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Eradications as reverse invasions: Lessons from Pacific rat (Rattus exulans) removals on New Zealand islands
Abstract
Eradications of kiore or Pacific rats (Rattus exulans) from islands around New Zealand have been followed by responses from resident species of coastal plants, invertebrates,
reptiles and seabirds. These responses are compared with an invasion by ship rats (Rattus rattus), which devastated populations of invertebrates, birds and bats. Post-eradication responses only approximate the effects
of invasions because recovery is limited to the residual pool of native species. Greater effects of kiore are indicated by
adding incompatible species confined to rat-free locations. The extended list includes at least 15 species of invertebrates,
two species of frogs, tuatara (Sphenodon punctatus), 11 species of lizards and 9 species of seabirds. The analyses indicate direct and indirect effects of kiore similar to
those reported after ship rat invasions. This is despite indications from the literature that kiore are the least damaging
of the three commensal rat species.
... Four species of invasive rodents are present in NZ. Pacific rat or kiore (Rattus exulans) arrived first with Polynesian settlers in the early 13th century; they have ongoing impacts on native flora and fauna that did not evolve with rats (Towns, 2009). Norway rats (R. norvegicus) arrived during the 18th century on European ships, and house mice (Mus musculus; hereafter mouse or mice) and ship rats (R. rattus) a century later (Veale et al., 2018). ...
... Beyond a small survey of 19 stakeholders (Tompkins, 2018), there is no published account of the process by which possums, rats, and mustelids were chosen. For example, while kiore are included in the goal, this species has localized ecological effects and has cultural significance in some areas (Towns, 2009), whereas mice arguably have a more significant impact at a national scale, a concern that was noted by ecosanctuary survey participants at the time. A robust analysis of the species for inclusion in such a significant national initiative could have considered multidimensional political, social (Liang, 2023), cultural, and financial aspects of the campaign as well as the practical aspects of planning for eradication, ensuring that the consequences of eradicating select species are evaluated. ...
Predator Free 2050 (PF2050) is a government initiative aiming to eradicate selected invasive mammals (mustelids, rats, and possums) from New Zealand (NZ) by 2050. Selecting which of 32 introduced mammal species to include has received little evaluation, yet targeting a few species often results in perverse ecological outcomes given interactions within the invasive guild. We explore how PF2050 could be improved strategically by focusing on biodiversity outcomes instead of selectively targeting invasives, using rodents as an example. Current PF2050 targets include all rat species ( Rattus exulans , R. norvegicus , and R. rattus ), but not the house mouse ( Mus musculus ). Mice can be as damaging as rats when competition and predation are removed, negating benefits of rat removal. Multirodent eradications are more cost‐effective and prevent mesopredator release. Using a case study, we show adding mice to a rat eradication would raise costs modestly, comparing favorably to independent mouse eradication later, which would be riskier and more socially and economically costly than the preceding rat eradication. Missing the opportunity to tackle all rodents simultaneously, leaving mice to multiply in numbers and impacts, could have serious environmental and socioeconomic consequences. Naïve eradication strategies neglecting ecological expertise risk biodiversity outcomes and NZ's eradication science reputation.
... Introduced predators in particular can have dramatic impacts on native biota, especially on islands where the native fauna has evolved in the absence of such predators (Savidge 1987;Lodge 1993;Medina et al. 2011). In New Zealand where native terrestrial fauna has evolved in the absence of mammals (except bats), introduced mammalian predators have caused impacts ranging from behavioural shifts (Hoare et al. 2007) to population declines and extinctions of native fauna (Atkinson & Cameron 1993;Towns & Daugherty 1994;Towns et al. 2001;Towns et al. 2006;Towns 2009). In response to this threat, predator control or eradication has been widely implemented as a management strategy (Towns et al. 2001;Towns et al. 2006;Towns 2009;Brown et al. 2015). ...
... In New Zealand where native terrestrial fauna has evolved in the absence of mammals (except bats), introduced mammalian predators have caused impacts ranging from behavioural shifts (Hoare et al. 2007) to population declines and extinctions of native fauna (Atkinson & Cameron 1993;Towns & Daugherty 1994;Towns et al. 2001;Towns et al. 2006;Towns 2009). In response to this threat, predator control or eradication has been widely implemented as a management strategy (Towns et al. 2001;Towns et al. 2006;Towns 2009;Brown et al. 2015). Such predator control programs can have dramatic benefits for native fauna, although effects may be variable among native taxa (Towns et al. 2006), precise mechanisms of impact may be difficult to identify (Towns et al. 2006), and indirect effects may make it difficult to predict all ecological consequences (Tompkins & Veltman 2006). ...
... The flax weevil is one of the few insect species that is fully protected under the Wildlife Act 1953 (Miskelly 2014), and is dependent on flax plants (Phormium spp.) for its survival during all stages of its life cycle; the adult beetles feed on flax leaves, while larvae develop underground, feeding on and within flax rhizomes (Gourlay 1931). Due to predation by introduced mammals, populations of flax weevil persist only on predator-free islands or in alpine areas, which can be remote and difficult to access for research purposes (Gibbs 2009;Towns 2009). ...
... The largest and most ecologically diverse islands of this region are those of New Zealand, which were settled in the mid-13th Century C.E. 13 . Habitat change, introduced species, and hunting following the arrival of Polynesian colonists in New Zealand transformed ecosystems and their services to nature 14,15 , giving rise to one of the largest and most rapid collapses of native biota in the Paci c 16, 17 . Included among New Zealand's lost species were enormous raptors 16 , unique ightless species 18 , and giant wingless birds called moa (Dinornithiformes) 19 . ...
Human settlement of islands across the Pacific Ocean was followed by waves of faunal extinctions that occurred so rapidly that their dynamics are difficult to reconstruct in space and time. These extinctions included large, wingless birds endemic to New Zealand called moa. We reconstructed the range and extinction dynamics of six genetically distinct species of moa across New Zealand at a fine spatiotemporal resolution, using hundreds of thousands of process-explicit simulations of climate-human-moa interactions, which were validated against inferences of occurrence and demographic change from an extensive fossil record. This statistical-simulation analysis revealed important interspecific differences in the ecological and demographic attributes of moa that influenced the timing and pace of their geographic and demographic declines following colonization of New Zealand by Polynesians. Despite these interspecific differences in extinction dynamics, the spatial patterns of geographic range collapse of moa species were similar. The final populations of all moa species persisted in suboptimal habitats in cold, mountainous areas that were generally last and least impacted by people. These isolated refugia for the last populations of moa continue to serve as sanctuaries for New Zealand’s remaining flightless birds, providing novel insights for conserving endemic species in the face of current and future threats.
... As kiore are trapped and removed from islands across the Pacific and in Aotearoa, it has become clear that kiore eradication is not universally supported. Kiore can have important deleterious consequences for ecosystems, for example, as seed eaters and predators of seabird chicks (Towns, 2009). However, in some parts of New Zealand, kiore remain highly valued, as a customary food, for its skin, and as an ecological indicator (Wehi, Wilson, et al., 2021). ...
Introduced species that spread and become invasive are recognised as a major threat to global biological diversity, ecosystem resilience and economic stability. Eradication is often a default conservation management strategy even when it may not be feasible for a variety of reasons. Assessment of the substantive socioeconomic and ecological impacts of invasive alien species (IAS), both negative and positive, is increasingly viewed as an important step in management.
We argue that one solution to IAS management is to align models of alien species management with Indigenous management frameworks that are relational and biocultural. We make the theoretical case that centring Indigenous management frameworks promises to strengthen overall management responses and outcomes because they attend directly to human and environmental justice concerns.
We unpack the origins of the ‘introduced species paradigm’ to understand how binary framing of so‐called ‘aliens’ and ‘natives’ recalls harmful histories and alienates Indigenous stewardship. Such a paradigm thereby may limit application of Indigenous frameworks and management, and impede long‐term biodiversity protection solutions.
We highlight how biocultural practices applied by Indigenous Peoples to IAS centre protecting relationships, fulfilling responsibilities and realising justice.
Finally, we argue for a pluralistic vision that acknowledges multiple alternative Indigenous relationships and responses to introduced and IAS which can contribute to vibrant futures where all elements of society, including kin in the natural world, are able to flourish.
Read the free Plain Language Summary for this article on the Journal blog.
... The role played by introduced mammalian predators in causing the decline and/or extinction of many of Aotearoa's indigenous species is well documented, particularly for birds (Innes et al. 2010), but also lizards (Reardon 2012) and invertebrates (Bremner et al. 1984;Towns 2008;O'Donnell et al. 2017). In the 1970s and 1980s recognition of the extreme vulnerability to predation of deep endemic bird and reptile taxa resulted in heavy emphasis on the conservation value of predatorfree offshore islands (Towns et al. 2012). ...
... Multiple cervid species, the European rabbit, hare, and red fox (Vulpes vulpes) were imported to Australia and several of these also soon arrived in New Zealand (Krull et al. 2014). Shipping and human movement also facilitated commensal rodent-island hopping, which has been catastrophic for some bird species across Oceania's islands (Matisoo- Smith and Robins 2008;Towns 2009). Livestock competing for resources, and game species that became invasive in Australia and New Zealand, has impacted the bulk of the continent's landmass and consequently its native wildlife. ...
The need to identify interactions with the potential for pathogen transmission among the community of hosts at the wildlife–livestock interface has led to the development of multiple approaches in the field of epidemiology. Methodologies can be broadly classified into those that allow the quantification of interactions and those whose objective is to detect the existence of potential interactions at the interface. Regardless of their capacity to quantify or detect this potential, it is possible to study both direct (i.e., the simultaneous presence of two individuals at a certain point) and indirect (i.e., the sequential presence of two individuals at a certain point) interactions. Although each methodology has its specific pros and cons, when individuals are not marked, the main limitations are the difficulty involved in assessing the spatio-temporal resolution of events and, obviously, the role played by the individuals involved, the nature of the interaction, and the associated level of epidemiological risk. Furthermore, marking a limited number of individuals with different devices (e.g. GPS, proximity loggers) normally implies the possibility of low representativeness of the target population, especially when high variability exists in behaviour and connectedness of individual animals. The present chapter reviews the methodologies most commonly used to collect the data employed to assess interactions at the wildlife–livestock interface, namely, the direct observation of animals, epidemiological sampling, epidemiological questionnaires, camera traps, GPS technology, and proximity loggers. We also present the complementary nature of different methodologies by means of a specific case study of animal tuberculosis in the Iberian Peninsula. The methods selected have to adapt to the objectives of the study, logistic constraints, target host species and pathogens, and the routes of transmission at the wildlife/livestock interface.
... One novel biotic interaction that predominates across many islands is seed predation by introduced animals, including rodents, birds, and insects. For example, non-native rodents have been introduced on >80 % of islands globally (Towns, 2009) and predate seeds of a wide range of plant species, often at very high levels (Chimera and Drake, 2011;Shiels and Drake, 2011;Wotton and Kelly, 2011). Although introduced rodents can occasionally disperse seeds, they are by and large seed predators (Hays et al., 2018;Shiels and Drake, 2011). ...
... Conservation concerns refer primarily to the detrimental effects caused by rats on plants and animals they consume but also to the cascading top-down indirect effects over the entire insular ecosystem, e.g., through interruption of pollination, nutrient pathways, or seed predation Towns 2009;Auld et al. 2010;Grant-Hoffmann and Barboza 2010;Graham et al. 2018). The negative effects on seabird populations, for instance, which are mediated by predation on eggs, chicks or adults of several species globally (Jones et al. 2008), reduce the marine-terrestrial subsidy brought by seabirds to islands (Benkwitt et al. 2021). ...
Invasive predators on islands impact organisms they consume and lead to cascading effects that disrupt ecosystem functioning. Black rats (Rattus rattus) are a prevalent threat on tropical islands. Here, we used stable isotopes to reveal patterns in the foraging ecology of black rats (n = 43) on two tropical islands in the Abrolhos archipelago, southwestern Atlantic Ocean. Contrary to our predictions, rats from the smaller island (3 ha), with greater seabird density, relied more on terrestrial resources than rats from the larger (31 ha) island, which were highly dependent (~ 50% of diet) on seabird resources. We attribute this finding to varying levels of spatial segregation among habitats between the islands. On the smaller island, only rats sampled inside the colony had a high contribution from seabirds, while those sampled outside the colony had their foraging apparently constrained within the small patch of grassland habitat. On the larger island, however, individuals consumed seabird resources regardless of the sampling area, although the sampling locations were farer apart, suggesting lower spatial segregation. A greater foraging segregation in the smaller island could be related to a higher population density of rats, increasing competition and territoriality. Rats inside seabird colonies were larger and heavier than in grassland areas, likely by having access to marine-derived resources, suggesting these individuals could defend their prime foraging territory against others. Our results highlight the capacity of black rats to rely either on marine or terrestrial resources on tropical islands, providing population resilience for this island invader.
... In her work on New Zealand islands, Jones (2010a,b) found that seabird-derived nitrogen, measured as the stable isotope δ 15 N in soils, plants, and top predator spiders, was lowest on rat-invaded islands but had the potential to recover to never-invaded levels if rats were eradicated. Plant and invertebrate abundance and composition are fundamentally shifted when rats invade on New Zealand islands as well (Grant-Hoffman et al., 2010;Towns, 2009). In the tropics, seabird-derived nitrogen in macroalgae, turf algae, and fish is higher around islands never-invaded versus those with rats (Benkwitt et al., 2021), and fish are larger and more productive around never-invaded islands compared to invaded ones (Graham et al., 2018). ...
Seabirds are one of the most threatened bird groups on the planet, with approximately 30% at risk of extinction. The primary cause of population decline and extinction are non-native species introduced to islands, such as mammals, and which subsequently prey on seabirds or damage habitats. These “invasive species” are impacting 46% of seabird species and over 170 million individual seabirds globally. Of seabirds impacted, 66% are currently listed as globally threatened on the International Union for the Conservation of Nature (IUCN) Red List, highlighting the urgent need to remove the threat of invasive species to prevent seabird extinctions. In this chapter we discuss these impacts in detail, including a brief history of invasion processes that have led to this global problem. We also describe emerging invasive species threats and investigate how climate change will further exacerbate the impacts of invasive species on seabirds. We conclude this chapter with a discussion on the successful management and reduction of invasive species, which have resulted in substantial conservation gains for seabirds and whole island ecosystems worldwide.
New Zealand's Department of Conservation is now highly experienced in the field of invasive alien animal species eradication on islands, particularly rodent eradication. The approach which has been developed addresses eradication planning at an operational level and building capacity at an organisational level. At an operational level this is done by: planning the eradication operation to be as robust and as meticulous as possible to prevent the operation failing; avoiding failure of an operation which is frequently linked to a casual approach or a 'can't be done' attitude; recognising preconditions for eradication. These are: (i) all target animals can be put at risk by the eradication technique(s), (ii) target animals must be killed at a rate exceeding their rate of increase at all densities, (iii) immigration must be zero. Building of capacity has been achieved by: (1) strategic approach-planning island eradication programmes to maxim-ise learning opportunities and minimise the risk of failure, (2) skills development-identifying training opportunities by participating in eradication operations elsewhere, (3) team approach-maintaining a committed project team and the support of higher level management, (4) peer review-an eradication advisory group provides advice on major pest eradication operations, (5) review and debrief-effectively transferring the lessons learnt with each operation to future projects. The approach outlined has application wherever eradication of invasive alien animal species on islands is planned.
Introduced species of mammals have now been removed from many islands around New Zealand, thus providing singular opportunities for ecological restoration. If island restoration is to be attempted, the way island biota originate and the precise effects of introduced organisms must be identified. Plants introduced to the New Zealand archipelago may have transitory effects, but others may modify forest structure and disrupt succession. Goats have been the most destructive introduced herbivore on islands. Among introduced predators, cats have extirpated colonies of seabirds, and rats (depending on species) affect invertebrates, lizards, and birds. Ecological theories and concepts that may help with island restoration projects include: the keystone species concept, in which the effects of one species on others is disproportionate relative to its abundance; the "intermediate predator" hypothesis, where removal of the top introduced predator may lead to rebound effects of intermediate predators; and ecological chain reactions, where local extinction of some species can cause complicated multiple effects. Problems with restoration of islands may be encountered because of meagre data on the previous effects of pests (such as predators), use of non-seral species in revegetation projects, proliferations of indigenous or introduced species that have unforeseen community effects, and inexplicable difficulties with some translocations. A restoration case study in the continental Mercury Islands and on Cuvier Island showed success with removal of introduced mammals and demonstrates the various effects of introduced browsers, grazers, and predators. A contrasting case study is provided by oceanic Mangere Island in the Chatham Islands where 22 species of avifauna have been lost, seven as permanent extinctions. Restoration targets for some New Zealand islands can be clarified by palaeoecological studies of Maori (Polynesian) middens and natural deposits. Understanding the role of disturbance in island systems may also help clarify restoration targets. When exotic keystone species are introduced, physical disturbance may be overridden by biotic disturbance. This replacement in turn has implications for trophic structure. With high levels of biotic disturbance, continental islands may be changed from relatively species-rich bottom-up food webs to species-poor top-down trophic cascades. These possibilities can be tested with an experimental approach to restoration, although such experiments may be hard to interpret because of difficulties with replicates and controls. Ecological restoration en New Zealand islands has potential to replace damaged or lost communities, expand the ranges of relict populations, reduce the selective influence of exotic (keystone) species on indigenous species, help in understanding how the systems are formed, provide opportunities for educational and scientific investigation, and act as a testing ground for new technologies against pests.
Wetas are native to New Zealand and in evolutionary terms are insect 'dinosaurs' within the Orthoptera. Related species occur in South Africa, Australia, North America and to a lesser extent, Europe. This book brings together all known information on these groups (mostly in superfamilies Stenopelmatoidea and Gryllacridoidea) to form a compendium of existing scientific knowledge for future biological investigation and conservation. It is particularly useful for those working and researching in the areas of entomology, ecology and evolution, and contains 26 chapters by various authors in sections on: Systematics and biogeography (7 chapters); Morphology and anatomy (4 chapters); Ecology (3 chapters); Behaviour (5 chapters); Reproduction and development (2 chapters); Physiology (4 chapters); and Conservation of endangered species (1 chapter). A review of the Gryllacrididae is included, because of confusion over common names. A list of contributors and an index are also provided.
Tuatara mainly used prion burrows, though they are able to dig their own. Burrows were either simple (containing a single prion nesting chamber) or complex (containing ≥2) nesting chambers). Most burrows in the Keepers Bush plot were simple while those in Ruston Bush tended to be complex. Only 1 tuatara was found in a burrow at a time. Individual tuatara used several burrows, and several tuatara used the same burrow at different times. Most tuatara used burrows in close proximity to each other, median distance between successive burrow captures being 0.7 m in Ruston and 0.6 m in Keepers. Tuatara may defend their sole occupancy of a burrow. Some large adults showed preference for certain burrows; juveniles showed little site tenacity. Incubating fairy prions can evict tuatara from burrows. During prion breeding seasons, tuatara were found more often in burrows unoccupied by birds and burrows containing chicks than in burrows containing adult birds. Although more burrows were present in Ruston than in Keepers, similar population densities of tuatara were calculated to be in each area (Ruston: 1500/ha, Keepers: 1240/ha), attributed to there being fewer bird-occupied burrows in Keepers. -from Author
Addition of nutrients to an ecosystem may increase abundances of organisms at different trophic levels. Seabirds add nutrients to the islands on which they live. Our aim was to determine whether plants, invertebrates, and lizards are utilizing nutrients provided by seabirds and whether the addition of nutrients was correlated with an increase in arthropod and reptile abundance. A higher index of abundance was found for invertebrates and lizards on islands with seabirds than on islands without seabirds in the Marlborough Sounds, New Zealand. Seabird-derived nutrients were identified in the tissues of plants, invertebrates, and lizards on seabird-inhabited islands. Nutrient addition was found to increase abundance of animals from different trophic levels, but the patterns shown were not those expected from classical, top-down, theories of food web regulation.
We observed black and white-plumaged storm petrels on 27 seabird-watching trips to the outer Hauraki Gulf, New Zealand, November 2003 - June 2005. We studied their plumage characteristics, behaviour and seasonal occurrence: the birds had common plumage characteristics and sightings of them were concentrated in the outer Hauraki Gulf from October to March and further offshore in April-May. Their presence in the Hauraki Gulf coincided with summer breeding of other seabirds, in particular white-faced storm petrels (Pelagodroma marina). Their pattern of occurrence off northern New Zealand suggests the birds may be breeding in the Hauraki Gulf; the Mokohinau Islands, rid of rats (Rattus exulans) 15 years ago, is a potential breeding site In our view these black and white storm petrels do not conform to descriptions of any extant species known from New Zealand waters, and, consequently, we speculate that our observations may have been of New Zealand storm petrels (Pealeornis maoriana Mathews 1932), a species known from only three specimens collected in the 19th century.
On Korapuki Island (Mercury Islands group, northeastern New Zealand) lizard capture frequencies increased following the removal of Pacific Rats Rattus exulans in 1986 and rabbits Oryctolagus cuniculus in 1987. This increase was dominated by diurnal Shore Skinks Oligosoma smithi. Increases in Shore Skink captures were proportionally greatest where beach particle sizes exceeded 25 cm dia (50-fold in five years). In sites where particles were large the Shore Skink population became dominated by adults. These changes in Shore Skink distribution and size were found in areas unlikely to have been either directly or indirectly affected by rabbits. The changes are therefore attributable to removal of Pacific Rats which apparently had greatest effect on lizards where interstices between rocks allowed the rats access. The selective natural recovery of Shore Skink populations on Korapuki Island indicates that the effects of Pacific Rats on island lizard faunas depends not only on the presence of refuge areas, such as rocky beaches, but also on the particle sizes within them.
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