Posted by Tynan Burkhardt @TynanBurkhardt

Nocturnal transpiration is often ignored when studying the water relations of plants, with the assumption that stomata (small pores on the bottom of leaves) close at night, leading to negligible water loss. Although transpiration is far lesser at night than during the day, it can contribute a considerable component of daily water loss. For kauri, I have found nocturnal water loss to make up around 15 % of yearly canopy transpiration. However, for other species, nocturnal transpiration can contribute up to 30 % of daily water loss!

For many plants, night-time is a period of replenishment, where the stem water storage is refilled, after being depleted during the day. However, the importance of night time in the refilling process differs between species. In South American rain forests, where water is readily available year-round, water storage is small and very little refilling occurs at night, with most occurring in the evening. In comparison, kauri have extensive water stores, which are held within their iconic large stems and branches. Refilling of these stems and branches extends almost all the way to sunrise (Figure 1), demonstrating the importance of the nocturnal replenishment period for kauri.

Figure 1 – Daily pattern of withdrawal and refilling for kauri water storage, showing diurnal withdrawal followed by evening and night-time refilling.

Kauri rely heavily on night-time refilling in their water use strategy, with water storage buffering trees from the high evaporative demand and temperatures of summer. Night-time water loss limits a plant’s ability to refill water stores and increases in drought summers. For example, most nights of the 2012/13 drought summer had a considerable amount of transpiration, compared to last summer (2017/18), where most nights had very little transpiration (Figure 2). Worryingly, drought is expected to increase in frequency and severity for many regions where kauri is present.

Figure 2 – Frequency of nights at different levels of nocturnal transpiration (E_n) for kauri canopies in a ‘normal’ summer (2017/18) and a drought summer (2012/13).

But what does this mean for kauri if drought does become a common summer condition? Clearly, they will be less able to refill their water stores, perhaps leading to a water deficit as the drought progresses. However, water storage is not the only defense kauri have against drying soils. They have also been observed to drop leaves in drier summers and close their stomata when under even mild water stress. Therefore, the reduced ability to refill water storage does not necessarily mean there will be large scale kauri die offs when drought does occur, but it is one of the pathways in which kauri stands may become more water stressed.

Tynan is a Masters student at the University of Auckland’s Ecology Ngatahi lab group. He is studying Nocturnal Transpiration in kauri trees and is supervised by Cate Macinnis-Ng.
email: tbur187@aucklanduni.ac.nz

Posted by Darren Ward @nzhymenoptera

There is increasing concern about the decline of pollinators worldwide. However, despite reports that pollinator declines are widespread, data are scarce and often geographically and taxonomically biased. These biases limit conclusions about any potential pollinator crisis.

Natural history museums have the potential to transform the field of global change biology. However, museum specimens are underused and could be better utilised to reveal patterns that are not observable from other data sources. Specimens historically collected and preserved in museums provide information on where, and when, species were collected, but also contain other ecological information such as species interactions and morphological traits.

In a recent paper we provide a global synthesis of how researchers have used historical data to identify long-term changes in pollination services. We show that scientific information on the status and trends of most pollinators is poor, if not absent. For example, although a wide variety of countries have recent records of pollinators, they lack historical data. Thus, greater emphasis should be placed on the digitisation of specimens already held in natural history museums.

Furthermore, changes in pollinator communities are context specific, and ‘global trends’ need to be assessed with caution, especially when most of the globe is not assessed!

In Spain, a hot-spot for bee diversity, data analyses showed there were a reduced number of bee species, however, this trend was highly site-specific. Declines in species were clustered around certain types of bees, such as the ground-nesting bees (especially Andrenidae), suggesting a pattern of winners and losers, where some groups of bees are more sensitive to disturbance than other groups.

In New Zealand there are relatively few native bee species, however, they are well studied, and therefore museum records can be used to identify trends in pollinator communities. In contrast to Spain, we found that 11 out of 27 bee species increased in relative occurrence over time, 13 species were stable, and only three bee species declined in relative occurrence.

A greater number of long-term datasets from different countries are needed in order to provide a robust and truly global assessment of trends in pollinator communities. Natural history museums play a central role in assessing the extent of the global pollination crisis, because they are the source which can serve as a baseline.

Bartomeus I, Stavert JR, Ward D, Aguado, O. 2019. Historic collections as a tool for assessing the global pollination crisis. Philosophical Transactions of the Royal Society B. 374, issue 1763.

From a themed issue, ‘Biological collections for understanding biodiversity in the Anthropocene’. http://rstb.royalsocietypublishing.org/content/374/1763

New Zealand bee collection records were gathered from multiple sources, including university, research institute, museum and private collections. Collection records from the New Zealand Arthropod Collection (NZAC) and are freely available online (https://scd.landcareresearch.co.nz/).

Darren Ward is an entomologist, Head Curator at the New Zealand Arthropod Collection at Landcare Research, and a senior lecturer at the School of Biological Sciences, University of Auckland.

Posted by Ellen Hume

Imagine a clear winding stream flowing from the hills above into a small yet pristine lake. Birdlife is abundant, and the water is teeming with fish including freshwater eels known as native tuna, while macrophytes, aquatic plants, provide habitat and food to the aquatic species. Over time, as people move into the area, the surrounding lush native forest makes way for paddocks of farmland. The local whānau use the waterways for gathering mahinga kai to feed their families and enjoy being connected to the beauty of nature. Eventually the landscape is one of commercial productivity, with a mosaic of cropping and grassland feeding livestock and only small pockets of fenced forest remaining. It is harder to catch fish and tuna but children still splash around in the water in warmer months. Agriculture in the area continues to intensify with further use of fertiliser and irrigation water and more animals on the land. Then one summer the stream dries down to a trickle. The lake is murky and native fish are far and few between. Aquatic plants along the once clear stream and lake beds have been replaced by masses of slimy green growth. No-one goes near the water anymore. The connection with the land, the balance, the kaitiakitanga have been lost.

So what has happened here?

Well, the situation can be explained by the concept of tipping points. A tipping point is the point at which a system changes from one state to another, sometimes quite unexpectedly. In this case, the previously healthy pristine waterway system has reached a tipping point, collapsing into a degraded unhealthy state. This is due to the gradual accumulation of small changes to the local landscape and greater human inputs increasing the nutrient levels in the water to a critical point where a significant change to the whole aquatic community occurs. This process is called eutrophication and can be very difficult to reverse due to the system being stable and resistant to change. In today’s world of change, if we could identify which systems are likely to experience tipping points then we could use management actions and policy to avoid these occurring. Knowledge of how tipping points affect a system is also invaluable when trying to shift a system purposely into another state, for example restoration of the degraded waterway and modified landscape.

Image credit: Troy Baisden

In the case of the waterway system described above, the local community rallied together to take action in claiming back their kaitiakitanga. It is a long journey but through concerted effort and connection to the land they have a strong vision to tip the system back into the healthy, functioning waterway it once was.

Ellen Hume is a PhD student funded by Te Pūnaha Matatini Centre of Research Excellence. Her project is looking at detecting temporal and spatial regime shifts to enable better risk-based decision making, with supervision from Dr Cate Macinnis-Ng and Professor Troy Baisden.

By Kaavya Benjamin @kaavyabenjamin95

Globalisation has ensured the prompt arrival of our Amazon purchases, direct flights to Hawaii and ability to share the best of what NZ has to offer with the world. However, the increase in global trade and transport has also intensified the establishment and spread of exotic insect species. These are insect species who invade areas they aren’t native. A recent study also showed that these hitchhiking invaders aren’t planning on stopping any time soon.

Exotic insect invaders can do a lot of harm to native ecosystems. For example, in NZ Vespula wasp invaders have been known to reduce honeydew by 70% and compete with the endangered Kaka. Argentine ants are one of the most problematic invaders of the insect world. Like Genghis Khan’s hordes, the abundance and aggressive nature of this species cause major problems for native birds, lizards and insects. These issues have driven numerous studies to understand the negative impacts of these invaders on native ecosystems. However, very little is known about the dynamics of their spread once established. 

More than 1,400 exotic insect species have established in NZ, that we know of. Of these over 500 are herbivores who attack numerous plant species. However, other than a few well-known examples, comparatively, there aren’t many instances of exotic insect herbivores spreading into native NZ ecosystems. This is thought to be due to the resistance of the native ecosystems to invaders because of phylogenetic differences between NZ and overseas plants.

However, the more alarming fact is that exotic insect species in NZ have not yet reached equilibrium, meaning their spread will likely continue in the future. A study in 2012 showed the vulnerability of habitats to invasion was dependent upon rates of spread of exotic species. Thus, taxonomic collections, which house specimens collected over a wide range of time and space, could help identify key drivers of population dynamics for the spread of exotic insects. This could point to management options to control/limit widespread invasion. Taxonomic collections can also come in handy when informing conservation managers where control efforts can best be targeted. I am using the New Zealand Arthropod Collection to assess the spread of herbivorous insects into native NZ ecosystems as a part of my Masters’ project. This could help DOC and MPI come up with better pest risk-assessments and provide information for invasive species research.  

Understanding the dynamics and patterns of past invaders could also result in better-informed predictions for future exotic invasions. While taxonomic collections are far from perfect, they are still a robust source of information which can aid conservation management.

Kaavya is a Masters student in the School of Biological Sciences, University of Auckland. Her project aims to assess spread, over time, of all exotic herbivorous insects into native New Zealand ecosystems. She is supervised by Darren Ward.

Posted by Yen Yi Loo @looyenyi 

How do you survive by being small? The soundscape in a New Zealand bush is filled with splendour. But among the powerful song and majestic plumage, there is a niche for all things small and sweet. In Boundary Stream Mainland Island, a forest reserve in the Hawkes Bay region, a group of tiny birds constantly flick and flutter in the trees; Tomtits, Grey warblers, Silvereyes, Robins…and the smallest of them all is the Rifleman. They are so small that a wing flap of a butterfly could be mistaken as a Rifleman. Not only that. They are also very difficult to hear. Rumour has it that people after about 50 years of age can’t hear them. And because of that, many don’t notice them among the Tūī, Bellbirds, and Kākā. I spent the first week of my PhD fieldwork tuning in to the high pitch calls of the Rifleman, tilting my head this way and that, like an owl, to pick up subtle wisps of conversation between foraging pairs. After some practice, I could finally tease apart the calls between Rifleman, Grey warblers and Tomtits, by their small differences in pitch and length.

Spotting a rifleman takes a little patience and a good sense of auditory localization,
and also ways to watch from different perspectives!
© Ines Moran

I am a first year PhD student looking at the vocal learning abilities of the Rifleman. Could they be learners? Well, we know that they are not songbirds, because they don’t sing to defend their territory or to attract mates – or do they…? But findings in the past decade have also plucked them from the suboscine group and placed them as a link between the passerines and the parrots. So here we are, trying to decipher their potential hidden skill of vocal learning. The more I spend time with them, the more I learn about their interesting behaviours. For instance, they constantly open and close their wings while hopping on branches and trunks of trees in an incredible speed of about 0.05 seconds for each ‘flick’, maybe to maintain balance due to their short of tail? And I saw a male hover for one second in the air!

“Whoa, didn’t see that branch there!”
© Yen Yi Loo

I can relate to the Rifleman in many ways. For one, I am small, even for Asian standards. For another, I speak softly – well, because I wouldn’t want to disturb the birds! And most relatable of all, I can’t sit still. Although the Rifleman don’t migrate or have large territories, they are busy little birds constantly communicating and working on staying alive. It is difficult to follow them because they move so quickly. I, too, am constantly moving; I travel the world from one side to the other, chasing little birds and learning their behaviour and language. Truth be told, there is a lot to learn wherever we go. And it led me here to this beautiful land of unique bird life. Being surrounded by the soundscape of this forest and the wonderful team that I’m working with, I am glad this is where I will spend all the summers of my PhD doing fieldwork!

The Cain Lab on the first week at Boundary Stream Mainland Island.
From left, Me: cold and numb from the NZ spring rain,
Daria Erastova: looking to expand her incredible bird list,
Sarah Withers: the pioneer of Rifleman research in the North Island,
Ines Moran: my PhD team mate – the best I could ask for,
and Kristal Cain herself!

Yen Yi Loo is a PhD student in the School of Biological Sciences, University of Auckland. Her study aims to determine whether the rifleman (Acanthisitta chloris) are vocal learners by investigating the ontogeny and temporal changes in their vocal parameters, and its implication on the evolutionary origins of vocal learning in the avian phylogenetic tree. She is supervised by Kristal Cain and Margaret Stanley.

Posted by Zach Carter

Landscape connectivity (also known as ecological connectivity or landscape permeability) is the degree to which a landscape facilitates or impedes wildlife movement. Understanding landscape connectivity has become a major conservation priority for ecological managers because it can be used to protect and restore important ecological processes; such examples include: the promotion of gene flow/dispersal, creation of risk assessments to characterise the likelihood of invasive species dispersal, and quantification of habitat fragmentation throughout peri-urban regions.

An example of landscape connectivity in practice: a conservation corridor that traverses the Trans-Canada Highway in Banff National Park to facilitate large mammal movement (image: https://conservationcorridor.org/2012/10/banff-national-park/)

Most commonly, spatially explicit connectivity models use resistance surfaces to represent landscape features. This is a graph-theoretic technique that reflects movement, represented as a pixel value in a grid within a geographic information system. Connectivity models ultimately use resistance surfaces to calculate the ecological cost associated with movement through a landscape between two termini (starting/ending points). It is assumed that the organism of interest will travel in such a way so as to minimise incurred costs. Accurate representation of these movements can then be used to make informed management decisions based on desired outcomes.

Two common models used for calculating ecological distance include the cost distance and current flow methodologies. These methods propose antithetic assumptions regarding the organism(s) emigration trajectory, where the cost distance model assumes the organism has perfect knowledge of the landscape and will, therefore, choose a path that minimises cumulative ecological costs, and the current flow model which treats the landscape as an electrical circuit and assumes the organism has no prior knowledge of the landscape whatsoever. Often these methods cannot elucidate an organism’s true understanding of the landscape and, as such, are used in conjunction to create a more complete picture.

An example cost distance (fig. A, least-cost path) and current flow (fig. B, probabilistic movement) output for a generalised mammalian disperser as it emigrates from the New Zealand mainland to an offshore island in Fiordland. The red coloured least-cost path (fig. A) represents the path of least resistance as the organism emigrates. The dark coloured areas (fig. B) represent areas of probabilistic movement from an emigrating organism (source: Z Carter).

Current flow has gained much attention recently for use in connectivity modelling because it considers probabilistic movement across all possible paths within a landscape. If maximising connectivity is the desired ecological outcome (e.g. reducing habitat fragmentation), then calculating current flow between two termini within a landscape is a good model to follow (see fig. B above). On the other hand, if the desired ecological outcome is to reduce organism dispersal (e.g. prevent the spread of invasive species) calculating the least-cost path between termini may be a good modelling option because it often overestimates connectivity. In this instance it would be better to overestimate connectivity than to under estimate it in order to produce informative ecological recommendations regarding the potential spread of a pest species.

For more reading I recommend the following publications:

Etherington, T. R. (2015). “Geographical isolation and invasion ecology.” Progress in Physical Geography 39(6): 697-710.

McRae, B. H. and P. Beier (2007). “Circuit theory predicts gene flow in plant and animal populations.” Proceedings of the National Academy of Sciences 104(50): 19885-19890.

Wade, A. A., et al. (2015). “Resistance-surface-based wildlife conservation connectivity modeling: Summary of efforts in the United States and guide for practitioners.” Gen. Tech. Rep. RMRS-GTR-333. Fort Collins, CO: US Department of Agriculture, Forest Service, Rocky Mountain Research Station. 93 p. 333.

Zach Carter is PhD candidate in the School of Biological Sciences at the University of Auckland. His research focuses on developing prioritisation models to assist eradication efforts for the Predator Free 2050 Programme. He is supervised by James Russell and George Perry.

Posted by Hester Williams @HesterW123

The rise in biological invasion, strongly related to increasing international trade and travel, is creating global ecological and economical challenges.

The process by which biological invasions occur can be divided into three phases: arrival, establishment, and spread. Early intervention in the form of detection and eradication can be one of the most cost-efficient approaches. Eradication is the deliberate elimination of an invading species from an area, and is greatly assisted by prompt detection when the newly established population is still small and not widely spread.

Given the perceived difficulty of eliminating all individuals of a species, the practicality of eradication has often been questioned. However, recent population studies indicate that low density populations of a variety of species are governed by Allee effects and this may facilitate eradication. Allee effects may arise from a variety of mechanisms (e.g. mate-location failure, failure to overcome host defences, failure to satiate predators) and create a population threshold, below which population growth rate is negative. Consequently, eradication may not require directly eliminating all individuals in a population; instead, it may only be necessary to reduce the population below the Allee threshold, and extinction will proceed without further intervention.

The loss of habitat and fragmentation, which are detrimental to rare and endangered species, are complementary in attempts to eradicate an invasive species from an area. Although habitat loss is not a cause of an Allee effect, it can reduce population size such that the population could then become succeptible to an Allee effect. Fragmentation of an invasive species population (through management actions such as host removal /fragmentation) could result in reduced patch-to-patch dispersal as well as reducing the population densities in each fragmented patch to below the Allee threshold. Thus, sufficiently small and distant patches could lead to extinction of the population.

My studies use Neolema ogloblini, a biocontrol agent for Tradescantia fluminensis, as proxy for an invasive insect pest species (Fig 1).

Fig 1: The leaf beetle, Neolema ogloblini, a biocontrol agent for Tradescantia fluminensis, with typical adult damage.

Experiments completed last summer have indicated that at small population sizes, establishment of this beetle is moderated by an Allee effect. This summer I will test the effectiveness of host removal as a management tool to achieve eradication by exploiting the Allee effect. I will remove a selected number of host patches within a meta-population of Neolema ogloblini, thereby fragmenting the remaining population and in turn subjecting it to Allee effects to achieve eradication (Fig 2).

Fig 2: Host removal as management tool to achieve eradication through exploitation of the Allee effect. A selected number of host patches within a meta-population of Neolema ogloblini will be removed (denoted by white patches), fragmenting the remaining population and in turn subjecting it to Allee effects to achieve eradication.

Results of this experiment will ultimately give guidance on what eradication approaches are more or less promising for particular invasive species.

Hester Williams is a PhD candidate in the School of Biological Sciences, University of Auckland and is stationed with the Landcare Research Biocontrol team in Lincoln, Canterbury. She is interested in invasion processes of both insect and plant species. Hester is supervised by Darren Ward (Landcare Research/University of Auckland) and Eckehard Brockerhoff (Scion), with Mandy Barron (Landcare Research) as an advisor. Her studies are supported by a joint Ministry for Primary Industries – University of Auckland scholarship. The project is an integral part of an MBIE program “A Toolkit for the Urban Battlefield” led by Scion.

Posted by James Russell @IsldJames

The answer is self-evident: because we didn’t kill all the rats. However, the answer to the question “why didn’t we kill all the rats” is more complex. Tropical rat eradications currently fail more often than those in temperate or polar regions (16.1% vs 6.3%). If we discount operational reasons (i.e. the eradication wasn’t undertaken properly), the two prevailing biological hypotheses are that either with rats constantly breeding some pups may be able to survive and re-populate the island, or food is so abundant that not all adult rats diet switch to the poison bait.

A radio-collared rat on Reiono Island (Photo: James Russell)

Experimental rat eradications have proven very profitable in the past for advancing the science of rat eradications, but not everyone wants to allow their rat eradication for conservation to be an experiment, particularly when this increases the risk of failure. This week a team of scientists from University of Auckland (Araceli Samaniego, Markus Gronwald, James Russell) have been undertaking an experiment in association with a tropical rat eradication on Reiono Island in French Polynesia. The 22 hectare island will be treated with poison to eradicate the rats which are widespread across the otherwise relatively pristine island dominated by Pisonia forest and native seabirds and reptiles.

An alive 5 day old rat pup (Photo: James Russell)

The team have radio-collared over 60 female rats and will track them throughout the course of the eradication. They will monitor their nests to determine the likelihood of any baby rats surviving over the two weeks of the eradication. This intensive monitoring effort will reveal the most detailed data yet on the behaviour of rats during a tropical eradication campaign, and hopefully inform future rat eradications on tropical islands so that they may be as successful as those undertaken in temperate and polar regions around the world.

For more information see the special issue of Biological Conservation on tropical rat eradication.