientes propuestas rewilding offers ideal and much less para repoblar ecosistemas continentales controversial scenarios to rapidly con taxones sustitutivos (reemplazando advance our empirical understanding of las especies extinguidas con otras vi- taxon substitutions. The main reasons vientes análogas) han sido objeto de are twofold: firstly, anthropogenic controversia, especialmente porque las extinctions happened very recently on especies involucradas formaban parte islands, often within the last few de la megafauna extinguida del Pleisto- centuries; secondly, island species are ceno, al igual que sus todavía vivientes much smaller and require less space to contrapartes y también porque se preci- implement rewilding projects. Island san áreas de una gran extensión. Por el rewilding offers hope for restoring even contrario, propongo que la repoblación highly degraded island ecosystems de las islas ofrece escenarios ideales y where many species have been lost, and mucho menos controvertidos, para allows radically different restoration avanzar rápidamente en nuestra com- trajectories to be pursued than those prensión empírica de la sustitución de ta- available with the surviving native xones. Las razones principales son species pools. I here present an overview dobles: en primer lugar, las extinciones of currently ongoing, planned, and antropogénicas han sucedido en las is- proposed taxon substitution projects on las muy recientemente, frecuentemente islands, discuss several salient points, en los últimos siglos; en segundo lugar, Department of Biology, 371 Serra Mall, Stanford University, Stanford, CA94305-5020, USA. [email protected] 111 on the use of taxon:2 columnas 15/11/2010 13:53 Página 112 HANSEN las especies insulares son mucho más contrapartes i també perquè es precisen pequeñas y requieren menos espacio àrees d'una gran extensió. Per contra, para implementar los proyectos de re- proposo que la repoblació de les illes población. La repoblación insular ofrece ofereix escenaris ideals i molt menys una esperanza para restaurar incluso controvertits, per avançar ràpidament ecosistemas insulares intensamente de- en la nostra comprensió empírica de la gradados, donde muchas especies se substitució de taxons. Les raons han perdido y permite seguir trayectorias principals són dobles: en primer lloc, les de restauración radicalmente diferentes extincions antropogèniques han succeït de aquéllas disponibles con el conjunto a les illes molt recentment, freqüentment de especies nativas supervivientes. Pre- als últims segles; en segon lloc, les sento aquí el panorama de los proyec- espècies insulars són molt més petites i tos de sustitución en islas que se hallan requereixen menys espai per imple- en curso de realización, en planifica- mentar els projectes de repoblació. La ción o propuestos, discuto numerosos repoblació insular ofereix una espe- puntos a resaltar y señalo las promete- rança per restaurar fins i tot ecosistemes doras líneas de futura investigación y insulars intensament degradats, on de manejo de la restauración. moltes espècies s'han perdut i permet seguir trajectòries de restauració radi- Palabras clave. Na turalidad, extin- calment diferents d'aquelles disponibles ción, restauración, análogos ecológicos, amb el conjunt d'espècies natives interacciones planta-animal, funciona- supervivents. Presento aquí el panorama miento de los ecosistemas, migración dels projectes de substitució en illes que asistida. es troben en curs de realització, en Resum. Les recents propostes per planificació o proposats, discuteixo repoblar ecosistemes continentals amb nombrosos punts a ressaltar i assenyalo taxons substitutius (reemplaçant les les prometedores línies de futura espècies extingides amb altres vivents investigació i de maneig de la anàlogues) han estat objecte de restauració. controvèrsia, especialment perquè les Paraules clau. Na turalitat, extinció, espècies involucrades formaven part de restauració, anàlegs ecològics, inter- la megafauna extingida del Plistocè, accions planta-animal, funcionament igual que els seus encara vivents dels ecosistemes, migració assistida. 112 on the use of taxon:2 columnas 15/11/2010 13:53 Página 113 ISLAND REWILDING INTRODUCTION “...stars, comets and extinct species share another convenient property that appeals to people. Not only are they very interesting, but there is nothing we can actually do about them either. By this I mean that we are powerless to intervene to change what happens to them or what they do (or did). So discovering more about them carries no responsibility; they are the ultimate, free, intellectual curiosity trip, devoid of any need to 'do' anything when we discover more about them” Lawton, 1995 “The ecology of the afterlife is alive and well” Lawton, 1995 Many studies have documented by many of these ‘ghost species’–yet how the majority of island ecosystems there is no doubt that on many islands are badly damaged after catastrophic they fulfilled important functional roles anthropogenic impacts that mainly until very recently, for example as occurred within the last two millennia, herbivores, frugivores and pollinators depending on the date of human (e.g. Cox and Elmqvist, 2000; colonisation. However, adding to the McConkey and Drake, 2002; Godfrey already overwhelming litany of et al., 2008; Hansen and Galetti, 2009). ecosystem destruction on islands is not As essential as modern-day conser- the topic of the present contribution. As vation of endangered species and Donlan et al. (2005) succinctly put it, habitats is in halting the sixth mass more than enough has sadly been extinction, some ecologists and written about the “doom and gloom” practitioners have come to realise that facing Earth’s biodiversity. we ignore the ecological and evolutionary consequences of these Between the two opening quotes by functional gaps at our own peril. John Lawton, one could say, lies the emerging field of rewilding with taxon For continental ecosystems, these substitutes, resurrecting the lost views have resulted in several recent ecosystem functions of recently extinct suggestions to rewild large tracts of species by substituting them with extant continental ecosystems, in North species (unless stated otherwise, America, South America and Eurasia ‘rewilding’ hereafter refers to restoration (Galetti, 2004; Donlan et al., 2005; practices involving taxon substitutes). Zimov, 2005; Donlan et al., 2006), all Even though extinctions on islands of which aim to replace extinct happened so recently, and are being Pleistocene megafauna and restore lost increasingly well documented through ecosystem dynamics. The notion that it the discovery of subfossil material, there may be possible to get one up on that is still a widespread disregard of the most ultimate of anthropogenic ecological and evolutionary roles played disturbance regimes, extinction, may 113 on the use of taxon:2 columnas 15/11/2010 13:53 Página 114 HANSEN seem heretic to some, and certainly has more complex mainland settings. sparked controversy (Rubenstein et al., However, taking this metaphor at face 2006; Caro, 2007; Caro and Sherman, value, Holocene extinction events on 2009; Donlan and Greene, 2010). islands worldwide have left the laboratories more than half empty and In contrast to this, I believe islands sorely in need of equipment―from a offer some of the best suited scenarios plethora of pipet-tips and test tubes to to rapidly advance our empirical lumbering gas-chromatographs. Pro- understanding of rewilding and perly applied, rewilding is an explicit, exploring the use of taxon substitutions hypothesis-driven and adaptive mana- in conservation and restoration (see also gement option that adds a promising Griffiths and Harris, 2010; Griffiths et tool to the growing arsenal available to al., 2010; Hansen et al., 2010; Kaiser- island restoration projects―re-stocking Bunbury et al., 2010). This is chiefly the laboratories, so to speak. because the relevant temporal and spatial scales are much smaller on Island rewilding is inherently part of islands. Temporally, the majority of a whole-ecosystem view of restoration island species went extinct very recently, (Steadman and Martin, 2003; Lazell, often within the last five centuries. This 2005; Hutton et al., 2007; Jones, contrasts greatly with the peak of 2008), and is closely allied to the continental megafauna extinctions concept of ‘inter-situ’ conservation thousands of years ago, in the championed by Burney and Burney Pleistocene, and puts most island ghosts (2007), which they define as: “The squarely in the youngest category of establishment of species by reintro- Lawton’s (1995) poetically termed duction to locations