Endemic species of Christmas Island, Indian Ocean

WA Museum Records and Supplements | Updated 5 years ago

ABSTRACT – Many oceanic islands have high levels of endemism, but also high rates of extinction, such that island species constitute a markedly disproportionate share of the world’s extinctions. One important foundation for the conservation of biodiversity on islands is an inventory of endemic species. In the absence of a comprehensive inventory, conservation effort often defaults to a focus on the better-known and more conspicuous species (typically mammals and birds). Although this component of island biota often needs such conservation attention, such focus may mean that less conspicuous endemic species (especially invertebrates) are neglected and suffer high rates of loss.

In this paper, we review the available literature and online resources to compile a list of endemic species that is as comprehensive as possible for the 137 km2 oceanic Christmas Island, an Australian territory in the north-eastern Indian Ocean. This objective is helped by impressive biodiversity inventories made within a decade of the island’s first human settlement (1888) that provide a reasonable baseline from which to measure the changes associated with the island’s colonisation and development. However, there are some notable challenges in compiling this inventory: the spate of surveys that preceded and immediately followed the island’s settlement has not been matched subsequently; many groups have not been sampled, or sampled only superficially; the taxonomic fate of some of the species initially described from the island is opaque; some endemic taxa are of contested taxonomic rank; and demonstrating endemicity is difficult given that there has been relatively little sampling in the nearest lands (Java and nearby islands, about 350 km distant from Christmas Island).

We conclude that at least 253 species are endemic to Christmas Island (including 17 vascular plants, 27 molluscs, 15 crustaceans, 150 insects and 21 vertebrates). There has been a high rate of extinction of the island’s endemic mammal and reptile faunas, with at least six of the 10 endemic species now extinct or extinct in the wild. In the last decade, an endemic mammal and an endemic reptile species became extinct, and two endemic reptile species became extinct in the wild. Given the array of introduced species and other environmental disruptions now present on the island, it is highly plausible that many endemic species in less conspicuous or charismatic groups are now imperilled or already extinct; indeed, we conclude that more than 50 endemic species have not been reported for >100 years. Hence, the recognised number of extinct and of threatened species on this island is likely to be severely under-estimated. Although most of the endemic vertebrate species are listed as threatened (or extinct), only one of the c. 200 endemic invertebrate species is formally listed as threatened. This lack of listing is likely to severely understate the conservation plight of many species, and most would merit recognition as threatened.