Corresponding author: Benjamin D. Hoffmann ( email@example.com )
Academic editor: Darren Kriticos
© 2017 Benjamin D. Hoffmann, Russell Graham, Derek Smith.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation: Hoffmann BD, Graham R, Smith D (2017) Ant species accumulation on Lord Howe Island highlights the increasing need for effective biosecurity on islands. NeoBiota 34: 41-52. https://doi.org/10.3897/neobiota.34.10291
Islands are particularly noteworthy for global conservation because of the high number of species they host, the high levels of species endemism, and the large number and proportion of species at risk of extinction. Much of the conservation threat on islands is from invasive species. Whilst biosecurity is an increasing focus of attention for authorities globally, species are continuing to establish in new locations outside of their native ranges. Among invasive species, ants are a prominent taxon, especially on islands. Over the past decade, following the detection of one of the world’s worst invasive ant species, African big-headed ant Pheidole megacephala, the environmental management authority on world-heritage-listed Lord Howe Island has focused attention on invasive ants. This detection influenced the creation of biosecurity measures to prevent further incursions of exotic species, particularly ants. Despite these efforts, over the following decade numerous ant species were collected on the island for the first time, indicating a serious biosecurity problem. Here, we investigate the chronosequence of ant introductions to Lord Howe Island to quantify the extent and nature of the island’s ant biosecurity problem. A total of 45 species have been collected on the island and of these, 12 are considered to be endemic, and a further seven are possibly native. Nineteen of the 26 introduced species (42% of the total fauna and 73% of the introduced fauna) were only found for the first time in the last 15 years. All but two of the species that are not native to Lord Howe Island are native to the Australian mainland, indicating that the biosecurity threat comes from the transport of goods from the Australian mainland. We suggest that the pattern of accelerating ant species accumulation on Lord Howe Island is probably not an isolated phenomenon, and that it is probably occurring on most islands globally that are habitable by ants and visited by people.
alien, biological invasion, colonisation, dispersal, exotic, invasion, introduction
Islands are particularly noteworthy for global conservation efforts because they host more than 20% of the world’s terrestrial plant and vertebrate species within less than five percent of global terrestrial area (
Much of the conservation threat on islands, as well as on mainland ecosystems, arises from invasive species, which are considered to be the second largest driver of extinction globally (
Each year, more ant species are being accidentally transported by human commerce, and species already outside of their native range are further dispersing to new locations (
Lord Howe Island is located approximately 760 kilometres northeast of Sydney, Australia in the Pacific Ocean (S31.5545, E159.0841). The island is notably species rich, with a high level of endemism (
Following the detection of P. megacephala, ants became a target for biosecurity measures on Lord Howe Island to prevent further ant species introductions. Such measures included more thorough inspection of goods arriving on the island, prohibition on the importation of second-hand building materials, and strict protocols on the importation of plants and soil to the island. In addition, regular prophylactic treatments for ants commenced at the port, public awareness efforts of the issues of invasive ants were initiated, ant identification training was provided to many people. Despite these efforts, over the next decade numerous ant species were collected on the island for the first time in ad hoc ecological surveys indicating a serious biosecurity problem. Here, we investigate the chronosequence of ant introductions to Lord Howe Island to quantify the extent and nature of the island’s ant biosecurity problem.
A timeline of species discovery was generated by determining the earliest collection date of all ant species found on Lord Howe Island. These dates were identified from the labels of specimens in the ant collections of the Australian Museum in Sydney, the Australian National Insect Collection in Canberra and the Tropical Ecosystems Research Centre (TERC) in Darwin. These three collections contained the most comprehensive set of ant specimens from Lord Howe Island. They included specimens arising from both formal and informal collections by many people over the past century, commencing in 1915.
Species nomenclature follows
Information obtained from entomological collections revealed that ant species were collected for the first time on Lord Howe Island during two concerted ant biodiversity sampling events in 1915 and 2003, and six smaller-scale samplings 1966, 1979, 1995, 2000, 2005 and 2012 that were predominantly opportunistic hand collections. A total of 45 species have been collected (Table
Accumulation of ant species on Lord Howe Island. Note that species considered to be native to the island are all graphed at 1915 irrespective of when they were first found.
Species list of the ants of Lord Howe Island with date of first record and biogeographic origin. * indicates species that the authors believe may have a taxonomic issue in that these species may instead be cryptic species native to Lord Howe Island.
|Species||Year first recorded||Origin|
|Monomorium A nigrius group||1915||Possible native|
|Nylanderia sp. obscura group||1915||Possible native|
|Ochetellus glaber||1915||Possible native|
|Paraparatrechina A minutula group||1915||Possible native|
|Strumigenys perplexa||1915||Possible native|
|Technomyrmex jocosus||1915||Possible native|
|Iridomyrmex albitarsus||1966||Norfolk Island|
|Paraparatrechina sp. B||1966||exotic|
|Rhytidoponera victoriae||1966||Australian mainland|
|Stigmatomma A saundersi group||1966||endemic|
|Carebara sp.||1979||Australian mainland|
|Stigmatomma sp. B saundersi group||1979||endemic|
|Tapinoma sp. minutum group||1979||Australian mainland|
|Camponotus sp. novaehollandiae group||1995||Australian mainland|
|Doleromyrma sp.||2000||Australian mainland|
|Strumigenys xenos||2000||Australian mainland|
|Technomyrmex jocosus||2000||Australian mainland|
|Anonychomyrma sp. nitidiceps group||2003||Australian mainland|
|Crematogaster sp. queenslandica group||2003||Australian mainland|
|Iridomyrmex sp. rufoniger group||2003||Australian mainland|
|Iridomyrmex sp. vicinus group||2003||Australian mainland|
|Meronoplus minor||2003||Australian mainland|
|Monomorium sp. laeve group||2003||Australian mainland|
|Pheidole vigilans||2003||Australian mainland|
|Pheidole A pyriformis group||2003||Australian mainland|
|Pheidole sp. B pyriformis group||2003||Australian mainland|
|Pheidole sp. C pyriformis group||2003||Australian mainland|
|Tetramorium sp. striolatum group||2003||Australian mainland|
|Pheidole sp. group C||2005||Australian mainland|
|Monomorium sp. B nigrius group||2012||Australian mainland|
|Paraparatrechina sp. C minutula group||2012||Australian mainland|
|Rhytidoponera chalybaea||2012||Australian mainland|
Since humans started visiting Lord Howe Island in 1778, and subsequently colonised it in 1834 (
Since 2003, approximately coinciding with the detection of P. megacephala on Lord Howe Island, the movement of many high-risk items such as soil, plants, machinery and building materials to the island has been highly regulated. For example, plants must be soil free (except for a potting medium) and certified to be free of pests and disease, timber must be dressed, and gravel/roadbase must be certified to be Virgin Extracted Natural Material and free of pests. Additionally, there are enhanced protocols such as the prophylactic baiting at the wharf and immediate surroundings just in case ant species arrive in goods. But are these protocols preventing new ant incursions? As a demonstration that the relatively new biosecurity protocols are working, on 23 July 2016, as a result of compulsory inspection of all high-risk goods arriving on the island, ants were found for the first time arriving in cargo (Andrew Walsh and Hank Bower personal communication). Two intact colonies of mainland Australian species, Polyrhachis femorata and a Crematogaster species in the laeviceps species group, were found within timber. The cargo was rapidly quarantined and the colonies were treated with a toxic solution. Although it was clear that the biosecurity protocols worked in this instance, such protocols are unlikely to be perfect. Indeed more recently on 15 March 2017, a resident reported ants infesting a recently delivered consignment of corrugated iron. To further reduce this risk, the island’s biosecurity procedures are planned to be enhanced in the latest review of its biosecurity strategy, including compulsory inspections of all goods arriving on the island, and these inspections being conducted in a more routine way. Only with more time, potentially a decade, will it be possible to demonstrate that the biosecurity measures are preventing further ant introductions.
Even if the exact introduction date of all species found for the first time in the past two decades was known, the general pattern of recent increase in species accumulation would stand, at least up to the point of biosecurity implementation. Such an accelerating colonisation pattern of Lord Howe Island by ant species is greatly concerning. This finding begs the question, that if such species accumulation has occurred recently on such a small island associated with a mainland with a big biosecurity effort, what is happening elsewhere throughout the world where biosecurity is not such a focus? Few data are available for invertebrates globally, but very recently it has been shown that the establishment of alien insect species has nearly doubled over the last few decades in Europe (
We have a poor ability to manage or eradicate most exotic species after they establish anywhere, and this is particularly the case for ants. In the most recent global review of ant eradications, there have only been 106 successful eradications (excluding 38 that were nearing the end of their 2-year monitoring phase) from 316 attempts, and 77% of these successful eradications covered less than 5 ha (
The potential impacts that most of these species will have on people and the ecosystems on the island is unknown. Although the detrimental, and often severe, impacts of some invasive ant species are well known (
Notably, of the ant species on Lord Howe Island only five are not of Australian origin, clearly demonstrating that the biosecurity risk to the island comes primarily from the transport of goods from the Australian mainland. Indeed it is also most likely that three of the five non-Australian-mainland species, Cardiocondyla nuda, Tetramorium bicarinatum and Pheidole megacephala were accidentally transported to Lord Howe Island from the Australian mainland. Given that we are unaware of Paraparatrechina sp, B and Iridomyrmex albitarsus, being on the Australian mainland, these are possibly the only species that arrived on the island from a different source location, most likely being New Caledonia and Norfolk island respectively. Also noteworthy is the absence of other exotic ant species that are common throughout mainland Australia that have not yet been found on Lord Howe Island, including the highly invasive Argentine ant Linepithema humile. It is unclear if this absence is merely due to lack of dispersal opportunity or colonisation failure. Additionally, Lord Howe Island has not been colonised by many other highly invasive ant species that occur on islands throughout the Pacific, such as multiple fire ant species, Solenopsis spp., yellow crazy ant, Anoplolepis gracilipes, and the little fire ant Wasmannia auropunctata. It is suggested that this outcome is not due to current biosecurity protocols, but instead reflects a lack of transport pathways to Lord Howe Island from infested locations throughout the Pacific. Essentially Lord Howe Island has just been lucky.
In summary, since human settlement there has been a significant number of ant introductions to Lord Howe Island, and it appears that species accumulation on the island has accelerated in the last few of decades. It remains to be seen whether biosecurity protocols that were first implemented on the island just over a decade ago have indeed succeeded in slowing the rate of, or even completely stopping, accidental introductions. No system is perfect, and, for example, even in New Zealand and the Australian mainland where there are stringent biosecurity protocols, incursions and establishment of many taxa are a constant occurrence. If this pattern of species accumulation on Lord Howe Island really does reflect what may be happening on islands globally, then this highlights the need for biosecurity procedures on islands to be increased, especially islands of high conservation value. Even better would be to implement more effective biosecurity measures at ports of exit to prevent transport in the first place. For both strategies, this would involve greater public awareness of invasive species generally, especially ants, as well as solid understanding of how to prevent their spread, such as by preventing the unregulated movement of soil, plant materials, machinery, construction materials and other goods, enforcement of these quarantine requirements, and high biosecurity standards at ports of exit.
We thank the many people over the years that have been involved with collecting ants on Lord Howe Island. We also thank Paul Krushelnycky, Hank Bower, Dave Kelly and Mark McNeill for comments on the draft manuscript.