Christmas Island National Park

Christmas Island

Christmas Island National Park

Christmas Island
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Hunter D.A.,Climate Change and Water | Hunter D.A.,University of Canberra | Smith M.J.,Christmas Island National Park | Scroggie M.P.,Arthur Rylah Institute for Environmental Research
Journal of Herpetology | Year: 2011

Over the past three decades the Booroolong Frog (Litoria booroolongensis) has declined across the majority of its range, with predation from introduced fish hypothesized as contributing to this decline. In this study we undertook an experiment in artificial enclosures to test the propensity for three introduced fish species (European Carp, Cyprinus carpio; Redfin Perch, Perca fluviatilis; and Mosquito Fish, Gambusia holbrooki) to prey on L. booroolongensis tadpoles. We manipulated the presence-absence of refuge habitat and alternative prey to examine how these two factors may affect tadpole predation risk. All three fish species consumed L. booroolongensis tadpoles, with juvenile C. carpio consuming nearly all tadpoles in all treatments. The provision of rocks within enclosures did not reduce the proportion of tadpoles consumed for any of the fish species examined; however, there was a reduction in the proportion of tadpoles consumed by P. fluviatilis and G. holbrooki when alternative prey were present. Although L. booroolongensis currently persists in streams inhabited by these introduced fish, this study supports the likelihood that these species are having a negative impact on populations of this endangered frog. © 2011 Society for the Study of Amphibians and Reptiles.

Smith M.J.,Christmas Island National Park | Cogger H.,College Street | Tiernan B.,Christmas Island National Park | Maple D.,Christmas Island National Park | And 4 more authors.
Herpetological Conservation and Biology | Year: 2012

Christmas Island in the Indian Ocean is home to a terrestrial reptile community that includes five endemic species; Lepidodactylus listeri, Cyrtodactylus sadleiri, Emoia nativitatis, Cryptoblepharus egeriae, and Ramphotyphlops exocoeti, and one native species E. atrocostata. Over the last 30 or so years, five of the six species have declined to near extinction with the remaining species, C. sadleiri, still reasonably common. A further five species are exotic introductions, the most recent being the Asian Wolf Snake (Lycodon capucinus) in the 1980s. Here, we document the declines in the native species and discuss possible causal factors in view of the available knowledge. We conclude that predation by introduced species is likely to be the key factor in the declines of the native reptiles, but other processes, such as interspecific competition, may also be important. We briefly describe the current management efforts and suggest several additional management actions that could be useful to conservation of the Island's terrestrial reptile community. © 2012. Michael J. Smith. All Rights Reserved.

Weeks A.R.,Cesar | Weeks A.R.,University of Melbourne | Smith M.J.,Christmas Island National Park | van Rooyen A.,Cesar | And 3 more authors.
Conservation Genetics | Year: 2014

The red crab, Gecarcoidea natalis, is endemic to Christmas Island in the Indian Ocean and largely responsible for shaping the unique ecosystem found throughout the island's rainforests. However, the introduction and establishment of supercolonies of the highly invasive yellow crazy ant, Anoplolepis gracilipes, has decimated red crab numbers over the last several decades. This poses a significant risk to the future conservation of G. natalis and consequently threatens the integrity of the unique island ecosystem. Here we undertook a population genetic analysis of G. natalis using a combination of 11 microsatellite markers and sequencing of the mitochondrial cytochrome oxidase subunit I gene from samples collected on Christmas Island as well as a single location from North Keeling Island (located approximately 900 km west of Christmas Island). The genetic results indicate that G. natalis is a single panmictic population on Christmas Island, with no spatial genetic structure or restricted gene flow apparent between sampled locations. Further, G. natalis from North Keeling Island are not genetically distinct and are recent immigrants from Christmas Island. The effective population size of G. natalis has likely remained large and stable on Christmas Island throughout its evolutionary history with relatively moderate to high levels of genetic diversity in microsatellite loci and mitochondrial haplotypes assessed in this study. For management purposes G. natalis can be considered a single panmictic population, which should simplify conservation efforts for the genetic management of this iconic island species. © 2014 Springer Science+Business Media Dordrecht.

Green P.T.,La Trobe University | O'Dowd D.J.,Monash University | Abbott K.L.,Monash University | Jeffery M.,Christmas Island National Park | And 2 more authors.
Ecology | Year: 2011

In multiply invaded ecosystems, introduced species should interact with each other as well as with native species. Invader-invader interactions may affect the success of further invaders by altering attributes of recipient communities and propagule pressure. The invasional meltdown hypothesis (IMH) posits that positive interactions among invaders initiate positive population-level feedback that intensifies impacts and promotes secondary invasions. IMH remains controversial: few studies show feedback between invaders that amplifies their effects, and none yet demonstrate facilitation of entry and spread of secondary invaders. Our results show that supercolonies of an alien ant, promoted by mutualism with introduced honeydew-secreting scale insects, permitted invasion by an exotic land snail on Christmas Island, Indian Ocean. Modeling of land snail spread over 750 sites across 135 km 2 over seven years showed that the probability of land snail invasion was facilitated 253-fold in ant supercolonies but impeded in intact forest where predaceous native land crabs remained abundant. Land snail occurrence at neighboring sites, a measure of propagule pressure, also promoted land snail spread. Site comparisons and experiments revealed that ant supercolonies, by killing land crabs but not land snails, disrupted biotic resistance and provided enemy-free space. Predation pressure on land snails was lower (28.6%), survival 115 times longer, and abundance 20-fold greater in supercolonies than in intact forest. Whole-ecosystem suppression of supercolonies reversed the probability of land snail invasion by allowing recolonization of land crabs; land snails were much less likely (0.79%) to invade sites where supercolonies were suppressed than where they remained intact. Our results provide strong empirical evidence for IMH by demonstrating that mutualism between invaders reconfigures key interactions in the recipient community. This facilitates entry of secondary invaders and elevates propagule pressure, propagating their spread at the whole-ecosystem level. We show that identification and management of key facilitative interactions in invaded ecosystems can be used to reverse impacts and restore resistance to further invasions. © 2011 by the Ecological Society of America.

Woinarski J.C.Z.,Charles Darwin University | Flakus S.,Christmas Island National Park | James D.J.,26 McLean Avenue | Tiernan B.,Christmas Island National Park | And 2 more authors.
Acta Chiropterologica | Year: 2014

Flying-foxes (Pteropodidae) show a high rate of island endemism, but island-endemic taxa have shown a high rate of decline and extinction, mostly because their small population sizes are susceptible to hunting pressure and habitat loss. The Christmas Island flying-fox is restricted to the 135 Km 2 Christmas Island (Indian Ocean), as either an endemic species Pteropus natalis or a markedly distinct subspecies of Pteropus melanotus. Given recent declines and extinctions of other native vertebrate species on this Island, this study sought to monitor population trends for this taxon. Monitoring flying-foxes at roost sites is difficult because they are highly vagile, not all roost sites may be known to observers, and dense vegetation at some sites may make counts inaccurate. These constraints are particularly evident on Christmas Island. In this study, we sought to establish a monitoring program complementary to roost counts, and to assess changes in reporting rate from a baseline sampling of 107 sites spaced across the Island in 2006 to a repeat sampling of those sites in 2012. Every site was visited four times, at night, over a period of 4-6 weeks in June-July of 2006 and of 2012, and observers reported whether or not they heard or saw flying-foxes around the sample site. A reporting incidence measure (varying from 0 to 4) was derived for every site. This measure showed a significant decline (of 39%) between the 2006 and 2012 sampling. The observed rate of decline suggests that this taxon is of considerable conservation concern, and merits further conservation action: indeed in 2014 its Australian conservation status was changed from not listed to Critically Endangered. The cause of the current decline is not yet known, but this study indicates that factors additional to hunting and habitat loss may affect island flying-fox species. © Museum and Institute of Zoology PAS.

Boland C.R.J.,Australian National University | Smith M.J.,Christmas Island National Park | Maple D.,Christmas Island National Park | Tiernan B.,Christmas Island National Park | Napier F.,Christmas Island National Park
Marine Ornithology | Year: 2012

Decades of phosphate mining on Christmas Island in Abbott's Booby Papasula abbotti nesting habitat has created a conservation threat to this rare endemic seabird. The status of Abbott's Boobies could be further jeopardised by other processes, such as the impact of Yellow Crazy Ants Anoplolepis gracilipes and other invasive species. Here we report on the current distribution of Abbott's Booby on Christmas Island based upon occupancy data collected during an island-wide survey in 2009. We used a combination of sightings and the characteristic vocalisations of the species to establish presence/absence within the area of each survey point. A subset of the survey points was repeatsurveyed, allowing us to estimate detection probabilities. Average detectability using our approach was 0.65 (SE 0.04). We related occupancy by Abbott's Booby to several environmental covariates using site-occupancy species distribution modelling techniques. We did not find any evidence of a significant relationship between occupancy by Abbott's Booby and distance to the nearest road or to high-density Yellow Crazy Ant colonies. However, we did find that occupancy by Abbott's Booby was significantly and positively related to both elevation and distance to the nearest disturbed area. Abbott's Booby nesting habitat is restricted to the central plateau on Christmas Island and has diminished because of major disturbances. There is evidence that the species now inhabits previously unoccupied areas but still does not re-occupy habitat that immediately surrounds areas cleared for phosphate mining several decades ago.

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