Since 1980, Christmas Island in the Indian Ocean has witnessed catastrophic declines in reptile numbers, with four of the six native reptiles currently on the verge of extinction.
It is likely that two species, the critically endangered forest skink, (Emoia nativitatis), and the native coastal skink, (Emoia atrocostata) may already be extinct, however a captive breeding program has been set up for the Lister's gecko (Lepidodactylus listeri) and blue-tailed skink (Cryptoblepharus egeriae). It's hoped that these critically-endangered species imay avoid extinction through successful reintroductions in the future. The sixth species, the endangered Christmas Island giant gecko (Cyrtodactylus sadleiri) had declined by 30% by 2008, and although reduced populations remain, it is the last remaining reptile found in the wild, with the exception of the cryptic and little known endemic blind-snake, (Ramphotyphlops exocoeti).
Taken together, this is believed to be one of the largest reptile decline problems that Australia has ever faced.
The causes of these reptile declines are unknown, but the accidental introduction of invasive species has had devastating effects on many Christmas Island animals. Park managers on Christmas Island suspect that the reptile declines have resulted from combined pressures from a range of invasive species, including cats, rats and yellow crazy ants. But two other highly invasive species: the Indian wolf snake and the giant centipede, have filled the island's vacant ecological niche of ‘small-reptile predator' with potentially devastating consequences for the endemic reptiles of Christmas Island which have no experience with such predators (introduced wolf snakes on the Indian Ocean island of Mauritius have had catastrophic impacts on the native reptiles there). However, unlike cats, rats and crazy ants, no control or eradication strategies currently exist for wolf snakes or centipedes, and management actions are yet to be implemented on Christmas Island.
It has almost become accepted that predation is the principal cause of the endemic reptile declines on Christmas Island; but this hypothesis is far from being ‘proved'. The lack of knowledge of key threats limits decision- making and management on the island, which in turn, prevents future reintroductions of the captive populations of Lister's geckos and blue- tailed skinks, currently breeding successfully both on the island and at Taronga Zoo.
Given catastrophic declines in all the other endemic reptile species on Christmas Island, we need to understand the key threats to the one reptile species that remains in the wild, the giant gecko, and the risk of further decline. This new knowledge is essential for designing management strategies to prevent further declines towards extinction.
My PhD research on Christmas Island aims to identify key threatening processes acting upon the endangered, endemic reptiles and develop ways to cost-effectively control these threats in support of future reintroductions, while mitigating the risk of further decline in the Christmas Island giant gecko.
Fieldwork will occur on Australia's offshore territory of Christmas Island from September to March in 2014 and 2015. We will use a combination of intensive mark-recapture studies during nocturnal surveys in the forest (enhanced by VHF tracking and GIS analysis) to simultaneously monitor giant geckos and invasive species. We will be seeking to analyze: species distributions, mortality, demographics, behavioural interactions and temporal / spatial overlap.
We will also examine the gut contents of invasive predators in areas where these species coexist with giant geckos, to determine if predation is occurring (we will do this using a genetic approach). We hope to then develop effective trapping methods and baits for key predators. We hope to trial these control strategies to create predator-proof exclosures for future reintroductions of captive bred species.
This PhD research project is the start of a partnership between The Australian National University - under the National Environmental Research Program's Environmental Decisions Hub (NERP's EDH) - and Parks Australia's Christmas Island National Park, a division of the Australian federal government's Department of the Environment.
Project 14259067 location - Australia, Oceania