Climate change, sea-level rise, and conservation:keeping island biodiversity afloat

Franck Courchamp1, Benjamin D. Hoffmann2, James C. Russell3, Camille Leclerc1, andCeline Bellard1

1 Ecologie, Syste matique et Evolution, UMR CNRS 8079, University of Paris Sud, Orsay Cedex 91405, France2 CSIRO, Ecosystem Sciences, PMB 44, Winnellie, NT 0822, Australia3 University of Auckland, School of Biological Sciences and Department of Statistics, Private Bag 92019, Auckland 1142,

New Zealand

Forum

Island conservation programs have been spectacularlysuccessful over the past five decades, yet they generallydo not account for impacts of climate change. Here, weargue that the full spectrum of climate change, especiallysea-level rise and loss of suitable climatic conditions,should be rapidly integrated into island biodiversityresearch and management.

Island conservation in the longer termConservation of biodiversity on islands is important globallybecause islands are home to more than 20% of the terrestrialplant and vertebrate species in the world, within less than5% of the global terrestrial area. Endemism on islands is amagnitude higher than on continents [1]; ten of the 35biodiversity hotspots in the world are entirely, or largelyconsist of, islands [2]. Yet this diversity is threatened: overhalf of all recent extinctions have occurred on islands, whichcurrently harbor over one-third of all terrestrial speciesfacing imminent extinction [3] (Figure 1).

In response to the biodiversity crisis, island conserva-tion has been an active field of research and action. Hun-dreds of invasive species eradications and endangeredspecies translocations have been successfully completed[4–6]. However, despite climate change being an increasingresearch focus generally, its impacts on island biodiversityare only just beginning to be investigated. For example,invasive species eradications on islands have been prior-itized largely by threats to native biodiversity, eradicationfeasibility, economic cost, and reinvasion potential, buthave never considered the threat of sea-level rise. Yet,the probability and extent of island submersion wouldprovide a relevant metric for the longevity of long-termbenefits of such eradications.

The impact of sea-level rise on islandsRecent research suggests that impacts on islands from sea-level rise will be substantial [2,7–9]. Current scenarios for

0169-5347/$ – see front matter

� 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.tree.2014.01.001

Corresponding author: Courchamp, F. (franck.courchamp@u-psud.fr).Keywords: sea-level rise; climate change; climatic niche shift; island conservation;prioritization.

sea-level rise vary from 0.26 to 2.3 m by 2100, whereas arise of 2 or 3 m might happen in the following centuries (see[2,10] and references therein). Moreover, greater tidalranges, in particular centennial tides, will lead to periodicfloods that will destroy nonsaline habitats. Increased fre-quency and amplitude of seawater floods are also expectedto be more common with global climate change. Sea-levelrise will also increase coastal erosion (e.g., in the range of50–200 times that of sea-level rise) and saline water intru-sion [9]. Furthermore, shoreline retreat will also lead tomassive displacement of anthropogenic activities fromcoasts [9], which will lead to additional habitat loss furtherinland.

Despite clear and imminent risks, the consequences ofsea-level rise for island biodiversity remain one of the leaststudied of all climate-change issues, both locally andglobally, which is surprising when one considers boththe number of islands concerned (over 180 000 worldwide)and the potential impact. Even with the most optimisticscenario, many low-lying islands will simply be entirelysubmerged, threatening most of their biodiversity andmany benefits from recent conservation actions. A recentanalysis focusing on 4500 islands in ten biodiversity hot-spots suggested that 6–19% of these islands could beentirely submerged with a 1–6 m sea-level rise, threaten-ing over 300 endemic species with extinction [2]. Giventhat they represent the largest proportion of the existingislands, most (69%) of the threatened islands are conti-nental. Yet, unsurprisingly, coral atolls, which arebelieved to comprise almost 15% of all islands, are dis-proportionately threatened (27%). A similar study in thePacific and South East Asia predicted that 15–62% of12 900 islands could be completely inundated [8]. Moreglobally, a recent study of over 1200 islands from all oceansfound comparable results, suggesting a possibility of6–12% of islands worldwide being entirely submerged[7]. This would amount to a total loss of 10 000–20 000of the 180 000 islands worldwide, with many more suffer-ing partial losses.

The change of climates on islandsClimatic shift is another issue that is particularly perti-nent to island conservation. Following climate change, thearea of climatic parameters that is suitable for any givenspecies is expected to change spatially, within this century[11]. These shifts will occur predominantly upward

Trends in Ecology & Evolution, March 2014, Vol. 29, No. 3 127

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Already ex�nct

Facing imminent ex�nc�on

49

24

121

8

27

16

51

80

89

128

328

95

TRENDS in Ecology & Evolution

Figure 1. Proportion of extinct and threatened species on islands (dark gray) and

the mainland (light gray). Numbers are species and represent mammals ( ),

birds ( ), and reptiles and amphibians ( ), showing that terrestrial vertebrate

biodiversity is generally more threatened on islands. Data from [3].

Forum Trends in Ecology & Evolution March 2014, Vol. 29, No. 3

(in altitude) and poleward (in latitude). On small islands,this shift may project suitable climates hundreds of kilo-meters beyond island limits. Consequently, small islandsare likely to have a complete change of climatic parametersover their entire surface and many species on those islandswill potentially face unsuitable climatic conditions.Whereas continental species can avoid extinction bymigrating to follow the climate shift, many insular speciescannot. Thus, because such species will be unable to dis-perse from their original island, they would have to adaptrapidly or will become extinct.

Where not already done so, climate change shouldimmediately be integrated into research and managementprograms for island biodiversity. Here, we highlight twoapproaches for doing just that, which will identify solutionsthat will help safeguard biodiversity and protect conserva-tion investments against future global climate change.

Account for sea-level rise when prioritizing islandrestorationOver 900 successful eradications of alien invasive verte-brates have been conducted on islands worldwide (http://eradicationsdb.fos.auckland.ac.nz). In most cases, such as

128

the Surprise Island project, restoration was conductedwithout a consideration of climate change (Box 1), result-ing in some suboptimal choices for long-term conservationbenefits. In January 2010, rat eradication led by one of us(J.C.R.) on the 28-ha island of Honuea (in Tetiaroa, an atollin the Windward group of the Society Islands of FrenchPolynesia) failed because it was completely flooded bytropical cyclone Oli the day after final baiting occurredthroughout the island. Increased frequency and amplitudeof cyclones following climate change are indeed increas-ingly likely to flood low-lying islands and interfere withconservation programs.

Of 604 islands where invasive vertebrates have beeneradicated and for which elevation data are available[2,12], 26 are predicted to be completely inundated witha 1 m increase in sea level, and many more will be impactedby partial habitat loss (Figure 2). Researchers are increas-ingly developing prioritization frameworks to help guidedecision-making on which islands should be targeted forrestoration via invasive species removal. Quite simply, theanticipated level of island submersion should become oneof the primary factors to consider for restoration prioritiza-tion, so that conservation gain is further optimized, andover longer time horizons. To do so, geographic data, suchas island area and elevation profile, and a variety ofinundation models at local, regional, and global scales[13], will need to be explicitly incorporated into prioritiza-tion frameworks. Consequently, islands with greater ele-vations may become a priority for invasive specieseradication, which will require further research to increasethe scale of island eradications, because islands withgreater elevations are also often larger. Such islands willalso suffer complex exposure to climate change.

Consider translocations to save island species fromclimate changeFor many island species that cannot adapt or migrate to asuitable nearby island, practitioners will eventually befaced with a decision to either let them go extinct by doingnothing or to attempt to save them by actively movingthem to suitable habitat. Species translocations have longbeen a powerful conservation tool, especially for islandconservation, but are controversial, because they can alsolead to biological invasions. Many translocations wereoriginally to islands, to alleviate impacts of alien invasivespecies [6]; however, in the future, translocations may haveto be from islands to mitigate climate loss [5]. Thus, theassisted migration of threatened species from islands willrequire a framework that considers not only the probabilityof success and lack of impacts in the new introduced range[14], but also the more intractable value issues that emergewhen deciding how to manage species [15], such as whichspecies to move, when, and to where.

Concluding remarks: securing long-term conservationbenefitsCurrently, the removal of invasive species from islands isone of the most powerful tools for preventing extinctionsand restoring ecosystems. To safeguard the biodiversitybenefits secured through these restoration programs andto maximize future benefits, implications of climate change

Box 1. The restoration of Surprise Island

In the coming decades, thousands of low-lying coral atolls around the

world will be vulnerable to sea-level rise, predominantly due to

expansion of ocean water and mass loss of mountains glaciers and ice

sheets. Tropical atolls of some island nations are already experiencing

inundation. Importantly, sea-level rise is predicted to be heteroge-

neous: due to spatial heterogeneity of surface temperatures and other

complex, interacting sets of factors, sea levels in some oceanic areas

will rise more than in others. Thus, the persistence of atoll islands will

depend strongly on location, local conditions, and geomorphology.

Therefore, on some of these islands, the conservation benefits of

important restoration efforts may be lost in the long term.

Surprise Island (Figure I), located in the Entrecasteaux reef off New

Caledonia, provides one example of island conservation research and

action that did not integrate climate change. Only a few meters above

sea level, the small and remote island was the focus of a research

program that ended in 2009 with the eradication of introduced rats

(Rattus rattus), mice (Mus musculus), and an invasive plant (Cassytha

filiformis). The eradication of alien invasive species from Surprise

Island was a positive conservation action. It has undoubtedly helped

protect the local species for the coming decades, possibly preventing

some of them from local extinction. In addition, it provided a wealth of

knowledge necessary for island conservation that can be applied to

other islands. Notably, research investigating species interactions

helped mitigate unexpected ecological chain reactions during eradica-

tions, which has been observed during other eradication programs.

Research and conservation actions were a result of substantial

investment in resources, lasting over a decade. Despite careful

planning and long-term commitment, it did not occur to those of us

involved in this program (F.C.) that expected sea-level rise would

threaten the benefits from our conservation actions.

Many other alien species eradication programs have taken place on

islands that are doomed in the long term by sea-level rise. Of course,

most of these eradication efforts occurred before current under-

standing of climate change and an ability to measure its impacts. Also,

on some of these islands, a rapid conservation response was required

despite the long-term threat of climate change. Nonetheless, future

conservation programs must take the full breadth of climate change

into account, by prioritizing islands according to threats from sea-level

rise and climate shifts, and by considering translocation of island

species that will be lost to climate change.

TRENDS in Ecology & Evolution

Figure I. Surprise Island (24 ha), 230 km north of New Caledonia.

Forum Trends in Ecology & Evolution March 2014, Vol. 29, No. 3

must become a priority for research and conservationagendas. Research should focus on better understandingand predicting the impacts of sea-level rise and climaticshifts at both the organismal and ecosystem levels onislands. Researchers and practitioners should rapidly

Figure 2. Predicted area submersion on islands with an invasive vertebrate eradicat

immersion. With a 1-m sea-level rise, 4% (26) of the 604 islands with an eradication prog

habitat. Islands and their elevations come from the Database of Island Invasive Species

integrate these effects of climate change into the planningand prioritizations that are currently taking place. Theyalso should begin to assess island species that are mostlikely to be at risk from future climate change and theoptions for preventing their extinction.

0%Key:

0–20%20–40%40–60%60–80%80–100%100%

TRENDS in Ecology & Evolution

ion program. The size and color of points represent the percentage of surface

ram would be entirely under water and many more would lose a large part of their

Eradications [4], which is combined with the island sea-level rise model from [2].

129

Forum Trends in Ecology & Evolution March 2014, Vol. 29, No. 3

AcknowledgmentsWe thank Nick Holmes for access to the Island Invasive SpeciesEradications Database and C. Josh Donlan for discussions and input onthe draft manuscript. Two anonymous referees provided helpful feedbackon the manuscript. F.C., C.L., and C.B. were supported by the AgenceNationale de la Recherche. B.D.H. and J.C.R. thank the Ecologie,Systematique et Evolution laboratory at the University of Paris Sud forhospitality. J.C.R. was supported by a sabbatical grant-in-aid from theUniversity of Auckland.

References1 Kier, G. et al. (2009) A global assessment of endemism and species

richness across island and mainland regions. Proc. Natl. Acad. Sci.U.S.A. 23, 9322–9327

2 Bellard, C. et al. (2013) Impact of sea level rise on the 10 insularbiodiversity hotspots. Global Ecol. Biogeogr. 23, 203–212

3 Ricketts, T.H. et al. (2005) Pinpointing and preventing imminentextinctions. Proc. Natl. Acad. Sci. U.S.A. 102, 18497–18501

4 Veitch, C.R. et al. (2011) Island Invasives: Eradication andManagement, IUCN

5 Thomas, C.D. (2011) Translocation of species, climate change, and theend of trying to recreate past ecological communities. Trends Ecol.Evol. 26, 216–221

130

6 Armstrong, D.P. and Seddon, P.J. (2008) Directions in reintroductionbiology. Trends Ecol. Evol. 23, 20–25

7 Bellard, C. et al. (2013) Impact of sea level rise on the french islandsworldwide. Nat. Conserv. 5, 75–86

8 Wetzel, F.T. et al. (2013) Vulnerability of terrestrial islandvertebrates to projected sea-level rise. Global Change Biol. 19,2058–2070

9 Wetzel, F.T. et al. (2012) Future climate change driven sea-level rise:secondary consequences from human displacement for islandbiodiversity. Global Change Biol. 18, 2707–2719

10 Levermann, A. et al. (2013) The multimillennial sea-level commitmentof global warming. Proc. Natl. Acad. Sci. U.S.A. 110, 13745–13750

11 Mora, C. et al. (2013) The projected timing of climate departure fromrecent variability. Nature 502, 183–187

12 Bellard, C. et al. (2012) Impacts of climate change on the future ofbiodiversity. Ecol. Lett. 15, 365–377

13 Mcleod, E. et al. (2010) Sea-level rise impact models and environmentalconservation: a review of models and their applications. Ocean Coast.Manag. 53, 507–517

14 Rout, T.M. et al. (2013) How to decide whether to move speciesthreatened by climate change. PLoS ONE 8, e75814

15 Redpath, S.M. et al. (2012) Understanding and managing conservationconflicts. Trends Ecol. Evol. 28, 100–109

Conservation of low-islands: high priority despitesea-level rise. A comment on Courchamp et al.

Serge Andrefoue t1, Jerome Aucan2, Herve Jourdan3, Paul Kench4,Christophe Menkes5, Eric Vidal3, and Hiroya Yamano6

1 Institut de Recherche pour le De veloppement (IRD), Unite de Recherche 227 CoRe Us, LABEX CORAIL, BP A5, 98848 Noume a,

New Caledonia2 Institut de Recherche pour le De veloppement, Laboratoire d’Etudes en Ge ophysique et Oce anographie Spatiale (LEGOS), BP A5,

98848 Noume a, New Caledonia3 Institut Me diterrane en de Biodiversite et d’Ecologie Marine et Continentale (IMBE), Aix-Marseille Universite ,

Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le De veloppement (IRD),

Universite d’Avignon et des Pays de Vaucluse (UAPV), Centre IRD Noume a, BP A5, 98848 Noume a, New Caledonia4 School of Environment, The University of Auckland, New Zealand5 Institut de Recherche pour le De veloppement, Sorbonne Universite s (Universite Pierre et Marie Curie; Universite Paris 06)–

CNRS–Muse um National d’Histoire Naturelle–Institut Pierre Simon Laplace, LOCEAN Laboratory, IRD Noume a, BP A5, 98848

Noume a, New Caledonia6 National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan

No triage conservation strategy for low tropical islands!Assuming that a simple drowning model is applicable to allislands facing future climate change and sea-level rise(SLR), the future existence of up to 12% of islands is saidto be compromised – and therefore these should not beconsidered for active management and protection[1,2]. This includes tropical atolls and their low-lyingislands. However, we reject the triage strategy elaboratedby Courchamp et al. [1]. Evidence from geology, sedimen-tology, and oceanography, and from the ecology of invasivespecies, shows that island conservation, especially of lowislands, should remain a priority.

Geological, sedimentary, relative SLR, and tectonicevidenceSimplistic drowning models over-state the risks and areinappropriate for low-lying coral reef islands. Such model-ing assumes that islands are passive geological entitiesthat will experience permanent inundation with SLR andare unable to physically respond. This is only likely forhard rock coasts, whereas sedimentary shorelines, includ-ing coral reef islands which are composed of sand andgravel, display a diverse range of physical responses.

During the mid-Holocene (6000–2000 years ago), mor-phostratigraphy and radiometric dating show that reefislands formed under rising, falling, and stable sea levels.Islands in the Maldives and Marshall Islands formedunder rising sea levels (�0.5–1.0 m higher than present)[3,4], whereas some Great Barrier Reef and New Caledo-nian reef islands formed at stable higher sea levels [5]. Inthese regions sea levels subsequently fell to current levels2000 years ago. Over the next century the sea level willsimply reoccupy the levels under which the islands formed.

At decadal timescales, instead of simply eroding orshrinking, islands can display a complicated spectrum ofgeomorphic responses. Over the past half-century, under aSLR of �2.0 mm/year, reef islands in the Tuvalu andMarshall Islands have remained stable in size or havebecome larger [6]. Islands are dynamic landforms thatcan adjust their shape and position on reefs and buildvertically. Physical island change is mediated by the sup-ply and transport of coral sediment rather than by sea level[4]. As waves and currents change, island sediments arereworked alongshore, around shorelines, or onto islandsurfaces via overwash processes allowing island surfacesto aggrade. In the Maldives, large sections of islands havevertically accreted by 0.3 m over the past decade, a ratemuch larger than anticipated sea-level rise.

At centennial timescales, the 5th IPCC (Intergovern-mental Panel on Climate Change) reports that the rate ofglobal mean SLR during the 21st century will exceed the1971–2010 rate for all representative concentration path-way (RCP) scenarios [7]. However, SLR will also exhibitstrong regional variations from the mean trend. Thus,a simple drowning model with a globally uniform sealevel would be inappropriate for taking conservationdecisions.

Major uncertainty in centennial projections lies in decad-al variations, which can differ by more than 100% from theglobal long-term projected change [7]. For instance, duringthe past 20 years the Solomon Islands and Micronesia haveexperienced SLR rates above 10 mm.y�1. Conversely, NewCaledonia has experienced rates lower than 1 mm.y�1 overthe past 50 years, and conclusions about future impacts arevery uncertain. Stating that conservation efforts in SurpriseIsland (New Caledonia) are doomed therefore seems to beinappropriate [1].

Tectonic processes can also cause vertical land move-ments that have a predominant role compared to SLR[8]. For instance, in the Torres Islands (Vanuatu) thedrowning rate can be much higher than that caused by

Letters

0169-5347/

� 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.tree.2014.10.001

Corresponding author: Andrefouet, S. (serge.andrefouet@ird.fr)

Trends in Ecology & Evolution, January 2015, Vol. 30, No. 1 1

SLR. Conversely, uplift (e.g., following earthquakes, asoccurred recently in the Futuna, Vanuatu, and SolomonIslands) can offset SLR.

Conservation strategy and invasive speciesLow-lying islands, including coral atolls, contain irreplace-able features without any equivalent on high islands.For instance, many seabirds nest on low islands wherethey are impacted by introduced animals [9], with one-third of seabird species now being considered to be at risk ofextinction. In many cases, control or eradication of aliens inthese islands promoted rapid recolonization by seabirds.Abandoning such initiatives would impact negatively uponthese populations.

Invasive species are one of the primary extinctiondrivers on islands. Certainly, eradication programs onislands expected to drown shortly would be a waste ofeffort. However, we contend that the number of entirelydrowned islands has been grossly overestimated. Partiallyflooded islands will need better management because theimpact of exotic species is likely to become stronger withshrinking, fragmented habitats [10].

Finally, species translocation was proposed to mitigateSLR effects [1]. Translocation can represent a last-chancestrategy, but this should not be seen as an innocuous tool.It can produce unpredictable ecosystem changes on receiv-ing islands [11]. Instead, low-lying islands should be pri-oritized in restoration programs through invasive specieseradication, especially when critically endangered andendemic populations are still remnant.

To conclude, low-lying islands are at the forefront of theconsequences of global change but responses to SLR will behighly variable. A simple and globally uniform approach

to drowning will yield errant results, and is an inappropri-ate basis upon which to prioritize conservation efforts.Conservationists cannot be passive about low-lyingislands. They represent irreplaceable sentinels to observethe interplays between climate change and biological inva-sions, and to experiment the best strategies and means tomitigate their effects.

References1 Courchamp, F. et al. (2014) Climate change, sea-level rise, and

conservation: keeping island biodiversity afloat. Trends Ecol. Evol.29, 127–130

2 Bellard, C. et al. (2014) Impact of sea level rise on the 10 insularbiodiversity hotspots. Global Ecol. Biogeogr. 23, 203–212

3 Kench, P.S. et al. (2005) New model of reef-island evolution: Maldives,Indian Ocean. Geology 33, 145–148

4 Kench, P.S. et al. (2014) Evidence for coral island formation during risingsea level in the Central Pacific Ocean. Geophys. Res. Lett. 41, 820–827

5 Yamano, H. et al. (2014) Late Holocene sea-level change and reef-islandevolution in New Caledonia. Geomorphology 222, 39–45

6 Ford, M.R. and Kench, P.S. (2014) Formation and adjustment oftyphoon-impacted reef islands interpreted from remote imagery:Nadikdik Atoll, Marshall Islands. Geomorphology 214, 216–222

7 Church, J.A. et al. (2013) Sea level change. In Climate Change 2013:The Physical Science Basis. Contribution of Working Group I to theFifth Assessment Report of the Intergovernmental Panel on ClimateChange (Stocker, T.F. et al., eds), pp. 1137–1216, Cambridge UniversityPress

8 Ballu, V. et al. (2011) Comparing the role of absolute sea-level rise andvertical tectonic motions in coastal flooding, Torres Islands (Vanuatu).Proc. Natl. Acad. Sci. U.S.A. 108, 13019–13022

9 Spatz, D.R. et al. (2014) The biogeography of globally threatenedseabirds and island conservation opportunities. Conserv. Biol. 28,1282–1290

10 Blackburn, T.M. et al. (2004) Avian extinction and mammalianintroductions on Oceanic islands. Science 305, 1955–1958

11 Ricciardi, A. and Simberloff, D. (2009) Assisted colonization is not aviable conservation strategy. Trends Ecol. Evol. 24, 248–253

Adapting island conservation to climate change.Response to Andrefoue t et al.

Celine Bellard1, James Russell2, Benjamin D. Hoffmann3, Camille Leclerc1, andFranck Courchamp1,4

1 Ecologie, Syste matique, and Evolution, Centre National de la Recherche Scientifique (CNRS) Unite Mixte de Recherche 8079,

University of Paris Sud, Orsay CEDEX 91405, France2 University of Auckland, School of Biological Sciences and Department of Statistics, Private Bag 92019, Auckland 1142,

New Zealand3 Commonwealth Scientific and Industrial Research Organisation (CSIRO), Ecosystem Sciences, PMB 44, Winnellie,

Northern Territory 0822, Australia4 Department of Ecology and Evolutionary Biology and Center for Tropical Research, Institute of the Environment and

Sustainability, University of California Los Angeles, CA 90095, USA

In a recent Forum article [1] we argued that conservationon islands should better incorporate climate change in

management prioritization schemes. Most species atrisk of extinction are threatened by multiple factors [2]including habitat loss, biological invasions, pollution,overexploitation, and climate change. In particular, biolog-ical invasions are currently the greatest cause of insularbiodiversity decline [3], but climate change and sea-levelrise are likely to become more significant threats in the

0169-5347/

� 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.tree.2014.11.003

Corresponding author: Bellard, C. (celine.bellard@u-psud.fr)

Letters Trends in Ecology & Evolution January 2015, Vol. 30, No. 1

2

future [4]. We argued that most conservation programs orprioritization schemes are still implemented focusing onone threat only (e.g., [5]), but several threats will almostalways occur simultaneously, and sometimes synergisti-cally [6]. We also proposed that island conservation priori-tization exercises must include geographic data, such asisland area and elevation profile, and a variety of sea-levelrise inundation models at local, regional, and global scales.Our goal was to help effect better prioritization of manage-ment actions and durably maximize conservation out-comes. In response, Andrefouet et al. [7] supported ourcall for better prioritization of island conservation, withparticular emphasis on the eradication of invasive speciesfrom low-lying islands.

Andrefouet et al. [7], however, understood our call as onefor a ‘triage conservation strategy’, meaning that we sug-gest abandoning low tropical islands. Importantly, we byno means suggest this, but make the point that continuing‘business as usual’ is not an option if limited conservationresources are to be efficiently allocated to effectively pre-vent biodiversity loss. Investing resources on invasivealien species removal programs makes most sense onislands where biodiversity will persist, unless eradicationis an interim step before translocation. If not, such effortswill be annulled, resulting in both a loss of investment andcredibility in the eyes of funders and the public. Such lossesare even less acceptable when the outcome was predictableand alternative islands were available where pest removalwould have had a longer-lasting effect.

The claim by Andrefouet et al. [7] that ‘low-lying islandsshould be prioritized in restoration programs throughinvasive species eradication’ perpetuates the risk of focus-ing on prioritization by single threats, and optimizes bio-diversity only in the short term. Such overly simplisticmanagement needs to be reconsidered, especially whensophisticated algorithms are now available for conserva-tion prioritization incorporating multiple threats, values,and uncertainties [8]. Adapted prioritization schemes canaccount for the uncertainty associated with estimates ofclimate change, sea-level rise, or even physical responsesof islands, if any. Terrestrial continental conservationprograms are already well advanced in incorporating mul-tiple threats to biodiversity management (e.g., [9,10]) andit behoves island conservation to follow suit. Conservationefforts would not prioritize invasive species managementin a continental area that was about to be clear-felled; whywould it be more sensible to conduct an eradication on a

low island if there is a high risk that the island will bepermanently inundated in the near future? In addition, weproposed translocation to protect species in response toclimate change. Rather than a ‘last-chance strategy’, assuggested by Andrefouet et al. [7], we see translocation as apowerful, and under-utilized, conservation tool to returnspecies throughout their former range, including on bothhigh and low islands, such as has been implemented sosuccessfully in New Zealand [11]. This is certainly a topicon which research and discussion should and will continue;regardless, as often in conservation biology, the need fordifficult management decisions will remain.

Ultimately, island conservationists need to strike abalance as to whether it is strategically better to prioritizeconservation efforts based only on current threats, or alsoto account for future threats such as climate change. Wesuggest that the latter maximizes the time-horizon forisland conservation, and we reiterate our call for relevantprioritizations incorporating multiple current and futurethreats and all levels of uncertainty, as has been done inother systems (e.g., [9]), to better prioritize, protect, andrestore island ecosystems.

References1 Courchamp, F. et al. (2014) Climate change, sea-level rise, and

conservation: keeping island biodiversity afloat. Trends Ecol. Evol.29, 127–130

2 Tingley, M.W. et al. (2013) Climate change must not blow conservationoff course. Nature 500, 271–272

3 Simberloff, D. et al. (2013) Impacts of biological invasions: what’s whatand the way forward. Trends Ecol. Evol. 28, 58–66

4 Bellard, C. et al. (2012) Impacts of climate change on the future ofbiodiversity. Ecol. Lett. 15, 365–377

5 Dawson, J. et al. (2014) Prioritizing islands for the eradication ofinvasive vertebrates in the United Kingdom Overseas Territories.Conserv. Biol. 00, 1–11

6 Sala, O.E. et al. (2000) Global biodiversity scenarios for the year 2100.Science 287, 1770–1774

7 Andrefouet, S. et al. (2015) Conservation of low-islands: high prioritydespite sea-level rise. A comment on Courchamp et al. Trends Ecol.Evol. 30, 1–2

8 Bottrill, M.C. et al. (2008) Is conservation triage just smart decisionmaking? Trends Ecol. Evol. 23, 649–654

9 Evans, M.C. et al. (2011) What to do in the face of multiple threats?Incorporating dependencies within a return on investment frameworkfor conservation. Divers. Distrib. 17, 437–450

10 Burgess, N. et al. (2006) Factoring species, non-species values andthreats into biodiversity prioritisation across the ecoregions of Africaand its islands. Biol. Conserv. 127, 383–401

11 Armstrong, D.P. and Seddon, P.J. (2008) Directions in reintroductionbiology. Trends Ecol. Evol. 23, 20–25

Letters Trends in Ecology & Evolution January 2015, Vol. 30, No. 1

3