Community conservation: ‘HIMBY’ not ‘NIMBY’

Posted by Margaret Stanley @mc_stanley1

I recently participated in a community conservation forum, when a community engagement colleague coined the acronym ‘HIMBY’. I was exasperated by what I perceived as the community not being able to see the ‘big picture’ of evidence-based strategy around pest management and restoration.

 “It’s the opposite of NIMBY [Not In My BackYard]” she said. “It HAS to be In My BackYard – HIMBY”. And she’s dead right. This particular scenario is increasingly raising its head as community groups voraciously compete for conservation funding and action.

Of course we desperately need highly activated communities to be engaged in conservation and restoration. We can enhance biodiversity over a larger area with limited resources when community groups and volunteers give their time and energy for free. It’s also important to have place-based conservation – this allows a sense of ownership and community buy-in that allows sustainability of people and groups over time. Ecologists have long since recognised that ecological science alone won’t solve conservation problems, and social science and community partnership is a critical cog in the conservation wheel.

However, we also need to remind our communities about the risks of ‘HIMBY’ and community-based conservation. One of the major risks of a national emphasis on community-based conservation is that funding could be diverted away from areas that don’t have people – then we could end up in a situation where much of our conservation action is not taking place on land that is representative of different ecosystem types/biodiversity. In fact, we know that community conservation is biased towards coastal forest ecosystems, where people are concentrated.

At a local level, where funding and resources are prioritised and allocated within regions or cities, ‘HIMBY’ is alive and well. Community groups within cities/regions are understandably vying for resources. However, prioritisation of pest management must incorporate more than community activation. Firstly, it must be cost-effective and have preventative outcomes, rather than the ambulance at the bottom of the cliff. We should prioritise prevention. The Treasure Islands programme which funds pathway biosecurity to prevent pest invasion on Hauraki Gulf Islands both 1) protects assets with previous large investment in removing pests (e.g. Rangitoto-Motutapu Islands) and 2) prevents new invasions, thereby saving money in the long term. We know how cost-effective it is in medicine to vaccinate rather than belatedly treat the disease.

Given the impacts of Aotearoa-New Zealand’s invasion debt, we have to continue to ‘treat the disease’ and reduce pests and restore habitat. But the ‘where’ should be decided strategically. Yes, the degree to which a community is activated is a key factor in prioritisation along with other cultural and societal factors, but ecological factors (beyond our backyards), such as level of pest infestation, the value of the conservation assets within sites, and habitat connectivity, should be key factors in deciding where conservation actions should take place to achieve the best outcomes for biodiversity across the city or region.

Invasion Curve Animation  – explains the principles of prioritization for pest management based on cost-effectiveness (You Tube: ‘ Invasion Curve Animation Biosecurity Council of WA’).

Although we’re primed as humans to be highly attached to ‘our backyard’ and want the best outcomes for it, we need to see the wood for the trees. This is why larger-scale conservation visions, such as the North-West Wildlink and Cape to City are becoming increasingly important. If we can all buy into the larger landscape scale conservation vision, then we will be willing to see that the priorities for action/$$ spent might not be in our backyard, but over the fence, in someone else’s backyard. We’ll also understand that by taking action in the neighbour’s backyard, we will benefit from the biodiversity spilling over into our backyard.

Time to look up from our backyards and take on the larger vision.

Dedicated to the champion work of conservation staff within agencies engaging with communities, and also to those champion activators within our communities, rallying people to conservation action!

Margaret Stanley

Dr Margaret Stanley is an Associate Professor in Ecology, School of Biological Sciences, University of Auckland. Most of her research is applied ecology, working to improve outcomes for biodiversity.

Celebrate fruit fly detections in New Zealand

Posted by Prof Jacqueline Beggs @JacquelineBeggs

About to bite into that luscious, juicy taste of summer, a tree-ripened nectarine? Be thankful you do not live anywhere with fruit fly.  This group of insects are infamous for the damage they do to a wide range of fruit and vegetables.

Apricot (left) and pear (right) are two of the many fruits affected by fruit fly. Images used by permission Plant Health Australia

As well as summerfruit, they attack citrus, apples, pears, berries, grapes, olives, persimmons, tomatoes, capsicum, eggplant, and avocado. We are not talking a bit of cosmetic damage to the skin – fruit can end up as a soft, mushy, inedible mess. Fruit fly females lay eggs into fruit and the developing maggots munch away, causing the fruit to rot and drop to the ground.

The extent of damage can be devastating. The island of Nauru ended up home to four species of pest fruit fly.  By 1998, about 95% of mango were infested and island-grown fresh fruit and vegetables were so scarce locals had to rely on more expensive imported produce. Fortunately, an intensive lure and poison programme eradicated three of the four species and mango and breadfruit were back on the menu.

Australia is not so lucky. They have two highly damaging fruit fly species, the Queensland fruit fly and Mediterranean fruit fly. Commercial growers spend hundreds of millions of dollars on various control measures and quarantine measures are in place to try to stop the spread into uninfested areas. With varying degrees of success.

A single Queensland fruit fly (Bactrocera tryoni) was recently detected in Devonport, New Zealand. A full scale response has been triggered as it is regarded as a serious pest [Image: James Niland, Wikimedia commons ].

It is no surprise then that detection of two different species of fruit fly in New Zealand in a week makes headline news and our dollar falls. Finding a second Queensland fruit fly near to the first is concerning. We certainly do not want them to establish. However, I think we should also celebrate. The detections are really New Zealand’s biosecurity system operating at its best. We have in place a world class fruit fly detection system; a nationwide surveillance network of 7737 traps baited with fruit fly specific lures that are checked seasonally.

Including the three latest finds, this network has detected 13 incursions of economically important fruit flies since 1989.  More importantly, early detection and effective control means fruit flies have not established in New Zealand. With such high stakes, it is critical that we keep going with research to improve surveillance, eradication and control tools. Recent PhD work at University of Auckland by Dr Lloyd Stringer is a good example; he developed a population model that helps to identify the most successful management and eradication options for Queensland fruit fly.

We cannot afford to take our foot off the pedal. Fruit fly will keep pushing at our border since there are around 80 pest species found in many countries we trade with and travel to. Furthermore, some regions have given up trying to achieve area wide fruit fly control, leading to higher density of these pests. That makes it easier for an individual fly to slip past all the measures we have in place to keep them out. So hats off to all the folk involved in keeping fruit fly at bay. That includes you – letting biosecurity officers onto your property to check for infestation, making sure you do not move fruit or veges from “controlled areas”, and encouraging everyone to never bring undeclared produce into New Zealand.

Prof Jacqueline Beggs is Director of the Centre for Biodiversity and Biosecurity, a member of the Biosecurity Ministerial Advisory Committee and co-supervised Dr Lloyd Stringer for his PhD research. And nectarines are probably her favourite fruit!

If a tree falls in the forest, and no one hears it…

The demise of long-term population monitoring

Posted by Margaret Stanley @mc_stanley1

“Is there any evidence that an introduced insect – other than a social insect – has caused the decline of a native species in New Zealand?”

A feeling of total frustration and helplessness came over me when I heard those words – while standing before an EPA panel deciding whether to allow a generalist insect predator into New Zealand for biocontrol of a crop pest.

The answer to this is “no”. The frustration comes from the fact that we have no evidence, because there is no long-term monitoring of native insect populations in New Zealand. The Dept. of Conservation (DoC) may have data for a few threatened species (perhaps wetapunga?), but not for common insect species – those that might follow the fate of the passenger pigeon if an additional invasive predator is the thing that tips the balance for that population. The example I gave the EPA in answer to that question was anecdotal – the decline of our native mantis as a result of the invasive South African mantis. There’s certainly no long-term population monitoring that has picked up the demise of the native mantis.

The lack of long-term monitoring for non-charismatic species (e.g. bees) has also been lamented in Europe lately, where a massive decline of insects in Germany over the last few decades has been detected by the Krefeld Entomological Society: a group of mostly amateur entomologists, recording insects since 1905. They have recorded declines of up to 80% since the early 1980s – that’s a lot of bird food (if you care only for vertebrates!).

biodviersity weather station

Plans for long-term biodiversity monitoring in Germany (Vogel 2007)

Changes in science funding over the last few decades, and the vagaries of politics, means that long-term population monitoring is no longer ‘sexy’ and not worthy of funding (‘Cinderella Science’: unloved and underpaid). These types of datasets are difficult to maintain because they exceed cycles of funding and government administration. In New Zealand we now lament the loss of amazing datasets that have provided the foundation and impetus for some amazing science around ecology, conservation and pest control: e.g. the Orongorongo Valley dataset, and the long term monitoring of wasps, pests and birds in Nelson.

beech seed

Seedfall of hinau and hard beech trees in the Orongorongo Valley 1968-1991 (Fitzgerald & Gibb 2001)

DoC and some councils do undertake regular biodiversity monitoring where they can, but on a reduced number of taxa (usually birds and vegetation), not often at a population level (except for threatened species), and the data are often held within these organisations, rather than open access sites. Some scientists also try to sneak in a long-term monitoring project where their (often unfunded) time and resources allow.

Instead, community groups in New Zealand, those groups undertaking pest control and restoring ecosystems, are taking up the slack in long-term ecological monitoring. At least for vegetation and birds, they are the ones undertaking regular and long-term monitoring via vegetation plots and bird counts. There is also the rise of citizen science – with large numbers of people recording biodiversity: counting kereru and garden birds. Although scientists are doing what they can to give community groups technical advice, and make citizen science more robust, will the data being collected be robust enough to understand how disturbance, invasion, and climate change are affecting biodiversity? Community restoration often takes place primarily where people are (close to urban centres), and restoration projects are dominated by lowland coastal forest ecosystems. Hardly representative of New Zealand’s ecosystems.

Needless to say, there was great excitement within the ecological/entomological community with the initiation of NZ’s National Science Challenges. The idea was mooted that we could have a Long Term Ecological Research network (LETR) like that funded by the National Science Foundation (NSF) in the USA. This network of sites provides the research platforms and long-term datasets necessary to document and analyse environmental change. There are numerous papers that summarise the benefits of long-term ecological datasets, such as: (1) quantifying and understanding how ecosystems respond to change; (2) understanding complex ecosystem processes that occur over long time periods; (3) providing core ecological data to develop, parameterise and validate theoretical and simulation models; (4) acting as platforms for collaborative, transdisciplinary research; and (5) providing data and understanding at scales relevant to management (Lindenmayer et al. 2012). Surely gaining an in-depth understanding of New Zealand populations and ecosystems over time would allow us to understand their resilience to the effects of long-term and large-scale drivers like climate change, and even the effects of new invasive species, such as myrtle rust?

However, it was not to be. And although citizen science and community monitoring is valuable in its own right for specific purposes, it doesn’t allow us to respond to the opening salvo.

If an insect goes extinct in the forest, will anyone know?

Postscript: The EPA decided not to allow import of the predatory insect – not so much because the ecological risk was perceived to be particularly high – but the industry benefits were seen as too low relative to the risk.


MargaretDr Margaret Stanley is a Senior Lecturer in Ecology, School of Biological Sciences, University of Auckland and is the programme director of the Masters in Biosecurity and Conservation. Her interests in terrestrial community ecology are diverse, but can be grouped into three main research strands: urban ecology; invasion ecology; and plant-animal interactions.

Growing old with caterpillars

Posted by Zane McGrath

For the remainder of these summer months I will be searching far and wide for the kawakawa plant. It isn’t the odour emitted by its heart shaped leaves or berries I am attracted to, but the caterpillars hosted by the plant, which I will attempt to adopt and take back to their new home, the luxurious lab at Landcare Research. Although in highlighting the beauty of ecological research, and just to make things more confusing (see earlier posts by Sam and Carolina on ecological complexity), it is not the plant or the caterpillars that will be the main focus of my Masters research, but parasitoid wasps which emerge from the caterpillars.


The kawakawa plant (top) and kawakawa caterpillar (bottom)


Parasitoid wasps spend part of their life cycle within a host, such as a caterpillar, and basically eat their way out when ready to pupate, eventually killing the host. Fascinating or down right freaky (have a look for yourself in this video), parasitoid wasps have the ability to act as natural enemies for controlling agricultural pests. For my Masters research I will be focusing on whether Meteorus pulchricornis, a species accidentally introduced into New Zealand, is competing with native species for caterpillar hosts.


The culprit, Meteorus pulchricornis (Photo: (top) and its cocoon hanging from a kawakawa plant, which is unique to the species (bottom)


In order to understand this, the caterpillars I collect will be reared until they reach their fate. If I’m lucky, but the caterpillar isn’t, a parasitoid wasp will emerge.

This is where I must hone my husbandry skills. The caterpillars can grow considerably over the period of a month or so before pupating. They will be fed their favourite meal, a kawakawa leaf that is replaced every five to seven days. However, as a parent would say, the growing up process isn’t always a pretty sight. Their homes can become inundated in frass (caterpillar poo), and need I say the larger the caterpillar grows, the larger the frass… but hey, it’s all part of being a parent.


Frass and a caterpillar

Zane McGrath is an MSc student in the Centre of Biodiversity and Biosecurity, School of Biological Sciences, University of Auckland. He is supervised by Darren Ward and Graham Walker (Plant and Food Research, Auckland) examining parasitism by exotic species in native environments.

Marvel takes a risk with Ant-Man whilst I assess the risk of ants

Posted by Anna Probert @AFProbert

Ant-Man. The official superhero of 2015 and my PhD

Ant-Man. The official superhero of 2015 and my PhD

I have a feeling that my beloved study group are going to be gaining quite a bit of interest this year. I would love to say that it is a result of some ground-breaking research I have conducted, but alas. The true reason why I think 2015 is The Year of the Ant, is the impending release (that’s 16th July) of Marvel Studio’s Ant-Man. For those of you that are perhaps not on my level of Marvel fandom, Ant-Man is based on the comic of the same name, where the protagonist has the ability to shrink down to the size of an insect and has superhuman strength and agility. Although in my spare time I’m still trying to discover Pym Particles, my full time role involves being a PhD student here at the UoA and looking at assessing invasive species risk to native ecosystems, using ants as a model.

Unfortunately for our native environment, when it comes to exotic species arriving and establishing in New Zealand, we often let them slide by if they don’t have a perceived potential social or economic impact. As a result, we end up with exotic plant and animal species that become naturalised in the environment. How do they affect the environments in which they naturalise? Well in most circumstances, we don’t really know.

Out in the Hunua baiting for ants. Photo credit Luke McPake

Out in the Hunua baiting for ants. Photo credit Luke McPake

Here in New Zealand we have 29 established exotic ant species (compared to only 11 native species) and very little understanding of how they are influencing the environments in which they live. The Argentine Ant is the species most people would have heard of, as it is a well-known invader worldwide, causing various negative impacts on the environments in which it invades. But what of the other 28 established exotic species we have in New Zealand? What are they doing?

I don’t have the answers… yet, but for my PhD I’m specifically going to be looking at the ways exotic ants influence the invertebrate community structure within different ecosystems, as well as investigating their role in altering ecosystem function. This will involve conducting different manipulative field trials over the upcoming spring/summer seasons – and I’m always on the lookout for field assistants, so let me know if you want to spend a day in nature out with me and the ants.

P.S. Marvel Studios, I am indeed open to sponsorship.

AnnaAnna Probert is a PhD student in the Centre for Biodiversity & Biosecurity, School of Biological Sciences, University of Auckland. She is using ants as a model to assess the risk posed by exotic invertebrates to native ecosystems. She is supervised by Margaret Stanley, Jacqueline Beggs, and Darren Ward.

How To Host A Vegetarian Invader

Posted by Jessica Devitt @Colette_Keeha

Recently I just said goodbye to roughly 200 guests. They were not thankful for the hospitality I showed them, they sometimes disliked the meals I served, so much so that they would rather starve than eat, and when I showed them to their new living quarters they would vomit on me to show their disapproval. I still really liked them though. My guests were most probably from Australia, but their descendents are all over the world. Their full name is quite a mouthful, Henosepilachna vigintioctopunctata, but we are on a first name basis now, so I go with the more common ‘hadda’ beetle.

From left:  Enjoying an early lunch of poroporo, hanging together in pyjamas, and baby-sitting

From left: Enjoying an early lunch of poroporo, hanging together in pyjamas, and baby-sitting

The hadda beetle was first discovered in Auckland, New Zealand in 2010 and is a well known pest of a large range of crop species, like potatoes and tomatoes from the Solanaceae family. As part of my MSc, I’ve host-tested the beetles on some native New Zealand Solanaceous plants, like poroporo (Solanum aviculare). Many native New Zealand plants are in decline, and native Solanaceous plants, like poroporo, are important food sources for our fruit-eating bird species. Adding more pressures, like a Solanaceae-munching hadda beetle, could push them further into decline.

To test the beetle’s host range, I did a series of experiments that could not only tell us if the beetle would eat the plants, but more importantly, if the beetle could maintain a self-sustaining population on our native plants. I used the ‘no-choice’ host-testing method, where the beetle is confined to one type of plant and the ‘multi-choice’ test, which allowed the beetles to ‘choose’ to eat or oviposit on a plant from a range choices. Early results show that hadda beetles are indeed happy to munch away and lay eggs on NZ’s native solanums. But to what effect on our plant populations? Watch this space…..

jess Jessica Devitt is a MSc student at the Centre for Biodiversity & Biosecurity, School of Biological Sciences, University of Auckland. She is researching the potential host-range of the hadda beetle in Auckland to assess how it might impact on native ecology. She is supervised by Margaret Stanley

When natives go wild: New Zealand… a global supplier of invasive species

Stringer UoA photo

Posted by Lloyd Stringer

After reading Mick Clout’s post on New Zealand’s potential as an Ark for non-native species; a source of genetically diverse species, that could be used to repopulate the historically native ranges from whence they came, I got a-thinking… Is New Zealand a source of invasive species?

In my day job I work on ways to prevent adventive species establishment in New Zealand. I was heartened to discover that Aotearoa has been exporting more than vibrant young kiwis on overseas working holidays.

As a kid I dreamed of a never ending Christmas. That has potential to come into fruition with the spread of New Zealand’s Christmas tree, the pohutukawa, Metrosideros excelsa into European countries. Meanwhile, in South Africa, pohutukawa threaten the ecologically unique Fynbos, already under threat from other invasive species, via prolific seed production leading to dense seedling stands.

A Pohutukawa in full bloom. This species typically flowers from Dec-Jan. Credit: by Ed323 at en.wikipedia (Transferred from en.wikipedia) [Public domain], from Wikimedia Common.

A Pohutukawa in full bloom. This species typically flowers from Dec-Jan. Credit: by Ed323 at en.wikipedia (Transferred from en.wikipedia) [Public domain], from Wikimedia Common.

Another successful export has been the Karaka, Corynocarpus laevigatus. This New Zealand treasure provides a risky food requiring days of preparation to detoxify the seeds prior to eating. Karaka were used in reforestation efforts in Hawaii early in 20th century where it now forms dense stands potentially shading out local, rare endemic plant species.

Possibly some of the less iconic New Zealand species making their way around the globe are the mudsnail Potamopyrgus antipodarum and flatworm Arthurdendyus triangulatus. New Zealand’s mudsnail can reach densities of up to 300,000 individuals per square metre in some rivers, modifying ecosystem processes. Whereas on land, the flatworm, predates on earthworms which could lead to secondary effects such as a reduction in soil quality and a reduction of a food source for native birds.

Perhaps what we are seeing are the New Zealand-sourced winners that could have a chance at surviving in a possible future world that is less species–rich, instead dominated by a few widespread species.

Lloyd Stringer is an invasive species entomologist at Plant & Food Research and doctoral student in the School of Biological Sciences, University of Auckland, investigating the interactions between eradication tools and Allee thresholds.

 He is supervised by Max Suckling, Jacqueline Beggs and John Kean. Here Lloyd is planning a red imported fire ant field experiment.

An ‘invasive ark’ for genetic diversity?

Posted by Mick Clout

Mick with binocularsA recent paper reveals that introduced stoats (Mustela erminea) in New Zealand have greater genetic diversity than in their native Britain, from where they were introduced in the late 1800s. The results are unusual because introducing a species to a new area is usually associated with a loss of genetic diversity, due to the small numbers released.

The current situation of stoats in Britain and New Zealand is the result of a series of ill-fated attempts at biological control of pests.

Hundreds of British stoats were introduced to New Zealand during the latter part of the 19th century (along with weasels and domestic ferrets) in a failed attempt to control rabbit numbers. Rabbits had previously been introduced to New Zealand for food and sport, but had become agricultural pests. The stoats introduced to New Zealand were ineffective at controlling rabbits, but they spread throughout much of the country and are implicated in the decline of many native birds, including kiwi and kakapo. The swimming ability of stoats has resulted in their colonization of several offshore islands, where they flourish, especially in the presence of introduced mice. Many conservation programmes now include the control or local eradication of stoats, to allow recovery of threatened endemic birds. However stoat incursions continue on some islands from which they have been eradicated. There are now plans for the complete eradication from New Zealand of these and other mammalian predators in the long term.

'Stoats have greater genetic diversity in New Zealand than in Britain, but this should not compromise attempts to control this invasive predator in NZ. Photo by Patrick Garvey.

Stoats have greater genetic diversity in New Zealand than in Britain, but this should not compromise attempts to control this invasive predator in New Zealand. Photo by Patrick Garvey.

Several decades after stoats were introduced to New Zealand, the native stoat population in Britain suffered a drastic decline in abundance when rabbits, their main prey there, were decimated by myxomatosis, which was introduced to Britain in the 1950s as a control measure for rabbits.

When the native stoat population in Britain collapsed in the wake of the introduction of myxomatosis, introduced stoats in New Zealand effectively conserved a reservoir of genetic diversity from the original British population.

Paradoxically, the misguided introduction of stoats to New Zealand has created an ‘invasive ark’ for genetic diversity of this species. However, this should not compromise efforts to control or eradicate stoats in New Zealand. Perhaps the British would like them back?

Professor Mick Clout is a vertebrate ecologist at the School of Biological Sciences, University of Auckland. Mick works on the conservation biology of threatened species, such as New Zealand’s native pigeon the kererū, as well as the ecology of invasive mammals, such as possums, hedgehogs, cats, mustelids and rodents. From 1993-2009 he chaired the IUCN Invasive Species Specialist Group (ISSG), a global group of scientific experts on invasive species.

Vespula wasps inflict widespread economic and ecological damage

Posted by Jacqueline Beggs @JacquelineBeggs


What do volcanic eruptions and invasive wasps have in common?

Mt Ruapehu erupting. Photo Craig Potton.

Mt Ruapehu erupting. Photo Craig Potton.

A recent study estimates that introduced Vespula wasps cost the New Zealand economy at least $130 million per year – equivalent to the estimated cost of the 1995-97 Ruapehu eruption.

The primary sector, particularly farming, beekeeping, horticulture and forestry bear the brunt of the economic impacts of wasps, but an already stretched health sector also shares the burden. The study did not attempt to quantify the economic impact on the tourism sector, although we know that encountering high densities of wasps puts off many people from outdoor recreation. Vespula wasps are invasive in many parts of the world, but New Zealand has the highest recorded density, not exactly our greatest claim to fame. However, I argue that the ecological impacts of wasps are far more damaging than the economic costs.

New Zealand has no native social wasps or bees, so the arrival of two species of Vespula wasp introduced a novel functional group into our ecosystems. I have spent many years studying the impact and control of wasps in South Island forests infested with endemic, honeydew-producing scale insects. Sugar-coated trees are surely a wasp’s idea of heaven. Native birds, lizards, insects and microbes all feed on honeydew, so when wasps monopolise the resource, many native species miss out. Additionally, wasps are predators of a wide range of invertebrates, attack nestling birds, and disrupt nutrient cycling.

Vespula wasps feed by trophallaxis - food gets passed around the colony making it a good target for control.

Vespula wasps feed by trophallaxis – food gets passed around the colony making it a good target for control.

Social insects are notoriously difficult to control – the social structure of colonies, high reproductive rates and dispersal ability makes management at the population level difficult. Biological control of wasps using Ichneumonid parasitoids has not been successful, although there are other potential agents such as Pneumolaelaps mites which might be more effective. Poison baiting using fipronil is very effective, but currently not commercially available. There are other options for wasp control such as pheromones or ‘RNA interference’ technology. Some of these may be developed as part of New Zealand’s Biological Heritage National Science Challenge, but don’t hold your breath for a single silver bullet arriving in time for next summer.

Unlike unpredictable, sporadic volcanic eruptions, I can reliably predict that for now there will be ongoing economic and ecological harm from Vespula wasps in those parts of the world they have invaded.

Dr Jacqueline Beggs is an Associate Professor in Ecology, School of Biological Sciences, University of Auckland.  She has failed to focus on a single topic; her research covers everything from impact and control of introduced invertebrates, to assessing the role of dung beetles and native bees in ecosystem function, and the recovery of grey faced petrels on a restoration island.

An Experimental Mouse Invasion

Posted by Helen Nathan

New research by Helen Nathan, Mick Clout, Jamie MacKay, Elaine Murphy, James Russell

IMG_3884How much damage could a couple of mice do on a pest-free island? We used a novel experimental approach to demonstrate the importance of island biosecurity.

Two house mice (one male, one female) were released onto Te Haupa (Saddle) Island, a Department of Conservation scenic reserve which had previously hosted a mouse population, but had recently been declared pest-free. For the following 8 months we returned regularly to the island to undertake live trapping, allowing us to estimate the number of individual mice on the island, and plot the growth of the invasive population over time. We also took genetic samples from captured mice to confirm descent from the two founder individuals released. After 8 months, the experiment concluded and the population was eradicated using a combination of trapping and poison.


Ear-punches were used to mark mice for identification and to provide a genetic sample

We found that population growth was initially rapid, peaking at an estimated 68 individuals 5 months after the release, then stabilising until the end of the 8 month experimental period. This pattern of growth reflects the classic model predicted by invasion biologists, but rarely observed in real-time as, in contrast to our study, the exact point in time when an invasion occurred is usually unknown. A surprise result from our genetic analysis showed that not all of the mice trapped at the end of our experiment were descended from the founding male and female. An unrelated female was first captured 3 months after the start of the invasion, and had produced offspring 1 month later. Genetic analysis suggests that this mouse most likely originated from another island off the north-east coast of New Zealand, almost certainly transported on a boat which had recently visited other nearby islands.

The extremely rapid population growth of the invading mouse population, along with the independent mouse incursion we detected, demonstrate the need for vigilant monitoring of our pest-free sanctuaries. For successful conservation and restoration of sites, invasive species populations must be detected early during colonisation to enable swift elimination, before the population becomes established.

Read the published research online now at Population Ecology

Or in the New Zealand Herald

Helen Nathan is a PhD student in the Centre for Biodiversity and Biosecurity