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Special Issue Article: Tropical rat eradication. The response of black rats (Rattus rattus) to evergreen and seasonally arid habitats: Informing eradication planning on a tropical island. Biological Conservation. Volume 185, May 2015

Biodiversity Conservation, BRB

Available Online

Grant A. Harper

James C. Russell

Martijn van Dinther

Nancy Bunbury

Rat eradications on tropical islands have been less successful than operations in temperate climates. This is likely due to poor understanding of the factors unique to tropical regions that rat populations respond to, such as high numbers of land crabs, aseasonal climates and habitats not found at higher latitudes. On Aldabra Atoll, southern Seychelles, black rats were monitored for one year in three habitats over three climatic seasons to investigate changes in density and breeding to inform planning for a possible rat eradication. Rats bred all year in mangrove forest and in two of three seasons, including the dry season, in Pemphis forest, probably resulting from the saline tolerance of these habitats: lush vegetation and seeds were available there during the dry season. In contrast, rats from the adjacent mixed-scrub habitat only bred in the wet season due to desiccation of vegetation and lack of fresh water during other times of the year. Bait consumption trials showed that all rats ingested dyed bait when applied at 15 kg/ha, despite high rat densities and substantial bait interference by non-target species, but not at an application rate of 10 kg/ha. A novel bola technique was tested for distributing bait into mangrove forest, where aerially applied rat bait would normally be lost due to tidal inundation. The method is likely to improve rat exposure to bait in mangrove forest and other habitats on tropical islands, and warrants further development.

Special Issue Article: Tropical rat eradication. Invasive rat interactions and over-invasion on a coral atoll. Biological Conservation. Volume 185, May 2015

Biodiversity Conservation, BRB

Available Online

Anderson S.H

Caut. S

Lee. M.

Russell. J.C

Invasive rats are found on most island groups of the world, and usually more than one species has invaded. On tropical islands populations of different invasive rat species can co-exist on very small islands, but the population dynamics of such co-existing rat species, their impact on each other, and the mechanisms of coexistence are not well known. This lack of knowledge is a barrier to improving the success rate of tropical island rat eradications. Through an exhaustive trapping eradication campaign on a small tropical island, we study the population structure of historically established Rattus exulans where R. rattus have colonised within the last fifty years and over-invaded. We contrast this R. exulans population with a nearby island population where R. exulans exist alone. Recently invaded R. rattus numerically and morphologically dominate R. exulans; however stable isotope analyses show that the trophic position of R. exulans remains consistent regardless of the presence of R. rattus, once differences in trophic foundations of islands are accounted for. Although the trophic position of both rat species is indistinguishable, R. rattus is able to dominate R. exulans through interference competition. Our eradication attempt was interrupted by a tropical cyclone and ultimately unsuccessful, but there is some evidence that R. rattus reduced control device availability to R. exulans, which has important implications for multi-species control operations.

Special Issue Article: Tropical rat eradication. Trophic roles of black rats and seabird impacts on tropical islands: Mesopredator release or hyperpredation? Biological Conservation. Volume 185, May 2015

Biodiversity Conservation, BRB

Available Online

Le Corre. M.

Ringler. D

Russell. J.C

Rats contribute to the decline of tropical seabird populations by affecting their breeding success through direct predation of eggs and chicks. When they coexist with other predators, invasive rats may also generate indirect interactions via the changes they impose on the structure of communities and trophic interactions following invasion (hyperpredation process), or when apex predators are eradicated from the ecosystem (mesopredator release effect). Understanding these effects is necessary to implement restoration operations that actually benefit threatened seabird populations. We investigated these processes on two French tropical seabird islands of the western Indian Ocean, Europa and Juan de Nova, where black rats coexist with two different apex predator species (introduced cats and potentially native barn owls). The parallel use of several methods (diet analysis, stable isotopes, seabird monitoring) to identify trophic roles of rats revealed that the direct impact of rats on seabirds was particularly high on Europa where only rats and owls occur, with high consumption of chicks resulting in low breeding success for several seabird species. We also suggested that hyperpredation associated with top-down regulation of cats is occurring on Juan de Nova, although territoriality of cats may buffer this process. Conversely we found evidence that mesopredator release effect is unlikely, irrespective of the apex predator identity. Considering the most likely effects on both islands we provided recommendations on eradication priorities to mitigate the risk of local extinction that seabirds are currently facing.

Special Issue Article: Tropical rat eradicationFactors associated with rodent eradication failure. Biological Conservation. Volume 185, May 2015

Biodiversity Conservation, BRB

Available Online

Alifano. A

Griffiths.R

Holmes. N.D

Pott. M

Russell. J.C.

Wegmann. A.S

Will.D

Invasive rodents have an overwhelmingly detrimental impact to native flora and fauna on islands. Rodent eradications from islands have led to valuable biodiversity conservation outcomes. Tropical islands present an additional suite of challenges for rat eradications due to unique characteristics associated with these environments. To date tropical island rat eradications have failed at a higher rate than those undertaken outside the tropics. Critical knowledge gaps exist in our understanding of what drives this outcome. We collated an in-depth dataset of 216 rodenticide based rat eradication operations (33% of all known rodent eradications) in order to determine correlates of eradication failure, including both project implementation factors and target island ecology, geography and climate. We assessed both failed and successful projects, and projects inside and outside the tropics, using random forests, a statistical approach which compensates for high dimensionality within, and correlation among, predictor variables. When assessing all projects, increasing mean annual temperature, particularly above 24 °C, underscored the higher failure rate and greater difficulty of rodent eradications on islands in lower latitudes. We also found clear trends in eradication failure for factors unique to the tropics, including the presence of land crabs burrowing and hermit crabs, and coconut palms (Cocos nucifera). The presence of agriculture was also associated with failure. Aerial operations had a higher success rate than ground-based methods but success with this technique was less likely in the presence of hermit crabs and other non-target bait consumers. Factors associated with failure in ground-based eradication methods suggested limitations to project scaling such as island area and number of staff. Bait station operations were less likely to succeed when using stopping rules based on measures of rodent abundance. Factors influencing rat eradication failure in tropical environments continue to require a deeper understanding of tropical island dynamics to achieve a higher rate of eradication success.

Stop the fire ants (full video)

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SPREP

Stop little fire ants (60 sec video)

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SPREP

Stop little fire ants (30 sec video)

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SPREP

Stop little fire ants (80 sec video)

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SPREP

Learning about the Little Fire Ant = A'oa'o ma malamalama i le loi mumu la'ititi

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Secretariat of the Pacific Regional Environment Programme (SPREP)

The Little Fire Ant may be small but it has a very long scientific name - Wasmannia auropunctata. It is about 1.5 mm with a light to golden brown colour. Its home is Central and South America but it has travelled far to the Pacific islands and now lives in eight of our island countries - French Polynesia, Guam, Hawaii, New Caledonia, Papua New Guinea, Solomon Islands, Vanuatu and Wallis and Futuna.

Invasive Species Challenge Sheets / Manu ma Laau Fa'alafuá Pepa Lu'itau

Biodiversity Conservation, BRB

Available Online

Secretariat of the Pacific Regional Environment Programme (SPREP)

AIM This challenge aims to help your class learn more about invasive species in your country and how they travel across the Pacific region. CHALLENGE On an A4 or A3 sheet of paper, children can write or draw about an invasive species but their entry must portray the following: Name of the invasive species they have selected. Information about the invasive species. What country the invasive species came from originally and where it was before it came to your country. How did it come to your country? For example, by plane or by boat? Share information about where else in the Pacific islands you can find this invasive species. To help you learn more about the invasive species you could invite an expert to talk to your class on the key points above. This activity will show that your class has learnt about different invasive species, where they come from, where and how they have spread.

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