Endemic Species of Christmas Island, Indian Ocean D.J
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RECORDS OF THE WESTERN AUSTRALIAN MUSEUM 34 055–114 (2019) DOI: 10.18195/issn.0312-3162.34(2).2019.055-114 Endemic species of Christmas Island, Indian Ocean D.J. James1, P.T. Green2, W.F. Humphreys3,4 and J.C.Z. Woinarski5 1 73 Pozieres Ave, Milperra, New South Wales 2214, Australia. 2 Department of Ecology, Environment and Evolution, La Trobe University, Melbourne, Victoria 3083, Australia. 3 Western Australian Museum, Locked Bag 49, Welshpool DC, Western Australia 6986, Australia. 4 School of Biological Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia. 5 NESP Threatened Species Recovery Hub, Charles Darwin University, Casuarina, Northern Territory 0909, Australia, Corresponding author: [email protected] 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 frst 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 superfcially; 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 diffcult 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. KEYWORDS: conservation, endemism, extinction, fungi, invertebrates, island, lichen, plants, vertebrates 56 D.J. JAMES, P.T. GREEN, W.F. HUMPHREYS AND J.C.Z. WOINARSKI INTRODUCTION of proposed developments must be considered through Oceanic islands support a disproportionately large legislated environmental impact assessment processes; share of the world’s biodiversity relative to their total recognised threats to them are the subject of management area (Kier et al. 2009; Tershy et al. 2015). However, investment and control; and they are explicitly considered island-endemic species also make up a disproportionate in spatial land-use planning exercises (Butz 2004; Hill share of the world’s modern extinctions, including the 2004a; Hill 2004b; Schulz 2004; Schulz and Lumsden majority of recent extinctions in many taxonomic groups 2004; Cogger 2006). In contrast, species that may (Blackburn et al. 2004; Brooke et al. 2007; Sax and be equally imperilled but are not formally listed as Gaines, 2008; Loehle and Eschenbach, 2012; Tershy threatened are often neglected, compounding a lack et al. 2015; Doherty et al. 2016; McCreless et al. 2016; of knowledge that will constrain their likelihood of Woinarski et al. 2018). Hence, oceanic islands are a being listed as threatened and perpetuating a lack of global priority for conservation attention. conservation attention. Conservation management for any island is likely to We aim to provide an inventory of species endemic be most effective and appropriately directed if it rests to Christmas Island, as a basis for more comprehensive upon a robust knowledge base of the island’s biodiversity consideration of its biodiversity conservation values and attributes, such as the number and identity of its needs. Such an inventory is of interest and importance endemic species; and that its most imperilled species are for several reasons. First, and unusually, a substantial recognised as such. Where such information is lacking (albeit not exhaustive) inventory of the plants and or limited, there may be a high risk of species declining animals of the island was compiled at about the time or going extinct before managers are aware of the of the island’s initial settlement, from the late 1880s species or aware of the need for remedial management (Boulenger 1887, 1889; Butler 1887, 1889; Dendy 1887; action (Régnier et al. 2009; Régnier et al. 2015a; Régnier Pocock 1887, 1900; Sharpe 1887, 1900; Thomas 1887, et al. 2015b). Such risks may be particularly severe for 1889; Waterhouse 1887; Gahan 1889; Lister 1889; Smith endemic species that are relatively inconspicuous and 1889; Ridley 1891, 1906a,b; Waterhouse et al. 1900). uncharismatic and those in relatively poorly-known Part of the explicit purpose of this early collection work taxonomic groups, such as most invertebrates (Diniz- was to provide an exemplary baseline against which Filho et al. 2010; Diniz-Filho et al. 2013): in contrast, changes in the island’s biota (due to settlement and human island birds and mammals are generally well-known and influence) could subsequently be assessed (Andrews the focus of most conservation attention. 1900c; Andrews 1909): ‘It has not hitherto been possible to watch carefully the immediate effects produced by 2 Here we consider the biodiversity of the 137 km the immigration of civilized man – and the animals and Christmas Island, an Australian external territory in plants which follow in his wake – upon the physical the tropical eastern Indian Ocean, and its conservation conditions and upon the indigenous fauna and fora of prioritisation. There is a marked taxonomic bias in the an isolated oceanic island. I hope to arrange that this global and national (Australian, under the Environment shall be done in the case of Christmas Island’ (Murray Protection and Biodiversity Conservation Act) listing 1900). To some extent, this current paper facilitates some of threatened species (Walsh et al. 2012), which is such assessment of the post-settlement fate of the island’s particularly pronounced in the case of Christmas endemic biota. Regrettably, calamity befell the next major Island. Of its 14 endemic terrestrial vertebrate species, collection, by Carl Gibson-Hill collected over a 2-year twelve are listed as threatened or extinct (Table 1), period from 1938–40: ‘the greater part of the material and a further fve endemic subspecies of terrestrial obtained, covering the majority of the insect groups, was vertebrates are also listed as threatened at the national destroyed, unidentifed, when the Kuala Lumpur Museum level. For plants, one of the island’s 16 endemic species was bombed in 1945’ (Gibson-Hill 1949b). is listed as threatened, along with one endemic variety Second, from the time of the earliest biological and two local populations of plant species with much sampling, the distinctiveness and endemicity of the more widespread distributions. In contrast, only one of island’s biota was recognised. For example, the frst Christmas Island’s c. 200 endemic invertebrate species visiting naturalist, J.J. Lister in 1887, reported that ‘the is listed as threatened globally and none are listed most striking factor is the peculiarity of the fauna’ (Lister nationally. In part, this disparity refects contrasts in the 1889). amount of knowledge available for different taxonomic groups, but it is also a consequence of a pervasive Third, the island has a highly unusual ecological tendency to highlight the conservation concerns of context, largely determined by extremely high densities more charismatic taxonomic groups at the expense of of a single invertebrate species, the red crab Gecarcoidea those with less public appeal (Cardoso et al. 2011a; natalis (O’Dowd and Lake 1991; Green 1997; Green et al. Cardoso et al. 2011b; Walsh et al. 2012). In the case 1997, 1999). of Christmas Island biodiversity, listing as threatened However, since the 1980s, the island’s ecology has under Australian legislation provides some notable been subverted through ‘invasional meltdown’ (Green conservation benefts: listed species tend to be regularly et al. 2001, 2011) due to the extensive establishment monitored, such that information on population trends of supercolonies of the invasive yellow crazy ant is routinely available; the potential impacts upon them Anoplolepis gracilipes, which have encompassed up to ENDEMIC SPECIES OF CHRISTMAS ISLAND 57 25–30% of the island at times (Abbott 2006).