|Scientific Name:||Hadramphus tuberculatus|
|Species Authority:||(Pascoe, 1877)|
Karocolens tuberculatus (Pascoe, 1877)
Lyperobius tuberculatus Pascoe, 1877
Since Pascoe’s 1877 description, Hadramphus tuberculatus has been included in three genera and is synonymous with two names in the literature. Pascoe originally placed Hadramphus tuberculatus in the genus Lyperobius (Pascoe 1877), but in Kuschel’s 1971 revision the species was moved to Hadramphus Broun (Kuschel 1971). Kuschel later erected the genus Karocolens to include the type species K. pittospori (a Molytine weevil from the Poor Knights Islands, NZ) (Kuschel 1987). In 1999 however, Craw re-instated Karocolens pittospori within Hadramphus (Craw 1999) and Karocolens is now synonymised with Hadramphus.
|Red List Category & Criteria:||Critically Endangered B1ab(v)+2ab(v) ver 3.1|
This species is Critically Endangered due to its highly restricted range (EOO and AOO being less than 1km), its small population (maximum estimate of 148 with a continuing decline in the number of mature individuals) and the continued threats facing it.
Of the four Hadramphus species endemic to New Zealand, only H. tuberculatus is found on the South Island. As a consequence, the taxon faces multiple threats not experienced by its conspecifics, which are protected on off shore islands, and significant conservation challenges if extinction is to be prevented. Hadramphus tuberculatus is known only from one location and the single population has extremely low numbers (the highest weevil count was 49 beetles, in 2009). Weevil census data is extremely variable annually and it is currently uncertain if the population is stable. Genetic analysis also shows that the population has less than 1% variation in the mitochondrial CO1 gene, which is indicative of very low heterozygosity and therefore poor genetic resilience, which is important in rapidly changing environments (Fountain 2009).
Hadramphus tuberculatus is also at risk of extinction through predation, competition, disease and abiotic effects including habitat loss (by fire) and continued agricultural development on lands surrounding the Burkes Pass reserve in which it occurs. The taxon is therefore extremely susceptible to stochastic events. Despite extensive searches, the weevil is apparently absent in locations where it has been previously collected, and, the increasingly fragmented ecological landscape of Canterbury increases the need to translocate a sub-population of weevils to alternative sites as ‘insurance’ populations. This is particularly important given that the current location is adjacent to a major tourist highway with concomitant risks imposed by human activities (including fire, weeds, predators, illegal collecting and recreational activities).
Additional reasons for classifying H. tuberculatus as Critically Endangered are the necessary conservation efforts required to prevent extinction (over the next 50 years) and the global scientific value of the species. Conservation effort will need to be active and persistent over time and must include an artificial rearing program (currently very little knowledge exists for the rearing of New Zealand Molytine weevils), habitat management at the current weevil location and establishment of ‘safe haven’ reserves elsewhere in the South Canterbury landscape. These efforts will demand a long term recovery plans, resources and political will.
The scientific value of H. tuberculatus is high, particularly the biogeographic and evolutionary relationships between Hadramphus and other weevil taxa on neighbouring landmasses. New Zealand has been described as an evolutionary ‘laboratory’ in the South Pacific – an apt description that reflects the evolutionary responses to isolation, latitude, landscape and climate. Endemism within New Zealand beetle species is over 90% (Klimaszewski and Watt 1997) yet Hadramphus is an endemic genus, derived from (probably) a flightless ancestral weevil group of early Paleogene (=Tertiary) age (60 MY BP) (Craw 1999). The deep phylogenetic isolation and evolution of Hadramphus in the absence of ground dwelling mammalian predators provides opportunities for molecular clock calibration studies and rates of genetic divergence within the Curculionidae. To that extent, H. tuberculatus is distinct on a regional and global scale.
Hadramphus tuberculatus is currently known from a single location at Burkes Pass, Canterbury, South Island, New Zealand (44o 5.570’S, 170o 34.705’E). The weevil population exists in a 10.5 hectare scenic reserve (670 m above sea level) and is currently managed by the New Zealand Department of Conservation.
Sub-fossil remains of H. tuberculatus weevils (of Holocene age) suggest that the historic range of H. tuberculatus covered least 190 km between the Oxford hills in North Canterbury south to Waimate, a small town in South Canterbury (Craw 1999; Worthy and Holdaway 1996). There are two outlier records of the weevil from Nelson (northern tip of the South Island) and from Otira, on the West Coast of the South Island. However, the specimens were not confirmed by Craw’s taxonomic work (Craw 1999) and “should be regarded with some caution” (Young et al. 2008). Collection records demonstrate an altitudinal range of the weevil from sea level to 670 m asl.
Despite considerable effort to locate the weevil at historic record sites, no specimens have been found. In many cases, the host plant (Aciphylla aurea) has also been lost at these sites as agricultural activity increases. At present, Burkes Pass (a small settlement in South Canterbury) remains the single location known where Hadramphus tuberculatus survives.
|Range Map:||Click here to open the map viewer and explore range.|
The New Zealand Department of Conservation monitors the weevil population and has done so since 2004. Within the seven hectare sampling area, weevil numbers have been consistently meagre per year (average=18.5 beetles, standard error 6.32, with approximately 3 beetles /ha). The maximum estimated (Lincol-Peterson mark recapture) was 138 (from 49 located beetles).
Population estimates are complicated by sampling biases including worker effort, seasonal differences, variation in pitfall trap regime and possibly predator fluctuation -hedgehogs, rats and cats are considered the main predators of H. tuberculatus at the Burkes Pass site. Sampling H. tuberculatus is difficult and is subject to a large error (SD= 17.88055; SE=6.3217) to the extent that the population trend is uncertain at this stage.
|Habitat and Ecology:||
Hadramphus tuberculatus is apparently obligate on the herbaceous perennial Aciphylla aurea (Apiaceae), an erect spiky plant known as speargrass. Larvae are found on the thick tap roots and in soil surrounding the host plant while the adults are semi-nocturnal and feed on leaf tissues, flower stems, pollen and developing seeds. Speargrass forms part of an indigenous tussock-grassland community that includes tall tussock (Chionochloa spp.), short tussock (fescue spp.) and herbs (Celmisia spp.).
During spring (October to December), adult weevils often appear on the erect flower spikes of A. aurea, feeding on pollen and soft tissues of the flower structure. Weevil activity is crepuscular and nocturnal, the highest densities appearing on warm, humid evenings (between 10 to 20oC).
Threats to Hadramphus tuberculatus can be divided into biotic and abiotic effects. The former can be further subdivided into natural predators (bats, lizards, owls, raptors and possibly gulls) and introduced predators (rats, mice, European hedgehogs, stoats, cats and possibly birds).
The impact of indigenous predators on the weevil population is probably negligible as many of those species are in decline or in low numbers as well. However, the introduced predator guilds remain a constant threat to the small population of weevils at Burkes Pass. Like many of the Molytine weevils in New Zealand, Hadramphus tuberculatus displays a ‘drop and hide’ behaviour. Upon disturbance, the feeding weevils release themselves from the speargrass leaves and fall into the tiller base of the plant – an environment that is almost inaccessible to most predators on account of the long, closely arranged speargrass leaves that present a formidable barrier to most predators attacking from above (such as birds).
Introduced herbivores (hares, rabbits and wallabies) also have negative impact on the remaining habitat for H. tuberculatus at Burkes Pass. Problems with herbivores in the reserve include browsing of the host plant by hares, tunnelling beneath the plants by rabbits, the spread of competitive weeds, in particular lupins (Lupinus polyphyllus) by wallabies. The key effect of the herbivore threats are changes to the character of the vegetation community. However, since de-stocking of sheep, the periodic culling of wallabies and poisoning of hares, substantial improvements to the speargrass and tussock community have been observed.
The principle abiotic threat to the weevil is fire. The reserve is adjacent to State Highway 8, a busy tourist road through to the Mackenzie Basin and Southern Alps. Several fires have occurred in the reserve grasslands as a result of vehicle exhausts, however these were brought under control before spreading to the core weevil population. Lightning and electrical ignition from nearby transmission lines cannot be ruled out as possible fire sources. Open fires and camping stoves are not permitted in the reserve.
European arrival saw a very rapid, widespread and irreversible conversion of the indigenous lowland ecology into pasture and arable lands. The concomitant spread of mammalian pests probably pushed many large, flightless invertebrates into near, or complete, extinction.
The decline in numbers in recent years and the historical reduction in distribution are thought to be caused by habitat degradation, reduction in host plant numbers through fires, grazing and predation by rodents.
The Department of Conservation has a seven-step recovery plan for Hadramphus tuberculatus comprising:
1) Population studies
2) Understand weevil biology
3) Understanding weevil threats
4) Habitat restoration
5) Advocacy and community support
6) Developing artificial rearing protocols for the weevil
7) Establish populations of the weevil elsewhere in Conservancy
At present this has been successful with all items except 6 and 7. The weevil population is monitored annually using mark recapture, pitfall traps and visual searches of the speargrass plants. This work is intensive but effective (Fountain et al. 2013). Several attempts have been made to rear the weevil in captivity with some success; two larvae were reared from eggs, however pupae have died (Mike Bowie, Lincoln University, pers. comm. 2012).
Genetic analysis (DNA sequencing) indicates that some haplotypic diversity exists (in mitochondrial DNA). While this is encouraging, as heterozygosity can improve population survival during environmental change, the results of a three year PhD study completed in 2011 by Dr Emily Fountain, Lincoln University will not be available until 2015 because the researcher has embargoed the thesis. It is unclear why this is so.
Weed control requires an annual effort, while predator control (using poison and traps) has returned fewer pest catches per year, which is encouraging. Erecting a herbivore exclusion fence around the reserve would be an effective action but the community has aesthetic concerns.
Artificially rearing weevils in captivity is probably the single most effective action that will have the best chance of reducing extinction risk for the taxon. Following a successful rearing program, establishing a second population, elsewhere in the district will provide an insurance population. These two actions (rearing and translocation) should be the focus over the next 5-10 years. Currently weevil numbers are too low to safely establish a second population and doing so would increase the risk of extinction at both locations.
Establishing a second population will require careful design of a nursery enclosure, free of pests and weeds yet sufficiently natural in character for weevils to establish a viable population.
|Citation:||Chinn, W. 2014. Hadramphus tuberculatus. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 20 August 2014.|
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