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Invasive rats on tropical islands: their population biology and impacts on native species

Available Online

Bunbury, Nancy

Harper, Grant. A,

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.

Eradicating Pacific rats (Rattus exulans) from Nu'utele and Nu'ulua Islands, Samoa - some of the challenges of operating in the tropcial Pacific

Available Online

Butler, D.J.

Tipamaa, F.T.

Tye, A.

Wylie, M.

The restoration of the small offshore islands of Nuutele (108ha) and Nuulua (25ha) has long been identified as a priority for biodiversity conservation in Samoa. The first step towards restoration was the aerial spreading of brodifacoum to eradicate Pacific rats (Rattus exulans) in August 2009. Procedures for the eradication followed those used in New Zealand and involved technical experts from that country. Particular challenges included a tight operational time-frame (two months), technical problems magnified by the remote location, variable reliability of weather forecasting,working with the local community, and mitigating rodenticide exposure risks for the friendly ground-dove (Gallicolumba stairi) (IUCN: vulnerable). Solutions to these challenges are discussed as guidance for similar projects in remote island locations. Follow-up monitoring between August 2009 and March 2010 indicated that the eradication had been successful, but Pacific rats were detected on Nuutele in May 2011. Nuulua has yet to be rechecked in 2011. DNA analyses are being organised to determine if these rats are survivors or re-invaders.

Comprehensive Desk-top Review of Biodiversity, Conservation and Invasive Species Information for the Kingdom of Tonga

Island and Ocean Ecosystems, BRB

Available Online

Pagad. Shyama

Situated between Fiji to the west and Samoa to the northeast, the Kingdom of Tonga (referred to as Tonga) is comprised of 171 scattered islands of which less than 50 are inhabited. The islands are mainly composed of limestone formed from uplifted coral. Current critical environmental concerns have arisen due to deforestation; damage to coral reefs and the introduction and spread of invasive alien species. Anthropogenic pressure has resulted in extensive modification of all ecosystems on the limestone islands of this group. Only uninhabited and steep volcanic islands still support large tracts of forest.

Systematics and ecology of the land crabs (Decapoda: Coenobitidae, Grapsidae and Gecarcinidae) of the Tokelau Islands, Central Pacific

Island and Ocean Ecosystems, BRB

Available Online

Wodzicki Kasimierz

Yaldwyn J.C.

The Tokelau Islands consist of three atolls (Atafu, Nukunonu and Fakaofo) approximately 500 km north of Western Samoa. Their numerous islets are formed mainly of coral sand and rubble with no standing freshwater. Sixty-one plant species have been recorded, 13 of these being introduced and 10 being adventives. There are three vegetation zones, the beach, the beach-crest, and the interior coconut/fern zone with the physiognomy of a humid tropical forest. Marine invertebrates have not been studied. One hundred and fifty insect species in 83 families have been recorded with most being widely distributed South Pacific species including several introduced agricultural pests, e.g. Rhinoceros Beetle. Some marine fishes have been listed and 7 species of lizards are known from the group. Twenty-six bird species (15 sea birds, 8 shore birds and 3 land birds) are known but none are endemic races. Domestic pigs, cats, man and the Polynesian Rat (Rattus exulans) are the only mammals. R. exulans is an economic pest as it causes considerable damage to the coconut crop and assists in the spread of filariasis.

Distribution of rat species (Rattus spp.) on the atolls of the Marshall Islands: past and present dispersal

Island and Ocean Ecosystems, BRB

Available Online

Spennemann D.H.R.

The study of dispersal processes of small mammals, and especially of rodents, has a wide range of applications and until recent years there were few publications discussing the colonisation of 'oceanic' islands by small mammals (cf. Crowell, 1986; Diamond, 1987; Hanski, 1986;Heany, 1986; Lomolino, 1986). This essay will be concerned with the distribution of rat species in the Marshall Islands and its implications on the interpretation of the settlement and human use of the atolls. It will be argued that in all instances the introduction of rats was caused by people and that accidental transport, such as rafting on drift wood and the like, is as unlikely as introduction by means of ship wrecks. Human transport as well as the rats' own inability to cross great distances of water makes them bad zoogeographical markers, as already pointed out by Braestrup (1956), but it is precisely this trait that is of concern here. This paper will argue that the Polynesian rat (Rattus exulans) was an intentional introduction to the area and that its distribution throughout the Marshall Islands was a deliberate strategy.

Atolls as settlement landscapes: Ujae, Marshall Islands

Island and Ocean Ecosystems, BRB

Available Online

Weisler Marshall I

Williamson and Sabath (1982) have demonstrated a significant relationship between modern population size and environment by examining atoll area and rainfall in the Marshall Islands. The present work seeks to extend that argument into prehistory by examining the relationship of ancient habitation sites and size of aroid pit agricultural systems to atoll land area and rainfall regime along the 1,500-3,500 mm precipitation gradient in the Marshall Islands. Four atolls were selected for study: Ebon at the wettest extent in the extreme south; Ujae and Maloelap near the center of the archipelago; and Utrok at the dry north. The first phase of this long-term archaeological program is reported. During the survey of Ujae Atoll (90 05' N, 165° 40' E), three habitation sites, an aroid pit agricultural zone, one early historic burial, and seven fish traps, weirs, and enclosures were recorded. Along with excavations at two habitation sites (8 m2 total area), 35 traditional artifacts were recovered (shell adzes, ornaments, and manufacturing tools). Seven radiocarbon age determinations document land use beginning as early as the third century A.D. A beachrock sample dated to 2450 ± 70 BP relates to atoll development. Some 4,748 bones of fish, birds, turtles, Pacific rats, lizards, humans, and possible cetaceans, along with nearly 13 kg of shellfish, provide the basis for understanding prehistoric subsistence, human adaptations to the atoll setting, and land use patterns.

Response of lizard assemblages in the Mercury Islands, New Zealand, to removal of an introduced rodent: the kiroe (Rattus exulans)

Towns, D.R.

Eradication of kiore double island, mercury group in Northern New Zealand / by Ian McFadden

McFadden, Ian

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.

The Ecology of Rattus exulans (Peale) Reviewed.

Available Online

J Morgan Williams

Several aspects of the ecology of Rattus exulans are reviewed in an effort to collate a large proportion of the widely scattered literature relating to the species. Subspecific relationships are discussed to illustrate the early confusion regarding taxonomic position. Literature convening R. exulans geographic distribution, habitat, nutrition, reproduction, movements, and competition with other species of Rattus, is reviewed and discussed.

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