S. Oppel, S.J. Havery, L. John, L. Bambini, K. Varnham, J. Dawson and E. Radford Oppel, S.; S.J. Havery, L. John, L. Bambini, K. Varnham, J. Dawson and E. Radford. Maximising conservation impact by prioritising islands for biosecurity
Maximising conservation impact by prioritising islands for biosecurity
S. Oppel1, S.J. Havery1, L. John1, L. Bambini1, K. Varnham1, J. Dawson2 and E. Radford1
1Royal Society for the Protection of Birds, RSPB Headquarters, the Lodge, Sandy, Bedfordshire. SG19 2DL. U.K.
Abstract Invasive alien species are one of the primary threats to native biodiversity on islands worldwide, and their expansion continues due to global trade and travel. Preventing the arrival and establishment of highly successful invasive species through rigorous biosecurity is known to be more economic than the removal of these species once they have established. However, many islands around the world lack biosecurity regulations or practical measures and establishing biosecurity will require social and fi nancial investments. Guiding these investments towards islands where native biodiversity is at highest risk from potential invasions is of strategic importance to maximise conservation benefi t with limited resources. Here we implement an established prioritisation approach, previously used to identify which islands will have the greatest conservation gains from the eradication of invasive species, to identify which islands would benefi t the most from establishing or improving biosecurity. We demonstrate this approach for 318 islands in the Caribbean UK Overseas Territories and Bermuda where we considered all threatened native terrestrial vertebrates that are vulnerable to the most harmful invasive vertebrates (black and brown rats, cats, small Indian mongoose, green iguana). The approach calculates the increase in conservation threat score resulting from anticipated negative eff ects of potential invaders on native biodiversity, and highlighted Sombrero (Anguilla) and Cayman Brac (Cayman Islands) as important islands where threatened reptile species would likely be eliminated if rats, feral cats or mongoose invaded. Feasibility and cost implications should now be investigated more closely on the highlighted islands. The prioritisation presented here can be expanded to more islands and more invasive/native taxa (herbivores, plants and invertebrates), but requires a classifi cation of the severity of potential impacts between invasive and native species for which currently little information exists. Besides highlighting opportunities for biosecurity, this approach also highlights where knowledge gaps about population sizes of and threats to reptiles with restricted ranges exist. Keywords: Caribbean, feral cat, iguana, invasive mammals, mongoose, rats, reptiles
INTRODUCTION The majority of the world’s archipelagos have been al., 2015; Churchyard, et al., 2016), with a large number invaded by non-native species, some of which have of endemic reptiles, birds, and plants. Due to centuries detrimental eff ects on native biodiversity (Atkinson, 1985; of human habitation and inter-island trade, most islands McCreless, et al., 2016; Turbelin, et al., 2017). Although have been invaded by some non-native species (Hilton & some islands can be restored by eradicating certain invasive Cuthbert, 2010), but only a few islands contain the complete species, such operations can be expensive (Martins, et al., suite of invasive vertebrate species present in the Caribbean 2006; Holmes, et al., 2015). The limited amount of funding region. In addition, >100 small and uninhabited islands available for island restoration eff orts has motivated are still free of invasive vertebrate species and function as managers to prioritise the islands where an eradication refugia for some globally threatened species that cannot would yield the greatest biodiversity benefi ts at global and coexist with harmful invasive vertebrates (Dawson, et al., regional levels (Brooke, et al., 2007; Dawson, et al., 2015; 2015). Preventing the invasion of non-native vertebrates Stanbury, et al., 2017). However, current technologies that have caused signifi cant declines to native species on limit restoration via eradication to 15% of islands that have other islands could secure globally signifi cant populations been invaded (Keitt, et al., 2019), hence eradication is not of threatened vertebrates. Despite the recognised threat a universal solution to preserve global island biodiversity. of invasive species to endemic biodiversity, biosecurity Preventing harmful species invading those islands regulations and implementations are generally insuffi cient which still have globally signifi cant biodiversity values to reduce the risk of further spread of invasive species is an important and effi cient avenue to prevent loss of between islands in the Caribbean region (RSPB, 2017; Key biodiversity (Broome, 2007; Russell, et al., 2008; Spatz, & Moore, 2019). et al., 2017). Biosecurity measures also require fi nancial We conducted a prioritisation that identifi es those investments, both initially and in perpetuity, to detect islands where the invasion of fi ve potentially harmful and eliminate any potential invaders to islands (Oppel, invasive vertebrates could cause the greatest loss to et al., 2011; Key & Moore, 2019). Because the costs for biodiversity in the Caribbean UKOTs. We recommend biosecurity can be considerable, fi nancial constraints can immediate investment in feasibility studies and biosecurity also limit the number of islands that can be protected on those islands to avoid the invasion of these fi ve species with eff ective biosecurity measures (Moore, et al., and the subsequent loss of native biodiversity, and we 2010; Greenslade, et al., 2013). Here we propose to use recommend that similar approaches should be used in established prioritisation approaches (Brooke, et al., 2007; other regions, or indeed globally, to identify islands where Dawson, et al., 2015; Stanbury, et al., 2017) to guide investment in biosecurity is most urgently needed. the investment of resources for biosecurity to minimise the risks of invasion of non-native vertebrates to islands where they would cause the greatest loss of biodiversity. METHODS We demonstrate this approach for 318 islands that belong Study area to United Kingdom Overseas Territories (UKOTs) in the Caribbean and Bermuda. We used all 318 islands in the fi ve Caribbean UKOTs (Anguilla, British Virgin Islands, Cayman Islands, The islands in the Caribbean UKOTs feature globally Montserrat, and Turks and Caicos Islands) and in Bermuda, important biodiversity (Forster, et al., 2011; Dawson, et which is situated 1,500 km north of the Caribbean but
In: C.R. Veitch, M.N. Clout, A.R. Martin, J.C. Russell and C.J. West (eds.) (2019). Island invasives: scaling 663 up to meet the challenge, pp. 663–669. Occasional Paper SSC no. 62. Gland, Switzerland: IUCN. Island invasives: scaling up to meet the challenge. Ch 3D Strategy: Scaling up is climatically similar (Fig. 1). These islands are mostly species of conservation concern (Powell, 2004; Stephen, tropical and range from small sandy islets of 0.01 ha to et al., 2013; Vuillaume, et al., 2015). Due to the lack of islands with mountain ranges and a variety of habitat types suffi cient distribution data and limited existing knowledge > 20,000 ha. Only 14 islands are permanently inhabited of interactions, native and invasive plant or invertebrate by human communities of up to 65,000 people, while species were not considered in this prioritisation. the remaining islands are either completely uninhabited, function only as tourist resorts or destinations, or are Calculating the conservation threat score of islands visited temporarily by fi shermen. We followed the approach of Dawson, et al. (2015) to Selection of potential invasive species calculate the conservation threat score (termed ‘conservation value’ in Dawson, et al., 2015) of each island based on the To assess biodiversity loss that could result from the sum of each native species’ vulnerability. The vulnerability invasion of harmful animal species, we selected the fi ve was calculated as the product of the global threat status, most harmful invasive terrestrial vertebrates (McCreless, the irreplaceability, which indicates the global signifi cance et al., 2016) that are widespread in the Caribbean region. of an island’s population, and the severity of impact of the Green iguanas (Iguana iguana) are known to hybridise most harmful invasive vertebrate species already present and compete with native reptiles (Gibbon, et al., 2000; on an island (i.e. the species with the greatest severity of Vuillaume, et al., 2015), small Indian mongoose (Urva impact score; Dawson, et al., 2015; Stanbury, et al., 2017). auropunctata) are versatile predators considered one of the We scored threat and impact categories on both a linear and worst invasive species (Hays & Conant, 2007; Barun, et al., logarithmic scale to address the arbitrariness of assigning 2008), brown (Rattus norvegicus) and black rats (R. rattus) quantitative values to normative categories (Game, et al., and feral cats (Felis catus) are effi cient predators that can 2013; Helmstedt, et al., 2016). The severity of impact have detrimental eff ects on island biodiversity (Towns, was classifi ed in three categories, depending on whether et al., 2006; Jones, et al., 2008; Medina, et al., 2011; an invasive species had no impact on a native species (0), Nogales, et al., 2013). These fi ve species are distributed small to moderate impact that would reduce population widely across islands in the Caribbean (Kairo, et al., 2003; size but allow the native species to persist (1), or a severe Dawson, et al., 2015) and are therefore potential invaders impact that would eventually lead to the local extinction of of all islands in the region. the native species (2). We classifi ed unassessed reptiles as ‘At Risk’, which received a numerical value equivalent to Distribution of native and invasive species ‘Vulnerable’ (Dawson, et al., 2015). For each island we previously collated information on Simulating the invasion of islands to calculate increase the presence of native and invasive terrestrial vertebrate in conservation threat score species for an eradication prioritisation (Dawson, et al., 2015) and a general inventory of biodiversity (Churchyard, To quantify the magnitude of biodiversity loss that et al., 2016), and updated these previous compilations could result from invasion, we fi rst assessed which of the with recent information and threat assessments (IUCN, fi ve selected invasive species were already present on an 2017). We considered all globally threatened terrestrial island in 2016, and then simulated the arrival and invasion vertebrate species (including marine turtles) as listed on the of those species that were not yet present in 2016. We then International Union for Conservation of Nature Red List of re-calculated the conservation threat score of each island Threatened Species (IUCN, 2017) and all colonial seabird as described above, where the vulnerability of each native species and restricted range bird species. We also included species was adjusted to refl ect the most harmful invasive reptiles of conservation concern that are endemic to a single species on the island, which may be one of the simulated territory or inhabit fewer than 15 islands across their range invaders. We assumed that all invasive species not yet (Dawson, et al., 2015). We updated this information with present on an island would invade, because biosecurity new records shared by local partner organizations since measurements should, in our opinion, not be tailored for a 2013 (Hedges, 2017). We considered the green iguana that single species but guard against the arrival of a broad suite exists on Montserrat as a genetically distinct conservation of species. However, we emphasise that our prioritisation management unit, because it is genetically closely related could also be performed for single species invasions, but to the iguana on Saint Lucia, which is treated as a native assessing the merits of guarding against one or another invasive species would require information about the relative invasion risk of various species. The calculation of the conservation threat score depends on a classifi cation of the threat posed by each invasive species to each native species, but these threats can be hypothetical for interactions between certain island endemic species and invasive species that have so far not invaded the respective island. Consequently, we drew on taxonomically related or otherwise very similar species to specify the potential threat that would result from invasion. For example, if black rats adversely aff ect a small Sphaerodactylus gecko on one island, we assumed that a similarly sized Sphaerodactylus species that is endemic to an island without any rats would suff er similar eff ects if the island were invaded by rats (Case & Bolger, 1991).
Prioritising islands for biosecurity
Fig. 1 Location of 318 islands (black dots) in six United Islands that should receive the most immediate Kingdom Overseas Territories where the priority for investment into biosecurity are those where the native biosecurity was assessed. Circles around islands fauna would face the greatest increase in conservation indicate the location of the highest priority islands listed threat score if the fi ve selected vertebrate species invaded. in this paper. We therefore calculated the diff erence in conservation
664 Oppel, et al.: Prioritising islands for biosecurity value at present and after the simulated invasion of the Similar to other prioritisations identifying islands for fi ve vertebrate species, and ranked islands based on the eradication of invasive species (e.g., Harris, et al., 2012; magnitude of this diff erence. We present the results as a Dawson, et al., 2015; Stanbury, et al., 2017), our list is ranking table and include information on island size and subject to incomplete information about the distribution of human population size for each island. These aspects will both native and invasive species. The distribution of several aff ect the complexity and cost of biosecurity measures, reptile species is poorly documented across many islands as well as the probability of invasive species arrival and of the Caribbean, and their threat status is also poorly establishment, but they did not factor into our prioritisation assessed on the IUCN Red List, both of which may aff ect of islands for biosecurity, which was entirely based on the our assessment of their local importance and therefore potential threat to native biodiversity. All calculations were introduce bias to our projections of loss in conservation performed in R 3.2.5 (R Development Core Team 2015) value (Russell, et al., 2017). Further surveys to increase based on the code provided by Dawson, et al. (2015). the knowledge of native and invasive species on islands would be benefi cial but should not be used as an argument RESULTS to delay the immediate adoption of eff ective biosecurity protocols to safeguard the most important islands that we Of the 318 islands in our assessment, 125 did not have identifi ed. any invasive species on them, and 150 (47%) did not have any of the fi ve focal invasive species. Of the islands with Besides thorough knowledge about the native and any of the fi ve focal invasive species, 31 (10%) had one invasive species occurring on an island, our approach also invasive, 117 (37%) had two, 12 (4%) had three, 6 (2%) requires a classifi cation of the interactions between native had four, and only two islands (Tortola and Virgin Gorda, and invasive species. Because these interactions can be British Virgin Islands) had all fi ve of the focal invasive hypothetical for single-island endemic native species that species. On 183 islands (57.5%) the invasion of any of the have not been exposed to invasive species, due caution is fi ve focal invasive species would not lead to an increase in necessary when interpreting the output of our prioritisation. the conservation threat score, because the native vertebrates We used the response of taxonomically similar species to on these islands were not at greater risk of predation from the same invasive species to predict biologically plausible those invasive species that have not yet invaded. Thus, consequences of an invasion, but interactions between biosecurity measures to prevent the invasion of at least one native and invasive species are often complex and of the fi ve focal species would be useful on 133 islands in unpredictable (Simberloff & Von Holle, 1999; Simberloff , our assessment. 2006). We encourage researchers to provide robust and reliable predictions about the potential consequences of We identifi ed several important islands across the invasions to assist with strategic investment decisions for Caribbean UKOTs and Bermuda where biosecurity could reducing the risk of invasive species becoming established help prevent the loss of globally important biodiversity on islands harbouring globally important biodiversity (Table 1). Two islands emerged where an invasion of (Moore, et al., 2010). non-native vertebrates could lead to an increase in the conservation threat score more than fi ve times greater In summary, we demonstrated that biosecurity is not than on any other island included in our study, mostly due only important on small uninhabited islands or privately to the potential loss of Critically Endangered endemic owned tourist resorts where natural habitats remain and reptiles (Table 1): Sombrero (Anguilla), and Cayman Brac endemic and globally threatened species persist. Even (Cayman Islands). on large and populated islands such as Grand Cayman, Cayman Brac, and Montserrat, the invasion of small Among the most important islands we identifi ed for Indian mongoose could result in a signifi cant deterioration biosecurity, three were inhabited by >1000 people and of the conservation status of several globally threatened have existing populations of rats, feral cats, and green vertebrates (Hays & Conant, 2007). We therefore urge iguanas (Cayman Brac, Grand Cayman, and Montserrat, local governments, private island owners (e.g. Mosquito Table 1). However, the small Indian mongoose is so far Island) and communities to carefully inspect all incoming absent from those islands and reducing the risk of invasion cargo and people and establish ongoing measures to detect of this effi cient predator on islands that already have and remove any new invasive species. Training of border other harmful invasive species could help secure globally offi cials and conservation staff , public education and important biodiversity. Together with Montserrat, Anegada awareness campaigns targeting the accidental introduction in the British Virgin Islands was among the top priorities of invasive species onto uninhabited islands by visiting for biosecurity to reduce the risk of invasion of black rats people (e.g. fi shermen, tourists) should also be implemented, and small Indian mongoose, despite both islands also because international and domestic biosecurity measures being a high priority for the eradication of already existing are currently weak across all Caribbean UK Overseas invasive species (Dawson, et al., 2015). Territories (Key, 2017; RSPB, 2017). Laws governing biosecurity measures in the Caribbean UK Overseas DISCUSSION Territories and Bermuda are disjointed, not comprehensive and scattered through various environmental, agricultural We show that eff ective biosecurity on islands in the and customs regulations. Collaboration under existing Caribbean UK Overseas Territories could reduce the risk national legislative mechanisms may improve the situation of further spread of harmful invasive vertebrates to islands quickly prior to enacting any new legislation (RSPB, where globally threatened reptiles and birds would be at 2017). We would also encourage regional collaboration in risk. Investing in eff ective biosecurity procedures and developing biosecurity measures, information sharing and educating the public and policy makers about the risks learning from any existing biosecurity initiatives. to their national heritage when no biosecurity is in place should be the immediate next steps of UK and local ACKNOWLEDGEMENTS governments, private island owners, and international funding bodies. Our approach off ers the guidance to focus We greatly appreciate the support of all the UK Overseas on a limited number of vulnerable islands, as more than Territory governments and BirdLife International partner half of the islands we evaluated are not at immediate risk organisations for providing data on the distribution of of further biodiversity loss from the invasion of the fi ve native and invasive species. We are grateful to Montserrat invasive vertebrate species that we selected. National Trust, Anguilla National Trust, National Parks Trust of the British Virgin Islands, Turks and Caicos
665 Island invasives: scaling up to meet the challenge. Ch 3D Strategy: Scaling up sp. Ameiva corvina sp., Globally threatened species at risk from species at risk from Globally threatened invasion Sphaerodactylus acutus, Crocodylus arborea, Dendrocygna epactius, Typhlops Anolis luteosignifer, Anolis maynardii, schwartzi, Tropidophis Celestus maculatus, Cyclura nubila caymanensis Spondylurus semitaeniatus, Sphaerodactylus Amphisbaena parthenopion, Cyclura pinguis, fenestrata Ameiva corax imbricata, Chelonia mydas, Eretmochelys arborea, Dendrocygna caretta, Caretta Anolis acutus, Cyclura lewisi, Crocodylus Typhlops rhombifer, conspersus, Crocodylus caymanensis caymanensis, Tropidophis imbricata, Spondylurus Eretmochelys semitaeniatus, Spondylurus sloanii, Amphisbaena fenestrata Amphisbaena fenestrata, Sphaerodactylus imbricata, Chelonia mydas, Eretmochelys Dermochelys coriacea, Cyclura pinguis, Spondylurus anegadae cahow Pterodroma Plestiodon longirostris, threat score > 0), and only the potential new invaders are calculated as the sum of all impact scores invasive ve common vertebrate species could potentially cause the greatest increase fi Potential invaders Brown rat, black feral cat, green iguana, small Indian mongoose Brown rat, black feral cat, green iguana, small Indian mongoose Brown rat, black feral cat, green iguana, small Indian mongoose Brown rat, black feral cat, green iguana, small Indian mongoose Brown rat, black feral cat, green iguana, small Indian mongoose Black rat, small Indian mongoose Brown rat, black feral cat, green iguana, small Indian mongoose 927.5 737.6 737.0 Small Indian mongoose 244.9 242.7 210.0 204.0 5,729.2 5,514.5 Small Indian mongoose Potential in increase conservation score threat Post- invasion threat t from the removal of already existing invasive species. Human population size and island area are provided for fi 0.0 5,729.2 0.0 242.7 50.6 978.1 161.7 406.6 106.0 310.0 1,249.5 1,986.5 11,103.9 11,313.9 Current Current threat 4.1 0.0 737.6 Island (ha) area 0 49.2 0 78.2 0 1.0 200 3,844.4 2,098 3,889.4 1,364.7 6,879.3 53,160 20,159.4 Human popul’n Cayman Islands British Virgin Virgin British Islands AnguillaCayman Islands 0 Virgin British Islands Virgin British Islands Virgin British Islands Bermuda 0 8.2 The top 25 islands in Caribbean UK Overseas Territories and Bermuda where the invasion of The top 25 islands in Caribbean UK Overseas Territories in threats to native biodiversity. Note that some invasive species are already present on islands (i.e. those with current in threats to native biodiversity. species on all threatened native present an island before and after potential invasion. are listed; islands with a current threat score >0 would also bene threat scores The current and post-invasion information, as they will affect invasion risk and effort required for biosecurity. Cayman Brac Island UKOT Sombrero Anguilla 0Mosquito Island 29.2 Little Scrub Island Grand Cayman Salt Island Carval Rock Anegada Nonsuch Island Table 1 Table
666 Oppel, et al.: Prioritising islands for biosecurity Globally threatened species at risk from species at risk from Globally threatened invasion cahow Pterodroma Plestiodon longirostris, cahow Pterodroma Plestiodon longirostris, imbricata, Spondylurus Eretmochelys semitaeniatus, Amphisbaena fenestrata imbricata, Spondylurus Eretmochelys semitaeniatus, Amphisbaena fenestrata imbricata, Cyclura carinata Eretmochelys imbricata, Cyclura carinata Eretmochelys Amphisbaena Spondylurus semitaeniatus, fenestrata Dermochelys coriacea, Eretmochelys caretta, imbricata, Chelonia mydas, Caretta lherminieri, Icterus oberi, Diploglossus Turdus Anolis montisserrati, Leptodactylus fallax, lividus, Mabuya montserratae, Iguana iguana (Montserrat) Chelonia mydas, Cyclura carinata, Leiocephalus psammodromus h current threat score > 0), and only the potential new ores are calculated as the sum of all impact scores invasive ve common vertebrate species could potentially cause the greatest fi Potential invaders Brown rat, black feral cat, green iguana, small Indian mongoose Brown rat, black feral cat, green iguana, small Indian mongoose Brown rat, black feral cat, green iguana, small Indian mongoose Brown rat, black feral cat, green iguana, small Indian mongoose Brown rat, black feral cat, green iguana, small Indian mongoose Brown rat, black feral cat, green iguana, small Indian mongoose Brown rat, black feral cat, green iguana, small Indian mongoose Green iguana, small Indian mongoose Brown rat, black feral cat, green iguana, small Indian mongoose Potential in increase conservation score threat 204.0 203.3 201.3 194.4 170.4 168.4 140.3 136.8 131.7 t from the removal of already existing invasive species. Human population size and island area are provided fi Post- invasion threat 106.0 310.0 0.0 201.3 0.00.0 170.4 0.0 168.4 140.3 12571.3 12708.1 0.0 131.7 Current Current threat Island (ha) area 19.5 0.0 194.4 00 102.2 00 8.5 0 7.8 6.4 0 54.5 Human populn The top 25 islands in Caribbean UK Overseas Territories and Bermuda where the invasion of The top 25 islands in Caribbean UK Overseas Territories Bermuda 0 0.9 105.3 308.5 British Virgin Virgin British Islands Virgin British Islands and Turks Caicos and Turks Caicos Virgin British Islands and Turks Caicos (continued)
increase in threats to native biodiversity. Note that some invasive species are already present on islands (i.e. those wit increase in threats to native biodiversity. invaders are listed; islands with a current threat score >0 would also bene for information, as they will affect invasion risk and effort required for biosecurity. The current and post-invasion threat sc The current and post-invasion for information, as they will affect invasion risk and effort required biosecurity. species on all threatened native present an island before and after potential invasion. Island UKOT Horn Rock BermudaInner Pear Rock 0Ginger Island 0.3 Fallen Jerusalem Fish Cay Bush Cay Round Rock Montserrat Montserrat 4922Big Sand Cay 10157.4 Table 1 Table
667 Island invasives: scaling up to meet the challenge. Ch 3D Strategy: Scaling up Globally threatened species at risk from species at risk from Globally threatened invasion Aristelliger hechti Cyclura carinata, Aristelliger hechti Cyclura carinata, greenwayi Cyclura carinata, Tropidophis Cyclura carinata, Leiocephalus psammodromus Cyclura carinata Cyclura carinata Cyclura carinata Cyclura carinata h current threat score > 0), and only the potential new ores are calculated as the sum of all impact scores invasive ve common vertebrate species could potentially cause the greatest fi Potential invaders Brown rat, black feral cat, green iguana, small Indian mongoose Brown rat, black feral cat, green iguana, small Indian mongoose Brown rat, black feral cat, green iguana, small Indian mongoose Brown rat, black feral cat, green iguana, small Indian mongoose Brown rat, black feral cat, green iguana, small Indian mongoose Brown rat, black feral cat, green iguana, small Indian mongoose Brown rat, black feral cat, green iguana, small Indian mongoose Brown rat, black feral cat, green iguana, small Indian mongoose Potential in increase conservation score threat 123.0 123.0 121.5 117.0 111.8 111.3 110.3 110.3 t from the removal of already existing invasive species. Human population size and island area are provided fi Post- invasion threat 0.0 123.0 0.0 121.5 0.00.0 111.8 0.0 111.3 0.0 110.3 110.3 Current Current threat Island (ha) area 18.4 0.0 117.0 00 3.1 6.2 0.0 123.0 00 4.6 00 2.4 0 2.9 0 15.5 41.6 Human populn The top 25 islands in Caribbean UK Overseas Territories and Bermuda where the invasion of The top 25 islands in Caribbean UK Overseas Territories Turks and Turks Caicos and Turks Caicos Turks and Turks Caicos and Turks Caicos and Turks Caicos and Turks Caicos and Turks Caicos and Turks Caicos y increase in threats to native biodiversity. Note that some invasive species are already present on islands (i.e. those wit increase in threats to native biodiversity. invaders are listed; islands with a current threat score >0 would also bene for information, as they will affect invasion risk and effort required for biosecurity. The current and post-invasion threat sc The current and post-invasion for information, as they will affect invasion risk and effort required biosecurity. species on all threatened native present an island before and after potential invasion. IslandSix Hills East UKOT Ca Six Hills Cay West Middleton Cay Long Cay (Turks) White Cay Indian Cay Plandon Cay Middle Creek Cay Table 1 (continued) Table
668 Oppel, et al.: Prioritising islands for biosecurity
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