[custom_headline type=”left” style=”margin-top: 45px;” level=”h2″ looks_like=”h5″ accent=”true”]A study of the native carabid’s diet is helping to enhance the beetle’s chances of survival in new habitats[/custom_headline]

 

For three years, Unitec’s Dr Stephane Boyer has been analysing the diet of native carabids (Megadromus guerinii) found on Christchurch’s Banks Peninsula. The science lecturer’s findings have provided essential knowledge for the restoration of Ōtamahua/Quail Island, and will aid in the understanding of native beetles, including their role in food webs and function in New Zealand native ecosystems.

Carabid beetles play an important role. The predatory insects help to contribute to soil fertility, vegetation renewal and weed control, and provide a food source for other animals. Boyer’s diet analysis, funded by the Brian Mason Trust, aimed to determine why 44 of the black flightless beetles, native to Banks Peninsula, did not survive translocation to Quail Island. After molecular analysis of the carabid’s faeces, Boyer has determined that the hypothesised lack of food on the island was most likely not responsible for the beetle’s inability to survive. “We found that the native ground beetle feeds on a wide variety of insect larvae including flies, other beetles and moths, many of which are present on Quail Island,” he says. “Therefore, reasons for the disappearance of the translocated individuals are unlikely to relate to inappropriate food.”

His study was part of an ongoing restoration project on Quail Island. The small island, inside Lyttleton Harbour on Banks Peninsula, was home to the now extinct New Zealand Quail and a number of other species, before the land was cleared by Maori and European settlers. The 85ha recreational reserve, administered by the Department of Conservation (DoC), has been the focus of restoration efforts for the past 20 years by the Ōtamahua/Quail Island Ecological Restoration Trust, in partnership with DoC and Te Hapu o Ngāti Wheke of Rāpaki.

“The main aim of the Trust was to facilitate the restoration of indigenous vegetation and fauna on Ōtamahua/Quail Island and provide refuge for locally extinct or rare and endangered species of the Banks Peninsula region,” trustee and Lincoln University ecologist Mike Bowie explained in his 2008 paper, Ecological restoration of the invertebrate fauna on Quail Island (Ōtamahua). With help from a number of volunteers, the Trust has attempted to restore the island to its pre-human state, through the replanting of over 100 species of native plants and controlling invasive predators, such as deer, possums and rats.

Although the island is now largely predator-free (apart from mice, which are difficult to eradicate), it has been hard for native species to recolonise the reserve, due to it being an island. As Boyer explains, “although the new conditions have prompted the return of a number of birds, such as bellbirds and kereru, and penguins are now nesting on the island, Quail Island remains out of reach for many other native animals that would have likely lived on the island prior to human arrival.” Bowie, Boyer’s former Lincoln University colleague, has been on the Quail Island Trust for over 15 years, and has been instrumental in reintroducing native species to the island. “On Banks Peninsula there are roughly 50 [species of] carabid beetle, whereas on Quail Island there are probably only about five,” Bowie explains. “The ones we are particularly interested in are the Banks Peninsula endemic species.”

[x_pullquote cite=”Boyer” type=”left”] “The predatory insects help to contribute to soil fertility, vegetation renewal and weed control, and provide a food source for other animals”[/x_pullquote]

The Trust reintroduced a number of these carabids, along with weta and leaf vein slugs. These were collected from Banks Peninsula and transported to Quail Island in weta motels – hollow wooden containers which the weta crawls into – and wooden discs, which carabids naturally inhabit. “These artificial shelters were also used to monitor the survival of the animals after release,” says Boyer. “Although most translocations were successful, there is one particular case where 22 male and 22 female native ground beetles were reintroduced, but none could be recovered after a year.”

Bowie enlisted Boyer’s help with this issue, knowing he was well qualified for such research, his PhD having focused on the ecology of invasive and native cockroaches on two French islands in the Indian Ocean. Much of Boyer’s other work has focused on invertebrates, and the conservation of native species.

With predators largely eradicated, Boyer thought a possible explanation for the carabids’ death was the lack of appropriate food on the island. To ascertain the exact contents of their diet, with help from students, carabids were collected from Banks Peninsula. These were placed in petri dishes lined with paper towels. The beetle’s faecal matter was then collected and analysed, and the beetles returned to their original location. Initial samples provided insufficient data, so experiments were repeated the next year. Former post-doctoral student Dr Richard Winkworth helped with the more complex sequence analysis. “This [data] was analysed using next-generation DNA sequencing methods,” explains Boyer”.

“This allowed us to identify which prey were eaten, from the DNA traces that remain in the faeces of predators after digestion.”

Boyer says he was not entirely surprised at the range found in the carabid’s diet. After discovering that the prey species of the carabid were largely available on Quail Island, diet was ruled out as an issue in their survival.

The next hypothesis is that the lack of habitat available on the island was responsible for their inability to thrive. Carabids nest under old pieces of wood or rotting tree trunks, and there are not a large number of these on the island.

While Boyer is not involved in this phase of the project, including the next attempt at translocating carabids, he plans to make recommendations relating to their habitat, such as leaving more wooden discs to rot on the island. These will mimic dead tree trunks and provide safe havens from mice, possible predators of the beetles. Boyer also recommends using the same diet analysis techniques in future restoration projects.

“The molecular protocol developed for this study is applicable to other carabid beetles and other invertebrate predators in general,” he explains. “It is advisable to conduct this sort of analysis prior to the translocation of endangered species in areas outside of their current distribution.”

contact
Dr Stephane Boyer
sboyer@unitec.ac.nz