Prioritising islands in the United Kingdom and crown dependencies for the eradication of invasive alien vertebrates and rodent biosecurity

Invasive alien vertebrates (IAVs) pose a significant threat to island biodiversity worldwide, and their removal is an important nature conservation management goal. As methods advance, eradications from larger islands and of multiple species simultaneously are increasingly undertaken. Effective targeting to maximise conservation gain is important given limited resources. We build on existing prioritisation methods and use the islands of the UK and Crown Dependencies (UK) as an example of how vertebrate eradications might be prioritised and invasive-free status maintained through biosecurity. For each of the 9688 UK islands, we assessed ecological importance for native vertebrates and the anticipated impacts of the IAVs present to estimate the benefit of restoration based on the feasibility and sustainability of IAV eradications in relation to island size, human population and risk of unassisted reinvasion by swimming. As reinvasion poses a threat to the long-term benefits of eradication, we incorporated species-specific swimming distances and explored the effects of varying reinvasion probability from risk-averse to higher-risk strategies. The 25 islands that would benefit most from eradications were in Scotland, Northern Ireland and the Channel Islands. Our prioritisation method should be seen as an initial guide to identify islands that might benefit from intervention when faced with a large list of potential sites. Feasibility studies taking account of factors such as interspecific interactions, anthropogenic reinvasion, views of residents or ‘social feasibility’ and cost need to be undertaken before planning any eradication. We prioritised biosecurity for rat-free islands to highlight where comprehensive measures might be most beneficial.     

Review article: The catastrophic impact of invasive mammalian predators on birds of the UK Overseas Territories: a review and synthesis

The UK has sovereignty over 16 Overseas Territories, which hold some of the world’s great seabird colonies and collectively support more endemic and globally threatened bird species than the whole of mainland Europe. Invasive alien mammalian predators have spread throughout most of the Territories, primarily since European expansion in the 16th century. Here we review and synthesize the scale of their impacts, historical and current, actions to reduce and reverse these impacts, and priorities for conservation. Mammalian predators have caused a catastrophic wave of extinctions and reductions in seabird colony size that mark the UKOTs as a major centre of global extinction. Mammal‐induced declines of threatened endemics and seabird colonies continue, with four Critically Endangered endemics on Gough Island (Tristan da Cunha), St Helena and Montserrat directly threatened by invasive alien House Mice Mus musculus, Feral Cats Felis catus and rats Rattus spp. Action to reduce these threats and restore islands has been modest in comparison with other developed countries, although some notable successes have occurred and a large number of ambitious eradication and conservation plans are in preparation. Priority islands for conservation action against mammalian predators include Gough (which according to one published prioritization scheme is the highest‐ranked island in the world for mammal eradication), St Helena and Montserrat, but also on Tristan da Cunha, Pitcairn and the Falkland Islands. Technical, financial and political will is required to push forward and fund the eradication of invasive mammalian predators on these islands, which would significantly reduce extinction risk for a number of globally threatened species.     

Non-intrusive systematic study reveals mutualistic interactions between threatened island endemic species and points to more impactful conservation

Oceanic islands harbour a disproportionately large share of extinct and endangered birds worldwide and up to about 6,800 highly threatened plants, stressing the urgency for conservation efforts there. However, effective conservation action can only be as sound as the ecological understanding on which it is based. Knowledge about the ecology of threatened birds and plants can be relatively sketchy even in well-studied oceanic islands and this can potentially misdirect or erode conservation actions’ effectiveness. We used camera traps to document vertebrate flower visitors of a threatened, mono-specific endemic oceanic island plant (Roussea simplex) that produces much nectar and which was abundant until the 1930s before declining severely despite its presence mostly within protected areas. We determined proportions of native and alien flower visitors in four populations and characterised their ecological role (e.g. florivore, nectar robber, pollinator) through observations and exclusion experiments alongside experiments to determine seed sets by agamospermy, autogamy, geitonogamy and xenogamy. Five native and three alien vertebrate species visited flowers (N = 5,085 camera trap-hours), 96.6% of visits being from birds. Among endemics, 74–96% of visits were by the Mauritius Bulbul (Hypsipetes olivaceus), a threatened bird able to effect pollination contrary to the other endemic birds. Roussea simplex is primarily xenogamous, producing 2,657 ± 480 seeds, and seed set dropped markedly when the bird was excluded (861.8 ± 91.0 SE, Kruskal-Wallis χ² = 14.2, p < 0.001). Natural seed set was very low (410.0 ± 85.3 SE) where the bird was locally extinct or very rare. Invasive alien rats (Rattus rattus) and long-tailed macaques (Macaca fascicularis) were important florivores or nectar robbers. Systematic non-intrusive study using camera traps combined with manipulative experiments revealed a mutualism between two relatively well-studied threatened endemic species as well as new threats from alien vertebrates acting as nectar robbers and florivores. Roussea simplex’s major decline within protected areas and its abundant and year round flowering and nectar production point to a major hitherto unrecorded drop in floral resource previously available to at least five endemic species, and particularly to its commonest flower visitor and principal pollinator, the threatened Mauritius Bulbul. These findings exemplify how systematic non-intrusive study of threatened species may radically change conservation managers’ priorities which in the current case should focus primarily on controlling alien rats and macaques and re-instating or reinforcing Bulbul-Roussea mutualism as each would be more impactful than addressing gecko-Roussea mutualism disruption by alien ants which so far was the only recorded threat thought to drive the rapid decline of Roussea simplex. Our study underscores that current conservation efforts should also pay particular attention to medium to longer-term changes in habitat or community composition which may not be obvious from merely considering extent and composition of current habitats.     

Restoration of a tropical island: Cousine Island,Seychelles

Tropical island species and ecosystems are threatened worldwide as a result of increasing human pressure. Yet some of these islands also lend themselves to restoration, as they are physically defined units that can be given focused attention, as long as resources are available and clear conservation targets are set. Cousine Island, Seychelles, is a tropical island that has received such intensive restoration. From a highly degraded island in the 1960s, the island has now been restored to what is believed to be a semblance of the natural state. All alien vertebrates have been eradicated, as have 25 invasive alien plants. Cultivated plants are now confined to one small section of the island. Poaching of nesting marine turtles has been stopped, leading to an increase in turtle breeding numbers. The shearwater population has increased in size with poaching activities under control. The Sooty tern has also returned to the island to breed. The coastal plain has been restored with over 2,500 indigenous shrubs and trees, which have now grown into a forest carpet. There are strict quarantine procedures on the island, keeping it free of rats, mice, various alien invertebrates and potentially invasive alien plants. Three threatened Seychelles endemic land birds (Seychelles warbler, Seychelles magpie robin and Seychelles white-eye) have been introduced and are thriving, with these introductions contributing to both the magpie robin and the white-eye being downgraded from CR to EN (the warbler remains at VU). Ecotourism, and nature conservation for the local inhabitants, have been introduced in a way that does not reduce the improved compositional, structural and functional biodiversity of the island. The result of the restoration effort appears to be sustainable in the long term, although challenges still remain, especially with regards to adequate clean water and a non-polluting power supply on the island. Cousine is thus paving the way in the art and science of tropical island restoration as a legacy for future generations.     

A global review of the impacts of invasive cats on island endangered vertebrates

Cats are generalist predators that have been widely introduced to the world's ~179 000 islands. Once introduced to islands, cats prey on a variety of native species many of which lack evolved defenses against mammalian predators and can suffer severe population declines and even extinction. As islands house a disproportionate share of terrestrial biodiversity, the impacts of invasive cats on islands may have significant biodiversity impacts. Much of this threatened biodiversity can be protected by eradicating cats from islands. Information on the relative impacts of cats on different native species in different types of island ecosystems can increase the efficiency of this conservation tool. We reviewed feral cat impacts on native island vertebrates. Impacts of feral cats on vertebrates have been reported from at least 120 different islands on at least 175 vertebrates (25 reptiles, 123 birds, and 27 mammals), many of which are listed by the International Union for the Conservation of Nature. A meta‐analysis suggests that cat impacts were greatest on endemic species, particularly mammals and greater when non‐native prey species were also introduced. Feral cats on islands are responsible for at least 14% global bird, mammal, and reptile extinctions and are the principal threat to almost 8% of critically endangered birds, mammals, and reptiles.     

Historical bird and terrestrial mammal extinction rates and causes

Aim Conservation of species is an ongoing concern. Location Worldwide. Methods We examined historical extinction rates for birds and mammals and contrasted island and continental extinctions. Australia was included as an island because of its isolation. Results Only six continental birds and three continental mammals were recorded in standard databases as going extinct since 1500 compared to 123 bird species and 58 mammal species on islands. Of the extinctions, 95% were on islands. On a per unit area basis, the extinction rate on islands was 177 times higher for mammals and 187 times higher for birds than on continents. The continental mammal extinction rate was between 0.89 and 7.4 times the background rate, whereas the island mammal extinction rate was between 82 and 702 times background. The continental bird extinction rate was between 0.69 and 5.9 times the background rate, whereas for islands it was between 98 and 844 times the background rate. Undocumented prehistoric extinctions, particularly on islands, amplify these trends. Island extinction rates are much higher than continental rates largely because of introductions of alien predators (including man) and diseases. Main conclusions Our analysis suggests that conservation strategies for birds and mammals on continents should not be based on island extinction rates and that on islands the key factor to enhance conservation is to alleviate pressures from uncontrolled hunting and predation.     

Costing eradications of alien mammals from islands

The ability to estimate costs of alien species eradications is essential for a rigorous assessment of priorities for island restoration. Using a global data file from 41 islands, mostly gleaned from the 'grey' literature, we show that the cost of vertebrate eradications can be satisfactorily predicted if island area and species to be eradicated are known. About 72% of the variation in cost can be explained by island area, whereas, for a given area, rodent eradications are 1.7–3.0 times more expensive than ungulate eradications. Costs per hectare decrease with island size. Restricting the analysis to roughly half the data set, the relatively homogeneous half concerned with New Zealand islands, we identify two further influences on cost: date of eradication and distance to the main airport (an indicator of remoteness). For a given area, costs have declined over time but increase with island remoteness. This information therefore provides conservation planners with a robust, if preliminary, estimate of the cost of any proposed eradication programme.     

Trophic niche changes associated with the eradication of invasive mammals in an insular lizard: an assessment using isotopes

Invasive species are a major threat to island biodiversity, and their eradications have substantially contributed to the conservation of island endemics. However, the consequences of eradications on the trophic ecology of native taxa are largely unexplored. Here, we used the eradication of invasive black rats Rattus rattus and European rabbits Oryctolagus cuniculus from the Berlenga Island, in the western coast of Portugal, as a whole-ecosystem experiment to investigate the effects of the eradication of invasive mammals on the trophic niche and body dimensions of the island-restricted Berlenga wall lizard Podarcis carbonelli berlengensis over a 2-year period. Our results suggest an expansion of the isotopic niche and an intensification of the sexual dimorphism of the lizard following mammal eradication. Additionally, we found considerable variability in isotopic niche across the island and detected evidence of sex-specific and season-modulated nutritional requirements of this threatened reptile. Our findings support that the eradication of 2 of the planet’s most problematic invasive vertebrates led to changes in the lizard trophic niche and sexual dimorphism in just 2 years. This suggests that the ecological pressures—for example, prey availability and habitat structure—to which lizards are exposed have substantially changed post-eradication. Our study emphasizes the scientific value of island eradications as experiments to address a wide range of ecological questions and adds to the increasing body of evidence supporting substantial conservation gains associated with these restoration interventions.     

Integrating seabird restoration and mammal eradication programs on islands to maximize conservation gains

Colonial nesting seabirds frequently drive island ecosystem biodiversity by maintaining ecosystem functioning and community dynamics. Invasive mammal introductions to most of the world’s islands have ravaged insular seabird populations and had associated devastating ecosystem-wide effects. Eradication programs remove invasive mammals from islands, with the goal of conserving and restoring island species and systems. However, most eradication programs rely almost exclusively on passive seabird recovery to achieve these goals. Unfortunately, the life histories of most seabird species are not conducive to passive recovery within a contemporary timeframe. Seabird restoration techniques can effectively overcome life history related issues and significantly reduce recovery times for insular seabird populations, thereby reducing associated ecosystem-wide recovery times. By integrating seabird restoration and eradication programs, practitioners can maximize conservation gains, expand funding opportunities, and restore island ecosystems and the biodiversity they support.     

Conservation of native fauna in highly invaded systems: managing mammalian predators in New Zealand

Programs to conserve native fauna in invaded ecosystems often aim to reduce the impacts of alien predators. This approach can lead to unexpected outcomes in the native and the remaining invasive components of restored ecosystems. In New Zealand, suppression and eradication of invasive mammalian predators are well‐established conservation strategies, particularly on offshore islands and in mainland ecosanctuaries. Predator control has achieved important conservation gains over increasingly large areas but these can be offset by the ecological release of other uncontrolled pest species. In addition, novel ecosystems created by selective predator control and reintroductions of locally extinct or depleted native species may have unexpected trajectories as they evolve. Effective conservation requires new techniques for controlling entire suites of invasive predators over large areas, routine monitoring of the conservation outcomes of predator control, and better understanding of how modified, and in some cases reconstructed, seminatural ecosystems change when invasive predators are removed.     

Accomplishments and impact of the NGO,Island Conservation,over 15 years (1994–2009)

Improvements in biodiversity conservation are hampered by the lack of reporting on the effectiveness of conservation techniques and the organizations that implement them. Here we summarize the accomplishments and potential impact of the non-governmental organization, Island Conservation, which eradicates damaging invasive vertebrates from islands. Island Conservation has removed 54 populations of 10 invasive vertebrates from 35 islands totaling over 520 km². These actions helped protect 233 populations of 181 insular endemic species and subspecies of plants and vertebrates and 258 populations of 54 species and subspecies of seabirds from the threat of local and global extinction. There were no reinvasions. One eradication attempt failed. These conservation actions and their apparent biodiversity impact demonstrate the potential of private organizations to protect biodiversity by eradicating invasive species from islands.     

Integrating invasive mammal eradications and biodiversity offsets for fisheries bycatch: conservation opportunities and challenges for seabirds and sea turtles

The removal of invasive mammals from islands is one of society’s most powerful tools for preventing extinctions and restoring ecosystems. Given the demonstrable high conservation impact and return on investment of eradications, new networks are needed to fully leverage invasive mammal eradications programs for biodiversity conservation at-large. There have been over 800 invasive mammal eradications from islands, and emerging innovations in technology and techniques suggest that island area will soon no longer be the limiting factor for removing invasive mammals from islands. Rather, securing the necessary social and economic capital will be one main challenge as practitioners target larger and more biologically complex islands. With a new alliance between conservation practitioners and the fisheries sector, biodiversity offsets may be a promising source of capital. A suite of incentives exists for fisheries, NGOs, and governments to embrace a framework that includes fishery bycatch offsets for seabirds and sea turtles. A bycatch management framework based on the hierarchy of “avoid, minimize, and offset” from the Convention on Biological Diversity would result in cost-effective conservation gains for many threatened seabirds and sea turtles affected by fisheries. Those involved with island conservation and fisheries management are presented with unprecedented opportunities and challenges to operationalize a scheme that will allow for the verifiable offset of fisheries impacts to seabirds and sea turtles, which would likely result in unparalleled marine conservation gains and novel cross-sector alliances.     

Inseln: Ursprung der Vielfalt

The theory of island biogeography was originally developed to evaluate the influence of island size and distance from mainland on their number and composition of species. Meanwhile, this theory has become an important tool for nature conservation strategies. Due to various reasons, organisms arriving at islands are tending along their evolution to develop dwarf of giant forms. Although islands are constantly emerging and decaying, they are representing a constant phenomenon on earth, and therefore have a particular importance for evolutionary processes. Today, genetic analyses have archived importance in the disentanglement of colonisation processes of islands. Furthermore, islands often represent localities with high proportions of endemic species, which are increasingly threatened through the invasion of alien species.     

Eradicating multiple invasive species on inhabited islands: the next big step in island restoration?

Invasive species are the greatest threat to island ecosystems, which harbour nearly half the world’s endangered biodiversity. However, eradication is more feasible on islands than on continents. We present a global analysis of 1,224 successful eradications of invasive plants and animals on 808 islands. Most involve single vertebrate species on uninhabited islands, but plant and invertebrate eradications occur more often on inhabited islands. Inhabited islands are often highly modified and support numerous introduced species. Consequently, targeting a single invasive species can be ineffective or counterproductive. The impacts of other pests will continue and, in some cases, be exacerbated. The presence of people also creates regulatory, logistical and socio-political constraints. Real or perceived health risks to inhabitants, pets and livestock may restrict the use of some eradication tools, and communities or individuals sometimes oppose eradication. Despite such challenges, managing invasive species is vital to conserve and restore the unique biodiversity of many inhabited islands, and to maintain or improve the welfare and livelihoods of island residents. We present a brief case study of the Juan Fernández Archipelago, Chile, and discuss the feasibility of eradicating large suites of invasive plants and animals from inhabited islands while managing other invaders for which eradication is not feasible or desirable. Eradications must be planned to account for species interactions. Monitoring and contingency plans must detect and address any ‘surprise effects’. Above all, it is important that the local community derives social, cultural and/or economic benefits, and that people support and are engaged in the restoration effort.     

Invasive plant species in the West Indies: geographical,ecological, and floristic insights

The level of invasion (number or proportion of invasive species) in a given area depends on features of the invaded community, propagule pressure, and climate. In this study, we assess the invasive flora of nine islands in the West Indies to identify invasion patterns and evaluate whether invasive species diversity is related to geographical, ecological, and socioeconomic factors. We compiled a database of invasive plant species including information on their taxonomy, origin, pathways of introduction, habitats, and life history. This database was used to evaluate the similarity of invasive floras between islands and to identify invasion patterns at regional (West Indies) and local (island) scales. We found a total of 516 alien plant species that are invasive on at least one of the nine islands studied, with between 24 to 306 invasive species per island. The invasive flora on these islands includes a wide range of taxonomic groups, life forms, and habitats. We detected low similarity in invasive species diversity between islands, with most invasive species (>60%) occurring on a single island and 6% occurring on at least five islands. To assess the importance of different models in predicting patterns of invasive species diversity among islands, we used generalized linear models. Our analyses revealed that invasive species diversity was well predicted by a combination of island area and economic development (gross domestic product per capita and kilometers of paved roadways). Our results provide strong evidence for the roles of geographical, ecological, and socioeconomic factors in determining the distribution and spread of invasive species on these islands. Anthropogenic disturbance and economic development seem to be the major drivers facilitating the spread and predominance of invasive species over native species.     

Going Cheap: Determinants of Bird Price in the Taiwanese Pet Market

BackgroundInternational wildlife trade is the largest emerging source of vertebrate invasive alien species. In order to prevent invasions, it is essential to understand the mechanics of trade and, in particular, which traded species are most likely to be released or escape into the wild. A species’ economic value is a key factor, because we expect cheaper species to be less assiduously secured against escaping, and more likely to be deliberately released. Here, we investigate determinants of the price of species in the Taiwanese bird trade. Taiwan is an international hub for bird trade, and several native species are threatened by alien bird species.MethodologyWe investigated the relationship between the traded species sale price in Taiwan and the species availability for trade (the number of birds for sale, geographic range size and their origin, conservation and CITES status) and traits (body size, coloration, song attractiveness). We used phylogenetic generalized least squares models, with multi-model inference, to assess the variables that are best related to the price of birds in the Taiwanese pet trade.

Principal Findings / Conclusions

We found that species available for sale in larger numbers, native to Taiwan, not globally endangered, and small-bodied are all relatively cheaper, as too are species lacking yellow coloration and without attractive songs. Our models of price revealed high levels of phylogenetic correlation, and hence that closely related species tended to be sold for similar prices. We suggest that, on the basis of price, native species are more likely to be deliberately or accidentally released than alien species. Nevertheless, our survey of bird shops recorded 160 species alien to Taiwan (7,631 individuals), several of which are for sale cheaply and in large numbers. Alien bird species in trade therefore present an ongoing, non-trivial invasion risk on the island.     

The biodiversity of the United Kingdom’s Overseas Territories: a stock take of species occurrence and assessment of key knowledge gaps

Limited financial resources for conservation and growing environmental problems make it vital to base conservation on sound scientific evidence. Small islands hold a disproportionately large amount of the worlds threatened biodiversity but it is among the least well-documented. This paper reports on the most extensive collation and synthesis of biodiversity data to date for the 14 United Kingdom Overseas Territories (UKOTs). A process of literature review and consultation produced 65,259 species records, including 32,216 native species of which 1549 were endemic to a single UKOT. The extent of knowledge of species occurrence varied both between islands and taxonomic groups. It was higher for vertebrates and vascular plants than small bodied invertebrates and non-vascular and for non-Caribbean compared to Caribbean islands, a difference that largely reflects knowledge of invertebrates. Global Red List assessments exist for 2606 species and document 111 of endemic species, 75 % of those assessed, and 291, 12 % of non-endemics, as globally threatened. Using the data to estimate true species richness suggests a further 70,000 native species, including 1800 single island endemics, remain to be documented suggesting the UKOTs as a whole may support over 100,000 native species including 3300 single island endemics.     

A global review of island endemic birds

Although fewer than one-fifth of the world's bird species are restricted to islands, over 90% of bird extinctions during historic times have occurred on islands. The major identified cause has been the effects of exotic animal species introduced by man; the largest number of documented extinctions has occurred on islands of the Pacific Ocean.
Some 39% (402) of threatened bird species are restricted to islands and more than 907; of these are endemic to a single geopolitical unit. The largest numbers occurring in such units are in Indonesia (91) and the Philippines (34). As a region, the Pacific holds more threatened species (110) than any other, including almost half of those considered Endangered and over 40% of the Vulnerable species.
Most threatened island species are forest-dwelling. A high proportion of the Endangered species use seasonal/temperate forest. While habitat destruction now poses the greatest overall threat to island birds (affecting over half the species restricted to islands), the presence of introduced species threatens 30 of the 66 Endangered species.
Although immediate extinctions of island species can best be averted by mitigating the effects of introductions, the removal of native forests will be a more severe problem in the longer term. There is an urgent need for ecologists to provide detailed information on the habitats of both threatened and endemic species so that more appropriate and effective conservation programmes can be developed.     

Preliminary conservation status and needs of an oceanic island fauna: the case of Seychelles insects

Islands are generally reported to have much higher extinction rates and levels of threat than continental areas. This perception is based largely on studies of vertebrates. A recent assessment of the biodiversity of the Seychelles islands enables the status of a range of taxonomic groups to be compared. A high proportion of the fauna is found to be threatened, with Dictyoptera being the most threatened insect order (51% of 34 native species) followed by Orthoptera (47% of 68 species). Lower levels of threat are found in Diptera (28% of 562 species), Dermaptera (24% of 21 species) and Lepidoptera (21% of 517 species). Differences between the orders relate mainly to distribution patterns, with the most threatened orders having the highest proportions of endemic and restricted range species. The main threats for most orders are habitat deterioration due to invasion by introduced plant species, sea level rise and climate change. These threat factors are different from those reported to affect vertebrates, which are generally considered to be threatened by introduced predators resulting in critically low population sizes. These findings indicate that conservation sources would be more useful and cost effective for insect conservation if directed to habitat maintenance and restoration rather than to alien predator control.     

The role played by invasive species in interactions with endangered and threatened species in the United States: a systematic review

Invasive species are considered to be a leading cause of the decline of threatened species. However, this view has been disputed because much of the evidence base is anecdotal. This systematic review, through an extensive, repeatable search using agreed selection criteria, examined the available scientific evidence on invasive species’ interactions with the 1363 endangered and threatened species protected under the United States Endangered Species Act (ESA). The review found scientific evidence available for 116 endangered or threatened species (8.5% of the ESA list). Of these, 85 species (6.2%) were reported as being negatively impacted by invasive species: 39 located on the continental US and 39 on islands, with seven marine species. The relative percentages of species impacted differed according to location: 4.3% (n?=?906) on the continental US, 9.3% (n?=?420) on islands. It was found that predation by invasive vertebrates on birds on islands and competition between invasive plants and endangered or threatened plants on the mainland were the main mechanisms of impact. The results of this study contrast markedly with a previous study which found that 49% of imperilled species in the United States were threatened by invasive species. Further research is essential in order to evaluate the impact of invasive species on imperilled species on the ESA list; this would help to reduce the high degree of uncertainty regarding the threat of invasive species due to the lack of empirical information.