New Zealand, an archipelago of more than 2000 islands, has a terrestrial fauna especially depauperate in native land mammals. Kiore (Rattus exulans) was the first of four rodent species introduced by people. A project to eradicate invasive rats from Kapiti Island in 1996, represented a turning point in the technology, complexity and scale at which managers of natural heritage on New Zealand islands could operate. This paper includes case studies of some significant projects targeting rodents, sometimes with other introduced mammals, undertaken in the 12 years following Kapiti. Details of the methods, costs, results and outcomes are provided for Kapiti, Whenua Hou, Tuhua, Campbell, Raoul, Hauturu, Taukihepa, and Pomona islands, collectively representing a total of over 23,000 ha of habitat cleared of introduced mammals. Research and trials undertaken in the Kapiti project provided the basis for future environmental risk assessments, allowing other projects to focus on knowledge gaps. New trends in invasive species eradication in New Zealand include more challenging multi-species eradication projects, some of which are undertaken by self- funded community groups. To summarise the lessons of the New Zealand experience: a programmatic approach is recommended which will fit each eradication within a context or framework of goals for those islands; address biosecurity issues at the outset; build capability to attempt the most challenging and rewarding projects; facilitate investment in monitoring and manage expectations of stakeholders to ensure their ongoing support. Success breeds success but is never guaranteed.
The eradication of some introduced pests such as rats, stoats and possums in New Zealand seems increasingly feasible with successful action to date in various cities (e.g. Wellington City) and with the governments national 2050 predator-free goal. Here we specifically detail the potential benefits of urban rat eradication and find these cover a wide range of topics including a potentially reduced risk of infection from at least seven zoonotic diseases (e.g. leptospirosis, toxoplasmosis, trichinellosis, murine typhus; and three enteric diseases). Other potential benefits include: psychological benefits from increased native bird life in cities; reduced damage to food supplies; reduced rat damage to building insulation and to building walls and roofing; and reduced fires in buildings associated with rat damage. However, there is considerable uncertainty on the size of such impacts and so we outline a tentative research agenda as a first step towards quantification of the likely key public health benefits of rat eradication.
The three most invasive rat species, black or ship rat Rattus rattus, brown or Norway rats, R. norvegicus and Pacific rat, R. exulans have been incrementally introduced to islands as humans have explored the worlds oceans. They have caused serious deleterious effects through predation and competition, and extinction of many species on tropical islands, many of which are biodiversity hotspots. All three rat species are found in virtually all habitat types, including mangrove and arid shrub land. Black rats tend to dominate the literature but despite this the population biology of invasive rats, particularly Norway rats, is poorly researched on tropical islands. Pacific rats can often exceed population densities of well over 100 rats ha?1 and black rats can attain densities of 119 rats ha?1, which is much higher than recorded on most temperate islands. High densities are possibly due to high recruitment of young although the data to support this are limited. The generally
aseasonally warm climate can lead to year-round breeding but can be restricted by either density-dependent effects interacting with resource constraints often due to aridity. Apparent adverse impacts on birds have been well recorded and almost all tropical seabirds and land birds can be affected by rats. On the Pacific islands, black rats have added to declines
and extinctions of land birds caused initially by Pacific rats. Rats have likely caused unrecorded extinctions of native species on tropical islands. Further research required on invasive rats on tropical islands includes the drivers of population growth and carrying capacities that result in high densities and how these differ to temperate islands, habitat use
of rats in tropical vegetation types and interactions with other tropical species, particularly the reptiles and invertebrates, including crustaceans.
Seabirds are notoriously sensitive to introduced mammalian predators and eradication programs have benefitted seabird populations and their habitats on numerous islands throughout the world. However, less evidence is available from the tropics as to the benefits of rat eradication. Here, we report the seabird recovery and vegetation dynamics on a small coralline island of the tropical western Indian Ocean, eight years after Norway rat (Rattus norvegicus) eradication. Two species of seabirds were breeding before rat eradication (red-footed and masked boobies, Sula sula and Sula, dactylatra) and, in both species, the number of breeding pairs had an apparent increase of 22?23% per year after rat eradication. Such a high annual growth rate cannot be achieved by auto-recruitment only and our data suggest that immigration from other source populations never occurred in at least one of these species. We suggest that it is rather due to a rapid increase in breeding success, which rapidly increased the observed number of breeders since birds remained in the available-for-counting-as-breeders group for much longer. Two other species, the white tern (Gygis alba) and the brown booby (Sula leucogaster) were recorded breeding in 2014. The former species has not bred on the island since 1856 and the latter has never bred on the island. Plant cover (monospecific formation of the ruderal herb Boerhavia diffusa) dramatically increased from less than 30% of surface coverage to more than 70%. Although the initial restoration project was to eradicate all introduced mammals of the island simultaneously, house mouse (Mus musculus) eradication failed. Mouse density was high 8 years after rat eradication (32 mice/ha in dry season and 52 mice/ha in rainy season) but not higher than at a comparable tropical island of the region (Juan de Nova) where mice coexist with introduced black rats (Rattus rattus) and feral cats (Felis catus). These results are discussed in terms of the direct positive effects of rat eradication on seabirds and plants and the indirect positive effects of post-eradication seabird increase on soil manuring and vegetation recovery. Overall, our results show that on tropical islands, seabird and habitat recovery can be very rapid after rat eradication and should be implemented as a restoration tool wherever possible.
This encyclopedia illuminates a topic at the forefront of global ecology - biological invasions, or organisms that come to live in the wrong place. Written by leading scientists from around the world, the book addresses all aspects of this subject at a global level - including invasions by animals, plants, fungi, and bacteria - in succinct, alphabetically arranged articles.
Scientifically uncompromising, yet clearly written and free of jargon, the volume encompasses fields of study including biology, demography, geography, ecology, evolution, sociology, and natural history and features many cross-references, suggestions for further reading, illustrations, an appendix of the world's worst 100 invasive species, a glossary, and more.
The book features articles on well-known invasive species such the zebra mussel, chestnut blight, cheatgrass, gypsy moth, Nile perch, giant African snail, and Norway rat and details regions with especially large numbers of introduced species including the Great Lakes, Mediterranean Sea, Hawaiian Islands, Australia and New Zealand.
This work will be of great value in ecology and conservation science. Invasive species are a severe and exponentially growing problem of the environment, and one difficult even to characterize, much less contain.-Edward O. Wilson, author and scientist
"Second only to habitat loss mixed with climate disruption, invasive species represent the next most serious threat to biodiversity. The Encyclopedia of Biological Invasions, written by an impressive group of experts, now makes available to conservation biologists, managers, decision makers, and concerned citizens a comprehensive single source of this key topic."-Paul R. Ehrlich, co-author of The Dominant Animal
Between 1892 and 1930, 58 percent (30 taxa) of Hawaiian
endemic forest birds either were greatly reduced or became extinct. The order
in which the islands experienced major declines ofseveral forest birds is Oahu
(ca. 1873-1887), Hawaii (1892-1900), Mo10kai (1893-1907), Maui (18941901),
Kauai (after 1900), and Lanai (1926-1932). Loss of habitat, reduced
food supply, introduced avian diseases, as well as predation by man, feral cats,
mongooses, and Norway rats (Rattus norvegicus) all appear to have reduced
some species ofbirds, but none ofthese factors adequately explains the accelerated
rates ofdecline offorest birds that occurred after 1892.
Although it has been assumed that roofrats (Rattus rattus) reached Hawaii
with the first European ships at the end of the 18th century, there is circumstantial
evidence, independent of the bird decline data, that indicates that this
rat did not arrive until after 1840, probably between 1870 and 1880. The
hypothesis is advanced that after its establishment on Oahu in the 1870s,
R. rattus spread to the remaining large islands in the group, resulting in a
stepwise accelerated decline offorest birds on each island in turn. Hawaii thus
parallels some other Pacific islands where major reductions of birds have
followed the establishment of R. rattus. The need for precautions to prevent
rats from reaching rat-free islands in the Hawaiian group is emphasized.
Kiore were eradicated on Double Island using two different methods.
The larger islet was treated with one manual application of STORM 4 g
wax block rat baits containing 0.005% by weight Flocoumafen, in
October 1989. The smaller islet received one application of toxic
kibbled maize (0.005% bromodialone by weight) after 4 nights prefeeding
in November 1989. Kibbled maize was dispensed in silos. No
sign of kiore has since been found during four visits to both islands. The
cost per hectare for both methods were quite comparable. The nett
cost for eradication on the larger islet (19 ha) was $310/ha, the smaller
islet cost $432/ha. Both methods are considerably cheaper than the
technique used to eradicate Norway rats (R. norvegicus) from Hawea
Island. For future rodent eradication campaigns it is suggested that
aerial applications of poisons may be made on all islands greater than 50
ha, and that size should be no barrier to rodent eradication. However,
substantial non-target have been recorded when 1080 baits were
broadcast aerially to control possum. Non-target kills of a similar
magnitude may be experienced on larger and more sensitive islands.
