Assessing the impact of introduced rats on the lizard fauna of Lord Howe Island

A project undertaken by Michael Thompson (University of Sydney) and David Chapple (Monash University)

Lord Howe Island is located 760 km northeast of Sydney. The Lord Howe Island Group (LHIG) includes the main island and 28 smaller outlying islands/islets, the most distant (23 km southeast) is the spectacular 551 m high Ball's Pyramid. The LHIG represents the eroded remnants of a previously large shield volcano that formed approximately 7 mya. The LHIG was World Heritage Listed in 1982 due to its diverse and largely endemic flora and fauna. Rats (Rattus rattus) were accidentally introduced to the island in June 1918 when the steamship ‘Makambo' ran aground and cargo was washed ashore. Rats have since been implicated in the extinction of several bird species, a species of bat, and numerous insect species. Many other species have experienced severe population declines and extirpation from the main island, and now largely persist on the surrounding islands that are rat-free.
 
The native terrestrial reptile fauna of LHI consists of two species: the LHI skink (Oligosoma lichenigerum) and the LHI gecko (Christinus guentheri). The biology and ecology of these two species is poorly known, though both are oviparous and nocturnal, with a mean body size of 80 mm snout-vent length. Previously widespread across a wide range of habitats on the main island (rainforest to grassland habitats), both species have experienced severe population declines and now largely persist on the surrounding islands where rats are absent. However, the exact distribution of each species within the LHIG is unknown as the only dedicated lizard survey was conducted in 1966, and even this survey was limited to several locations on the main island and two offshore islands. Both species are listed as Vulnerable (IUCN Red List, New South Wales, Nationally), with the two major threatening processes believed to be predation or displacement by rats and potential competition from the introduced delicate skink (Lampropholis delicata). The delicate skink was accidentally introduced to LHI in the early 1990s and has since become invasive on the island. It is extremely abundant across the entire island. The impact of the delicate skink on the two native lizard species is currently unknown.

The objectives of this project are to:

  1. determine the distribution of the LHI gecko, LHI skink and delicate skink within the Lord Howe Group of islands
  2. investigate the level of morphological and genetic differentiation in both the LHI skink and LHI gecko among islands within the Lord Howe Group of islands
  3. assess the impact of rats and the delicate skink on the two native lizard species on LHI
  4. enhance our knowledge of the biology, life-history and ecology of the three lizard species on LHI
Figure legends

Figure 1. View from Roach Island (Admiralty Islands) towards Sugarloaf Island (foreground) and Lord Howe Island. Photograph: David Chapple

Figure 2. View from Blackburn Island towards the Windy Point pitfall trapping area. Photograph: David Chapple

Figure 3. Mt Lidgbird (left) and Mt Gower (right) viewed from Blackburn Island. Photograph: David Chapple

Figure 4. North Bay viewed from Blackburn Island. Photograph: David Chapple

Figure 5. The view of the Admiralty Island from Mt Eliza. Roach Island is the largest island in the group. Photograph: David Chapple

Figure 6. Lord Howe Island gecko, Christinus guentheri. Photograph: Rebecca Bray.

Figure 7. Lord Howe Island skink, Oligosoma lichenigerum. Photograph: Rebecca Bray.

 

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