16 September 2014

A tangled story: the coevolution of lichen


I'm a sucker for multi-volume books. Whether it is GRR Martin's Game of Thrones, Robert Jordan's Wheel of Time, Tad William's Shadowmarch, Dennis McKiernan's Mithgar or JRR Tolkien's Middle-earth, I like nothing more than getting lost in the depth and sheer volume of story that these authors have created (all that history, setting, scale, and characters, all those interactions). Often these books are in the fantasy line but they can just as easily be science fiction, say David Brin's Uplift, or historical fiction, like Patrick O'Brian's brilliant Master and Commander. Friends often ask me to summarise these series, "What is the story about?". That's a tricky question because their scope defies a meaningful simplification. Most people are familiar with A Game of Thrones now. A simple description of this story (even more complex in the books than the TV series) is either too broad to be helpful (a fantasy version of the War of the Roses) or misses a lot (a bastard, who know nothing, talks to wolves and becomes a leader; a spoiled princess domesticates dragons and sits around in conquered cities; or a dwarf with father issues loses a nose and has a fairly miserable time).  The Wheel of Time series stretches to 13 large books with umpteen viewpoint characters and could be summarised as 'shepherd boy heals the world' but this only takes up a tenth of the story amid all of the braid tugging, gender politics and nonrandomness of events. O'Brian's series about the British navy in the Napoleonic wars stretches to 21 books and follows the career of Aubrey (as captain of larger and larger ships) and Maturin (ship's doctor, naturalist and spy) with little overarching story other than that of following the lives and careers of these fascinating characters. Even The Lord of the Rings, with a reasonably linear story, loses something when condenced to 'short tourist loses heirloom at volcanic destination'. Sometimes, then, stories are complicated and refuse to be simplified. Much the same happens in history and most definitely it happens in natural history, especially when we are dealing with evolution.

The lichen Usnea draps a beech tree
Evolutionary biologists are interested in the history of life, we want to recover the story of how life on Earth ended up as we see it. We use data from fossils and DNA, species distributions and unusual traits to recreate our best guess at summarising the evolutionary story. One area of evolutionary biology that I have been involved with since my PhD is that of coevolution - where we try to recover the story of interacting evolutionary lineages, such as parasites and hosts or pollinators and plants. Sometimes the story is fairly straightforward. The work that I did for my PhD and in various projects since has been with chewing louse species that live on seabird species (like petrels and albatrosses). Lice are insects that live in the feather forests of their hosts and are mostly passed from seabird parents to their offspring. The story of this interaction is reasonably simple, we have two lineages, one insect and the other bird, that codiverge together. When the birds speciate their lice will also become isolated and often cospeciate at the same time. Feather lice have been studied as a nice model of cospeciation for a couple of decades now. We can tell this story well. Sure there are a few quirks here and there but it is now a reasonably predictable story. Louse-host coevolution stories are like nature's little rom-coms. Not all coevolution stories are this simple.
Lichen and mistletoe colonise a beech.

Lichens, commonly seen growing on fences or trees, are composite individuals,  a symbiosis that results when a fungus cohabits with a green algae (or sometimes a cyanobacterium, or, even less commonly, with both an algae and a cyanobacterium). The fungus provides a safe habitat and food for the green algae who, in turn, use their photosynthesis ability to provide products for the fungus. Lichens are the result of this win-win coevolution relationship and would seem a prime candidate for coevolution. Hannah Buckley and her PhD student Arash Rafat joined forces with other Lincoln University ecology staff to recover the coevolution story of lichens which has now been published in the journal PeerJ. Arash collected lichens from around New Zealand. Much of the sampling was from southern beech forests and focused heavily on the lichens Usnea and Ramalina. Genes were analysed from the fungi and algae that made up the lichens. It turns out that when it comes to coevolution in lichens, it's complicated.

Lichen taxonomy is woefully understudied. There were many instances of samples that looked like the same species being genetically very different species, there were many instances of samples that looked like there were from different species being genetically similar. Certain strains of algae were found with lots of different fungal species. Geographical scale, how far sites were from one another, played a role - sites close to one another shared similar diversity. Sometimes. It seems that for lichens to function there only needed to be a fungus and alga paired and it didn't really matter which ones. All of these complications meant that the 'standard' method of analysing coevolution, by comparing phylogenetic trees for fungus and algae, was not going to be very useful, the trees were just too tangled. Hannah and Arash used a distance (principle coordinates) approach to analyse the data rather than a tree-building approach. Surprisingly, give all of the uncertainty of the lichen component species, there was  significant congruence between the genetic variation of the fungal and algal partners. The was particularly true at small spatial scales where fungi and algae species seem to co-disperse and co-adapt with each other. These patterns started to break down at larger scales and were different between lichen genera.
Lichen diversity.

So what is the story with lichens? Well, like a multi-volumed series, it's complicated. Focusing on some of the species provides a story of cospeciation. However, other species have no evidence of codivergence. Sometimes geographical scale is important, sometimes it is not. We can say that there is probably more codivergence occurring than we might have predicted. Overall, though, there is no simple summary, the evolutionary story of lichens are not very predicable. To know more we need to research more. Lichens are not rom-coms, they are art-house. Or a multi-volume series of books.

19 August 2014

Counting Katipo and the known unknowns


Former US Secretary of Defence Donald Rumsfeld made the following observation: "because as we know, there are known knowns; there are things that we know that we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns, the ones we don't know we don't know". Although this sounds a little torturous (and not in the washboarding sense!) it conveys a useful view of the world which is particularly relevant to ecology and evolution. When we do research we are usually in the business of moving 'unknown knowns' to 'known knowns'. In the process we sometimes discover some 'unknown unknowns' which then become 'known unknowns'.  Obviously, the big issues for science are the 'unknown unknowns', things that may impact on how we model the world which we currently do not take into account. In short, we can't fully explain a system if part of the explanation contains 'unknown unknowns'. Not torturous at all! 
Kaitorete Spit looking north to Banks Peninsula - Katipo country!


As an example, the history of the New Zealand biota was thought to be well known, that is there are 'known knowns'. A fragment of the supercontinent Gondwanaland broke away around 80 million years ago, gradually subsided until it was left with New Zealand and other islands. The present day biota was derived from this long isolation, one feature of which was the absence of terrestrial mammals (other than a handful of bat species). Some of the 'unknown knowns' were just how much land area remained above sea level by the period of maximum submergence around 23 million years ago, which lineages had survived in the New Zealand region versus those that had successfully colonised these islands and when these events had happened. A few years ago an 'unknown unknown' surfaced in the form of a mammal fossil from 16-20 million years ago. Fossils make for great 'unknown unknowns'. They are hard facts that are sitting out there in the crust waiting to be found. In this case the fossil became a new known and generated a bunch of known unknowns', such as how many other mammal lineages might have been around at that time, what happened to these mammal lineages as they were extinct when humans arrived in these shaky isles and how did they come to be in New Zealand?

Another area of ecology and evolution where we spend a lot of time thinking about unknowns both known and unknown is in population estimation and monitoring. For most species it is difficult or impossible to locate and count all members of a population.  We are left with trying to estimate how many individuals are out there. This could be a 'known unknown' if a species has been found to be present or an 'unknown unknown' if we are just surveying an area to see what is there (like in a biodiversity assessment). Having an accurate estimate of populations allows us to manage and conserve populations. 

Katipo (Latrodectus katipo) is New Zealand's representative of the widow family, a close relative of the the Australian red back. Katipo live in a fairly restricted and threatened habitat - the dunes of sandy beaches. Katipo are under multiple threats from land fragmentation from seashore developments, competition from an introduced spider species, and the introduction of exotic plants into dune areas. Counting katipo is a difficult enterprise. They are small and relatively cryptic. Although they build nests at the base of dune grasses, these can be obscured by storms. A recent method for counting has been developed using artificial cover objects (ACOs), in this case two small sheets of corrugated roof cladding, with wooden dowels placed between them, are placed in the field. The cladding becomes a warm and dry location that is ideal for katipo to live in. The ACOs can be placed in the dunes for weeks or months and local katipo may eventually move in, providing an estimate for local numbers. Using ACOs can help you to map put areas into dune areas of high and low densities as well as areas with no katipo.
Katipo in pingao nest, note the white egg sacs.

Lincoln University student Vikki Smith has used the ACOs to go a step further. Vikki was interested in the effect that the introduced marram grass (Ammophila arenaria) had on katipo populations (a 'known unknown'). Marram has replaced much of the native plant diversity around the dunes of New Zealand. A major casualty has been the pingao (Ficinia spirals) which is generally a smaller plant that forms less dense clumps compared to marram. Pingoa does not bind dunes together as much as marram, meaning that beaches are not as wide with marram in the dunes, as they are more resistant to wind and sea. Vikki wanted to see if katipo had a preference for the native species over the introduced. Vikki took her ACOs out to Kaitorete Spit, a thin strip of land separating Lake Ellesmere from the ocean. The spit has a good population of katipo and is one of the few places in New Zealand where you can find substantial pingao as well as marram. Vikki placed her ACOs in katipo areas with equal numbers beside marram and pingoa clumps. Vikki visited the ACOs over the next year recording katipo that she found there and reporting her findings in the Journal of Insect Conservation. Over the course of the year Vikki was 2-3 times more likely to find katipo under ACOs next to pingao compared to marram. This was most noticeable in summer and autumn. The inference is that katipo numbers are greater in pingoa and the they are more likely to colonise the ACOs through chance. So the preference of katipo for pingoa over marram has become a 'known known'. Although katipo were found in marram, the low density of katipo in this habitat may increase the chances of the local extinction of a population. How marram affects katipo populations is currently a 'known unknown' (long roots drying out the local habitat, reduction of local prey species densities, marram growth structure excluding many sites for nests). These 'known unknowns' provide a useful guide for future research. There may also be an unknown unknowns waiting for us to locate them, invisible for now until further research unearths it. that is the thrill of science!

12 August 2014

The Grand Bugapest Hotel

Your home and garden can be a very diverse place. Often when we talk about diversity we think of it as something 'out there' in the wild, away from urban areas. While urban environments might not be as diverse as many locations around New Zealand, they still contain a surprising amount of native and introduced flora and fauna, especially with arthropods. A couple of recent interviews on Radio NZ look at this idea.
First, Cor Vink takes us into his home to look at  what spiders species he can find. Cor is the inverebrate curator at Canterbury Museum and a former PhD student in the Ecology Department at Lincoln. He is acknowledged as the leading spider expert in New Zealand. Cor talks about the spider species he finds as well as what we know about white-tailed spiders (and their fearsome bite).

As well as finding what diversity is present in an urban environment, one can attempt to increase and attract more diversity. Rob Cruickshank, senior lectured here at Ecology, chats about the profusion of bug hotels that have turned up around Lincoln University campus. These hotels are a result of a collaboration between entomology and landscape architects. The hotels are built with materials that encourage invertebrates to colonise and will help with increasing the local populations. The ento students will monitor the hotels over the next year to see what happens.

25 July 2014

Biological Warfare! Organic Management of Pests 101

This blog post was written by postgraduate student Andrew Kirk in the course, Research Methods in Ecology (Ecol608). Andrew revisits a Lincoln University research area that looks at managing insect pests in organic crops from 2007.

 
Organic visions in Tuscany, Italy courtesy of Chavelli
on Flickr creative commons





Interested in organic agriculture? You're not alone. Many of us were drawn to agriculture somewhere along the line by visions of warm summer days, rolling hills, and pesticide-free produce. However, if it were that simple, everyone would grow crops organically. No 20th Century farmer would have ever abandoned the traditional practices for the forbidden fruit of the synthetic chemical. Alas, organic agriculture is tough and it most definitely is dirty.

While the challenges faced in an organic production system are numerous, we will focus here on the strategies available for the management of arthropod pests. A tremendous resource is available on this topic in the 2007 work of Zehnder, Gurr, Kuhne, Wade, Wratten, and Wyss. That review will serve as the foundation for my discussion.

The framework outlined by these authors is based on the idea of Integrated Pest Management (IPM). As the name indicates, this type of regime incorporates preventative measures, instead of simply relying on reactive measures such as the application of agrichemicals. Most conventional agriculture systems would fit the latter description, leaning heavily on agrichemicals to solve a problem after it has taken hold. However, most farmers are intelligent, practical people. Synthetic chemicals, pesticides in our context, are often very cheap in the short-term compared to the cost of integrating Ecosystem Services into every level of production. There is no doubt, on the other hand, that pesticide residue is everywhere in our world, even on organic produce that we would like to assume to be safe. For instance, have a quick look at the toxicity report for copper sulphate, one of the most widely applied organic pesticides. With that in mind, what steps can be taken to minimise the use of chemicals on our crops?

The first phase of organic pest management includes the cultural practices that can help regulate pest populations. Most basic among these is site selection. An interesting example here is the geographic distribution of fruit production in the United States. 65 per cent of this production can be found in Western states with an arid summer climate that is inhospitable to many of the devastating insect and fungi pests of horticulture. Anecdotally, much of the fruit grown in other highlighted areas of that map is native to its respective location and has internal mechanisms for dealing with pest problems. On a more local level, many "old-timers" in an agricultural community will often gladly impart some knowledge about the best site for a particular crop.

Isolation and rotation are also of particular importance in devising a strategy for cultural management of pests. Essentially, the idea is to disrupt the spread of a particular pest by limiting the area in which it thrives. One can achieve this by planting a diverse range of crops, or rotating them, to create a wider range of environments for a pest to deal with. One can easily see how this idea conflicts with the monoculture situation found in many developed countries. On the other hand, veering away from monoculture will increase the cost of management in many instances. Proponents of an IPM system will probably counter-argue that this investment will be returned through reduced input costs and spillover benefits. So maybe we'll keep moving!

Inter-row and under-vine cover crops are often used as a
substitute for crop rotation in Viticulture, for the purpose
of attracting beneficial insects to compete with harmful
insects. Photo by Bela Hausmann on Flickr creative
commons.
Next, we turn to the ecological engineering to initiate our second phase of pest management. At the centre of this idea is the encouragement of ecosystems that allow the natural enemies and competitors of a given pest to thrive. This practice, known as conservation bio-control, is a relatively new idea in the applied ecology field. It requires one to do more than introduce a natural enemy as a bio-control agent, but to also manipulate its surroundings to create the desired result. It's sort of like being the referee of the football match and giving one side water breaks while the other team runs laps around the field. This is somewhat of an indirect approach to ecological engineering, though.

A more direct route might be found in intercropping, which works similarly to crop rotation. The core of both strategies is to make it as difficult as possible for the pest to establish a large core population. A variation on these is what is known as trap cropping. As the name indicates, this entails the luring of a pest species to a more attractive plant than the commercial crop in question. Zehnder et al. mention a classic example in New Zealand sweetcorn production, where the southern green stink bug is cleverly lured to the black mustard plant, instead.

The southern green stink bug is exhibit A of
effective trap cropping. Apparently it is
very fond of black mustard. Photo from Marcello
Consolo on creative commons via Flickr.
As alluded to before, the introduction of bio-control agents can be an important part of an organic pest management system.There are two types of bio-control releases and it is important to understand the difference. Inundation bio-control relies upon the released organisms, themselves, to alleviate the pest situation. An inoculation bio-control release takes a long view, one where the progeny of the inoculation group are expected to provide relief from the pest well into the future. Of particular note among the bio-control agent success stories is the development of Bacillus thuringensis, a fungi that is pathogenic to many arthropod species of insects. If that seems like biological warfare, it's because it is. Nevertheless, the track record of bio-control is decidedly mixed. Biological systems are complex, after all, and trying to manipulate them can be very tricky. For that reason, most researchers do not recommend bio-control agents by themselves, but rather as part of an IPM system.


Photo by jetsandzeppelins on Flickr
creative commons
Last comes the part of organic pest management that everyone likes to forget. That, of course, is the fact that some pesticides are permitted in an organic management regime. These chemicals are required to be biological or minerally-based, a definition that can seem quite arbitrary to those on the outside looking in. Rememember our old friend foe, copper sulphate! With regard to insects, though, a number of organic insecticide and pheromone products are available, but individual countries have different laws regulating their use. One interesting case is an insecticidal agent formed by the bacterium Saccharopolyspora spinosa during fermentation. This insecticide is thought to be environmentally safe in the long run, but is only permissible in the EU when obtained directly through fermentation, as opposed to a purification process. According to Zehnder et al. Discrepancy over regulation of organic insecticides represents one of the major challenges to the international trade of organic goods.
Organic reality courtesy of Antony*** on Flickr
creative commons
In truth, the organic management of pests is a challenge that deserves a review much longer than this. However, with some key concepts emphasised, you can branch out into a more detailed study of these strategies. Perhaps the most important thing to remember is that pest management starts on day one, not the day after the rains and humidity come. By understanding the life-cycle and tendencies of the pest, a grower can (try to) stay one step ahead of the pest. While that goal sounds like hard work and means less time for the enjoyment of sunny days and rolling hills, it is probably a more accurate depiction of the organic dream.


References

Zehnder, G., Gurr, G. M., Kühne, S., Wade, M. R., Wratten, S. D., & Wyss, E. (2007). Arthropod pest management in organic crops. Annu. Rev. Entomol., 52, 57-80.

22 July 2014

Which wine to take home? Sensory analyses of wine regions provides a clue


This blog post was written by postgraduate student Yunxuan Qin in the course, Research Methods in Ecology (Ecol608). Yunxuan revisits a Lincoln University research area that looks at how the region of origin affects wine traits from 2013.

Walking through wine aisles in a supermarket, different brands of wines fill the shelves. Besides all the appealing labels, there must be some inherent differences hidden within the bottles. Unless opened and tasted, the characteristics of the wine remain a secret. However, there is always a clue on the label, indicating where the grapevines were planted and the wine region of origin. Indeed, the expression of regionality is an important part of the philosophy of winemakers in all parts of the world.

Wine shelves in a French supermarket. Photo by christine592, CC BY-ND 2.0. 
That philosophy about regionality is based on a concept, "terroir", which has long been recognized but is difficult to interpret. Terroir itself includes many factors, such as climate, soil type, and topography. The common understanding of terroir is "a sense of place" that wines from specific geographic locations can be perceived as different. According to Patrick Iland's, past Senior Lecturer at The University of Adelaide, book The Grapevine: from the science to the practice of growing vines for wine, terroir modifies the flavor shape of wines from different sites within a region, sub-region and even within a vineyard block. Sometimes, the soil characteristics became the predominant factor impacting on vine growth, berry composition and wine style and quality, as indicated in the figure below.
A "vine to wine" web showing vine, berry and wine characteristics from terra rossa and deep black cracking clay soils. Adopted from The Grapevine: from the science to the practice of growing vines for wine, page 287. 
If we knew the differences in wine characteristics between regions, we could easily make the purchase decision by personal wine tasting preferences, instead of standing in front of wine shelves making a hopeful selection.

Another question is how to measure wine characteristics between regions? Wine characteristics are measured by sensory attributes, which are difficult to measure. Indeed, everything related to human sensation is hard to interpret. Variables such as personal odor threshold, physiological status (with perceived astringency by saliva as an example), psychological status (with emotional attributes and wine perception as an example) and descriptive vocabulary are examples. Thus, these variables are the reason why human perception of wines will vary from person to person, which makes it difficult and impossible to establish a standardized wine tasting note for every individual wine.

A recent study from Elizabeth Tomasino and co-workers aimed at measuring the differences in Pinot noir wine according to their sensory attributes (e.g. aroma, in-mouth flavor, mouthfeel) from four regions in New Zealand. Pinot noir, one of the noblest red grape varieties, is now the most widely planted red grape variety in New Zealand with these wines frequently compared to those from Burgundy. Several degrees of latitude were covered, including Central Otago, Marlborough, Martinborough, and Waipara. These regions were studied as Pinot noir is a locally important wine variety in these places.

How did they determine wine characteristics according to different regions? Elizabeth and co-workers did a preliminary tasting by six panelists who afterwards, listed wine aroma and palate descriptors for each of the wines. Combined with previous sensory work, a final list came out, including twenty-five attributes (fifteen for aroma, four for in-mouth flavor, six for mouth-feel). The formal tasting then conducted by asking twenty-one panelists to rank the intensity of each of the twenty-five attribute.

As customers, which Pinot noir wine shall we choose from the four regions? According to the results from Elizabeth and co-workers, you can have following options. If you want something red and fruity, you'd better choose Marlborough Pinot noir wine. It was characterized by greater raspberry and red cherry aromas, a red fruit in-mouth flavor, and longer finish length with a more harmonious balance. If you prefer a note of dark fruits and oak, Martinborough Pinot noir wine should be your first choice. Greater black cherry, oak, and spice aromas and oak tannin mouthfeel describe this wine. If you desire a herbal note in your "glass of wine", then the Waipara Pinot noir will be recommended for greater barnyard with violet aromas and a decent in-mouth fruit density/concentration. If you want something neutral, choosing Central Otago Pinot noir wine would be wise. It was the intermediate one and had fuller body.

The sensory table, filled with many of the aromas wine may possess.
Photo by H. C., CC BY-NC 2.0CC BY-NC 2.0
Based on the knowledge of wine characteristics upon corresponding regions and your own preference, followed by checking the region on the label, it won't be hard to make a decision. Indeed, you already establish an expectation before opening the bottle. Another choice is doing a blind selection, and having fun to discovery the secret hidden in the bottle.

Nevertheless, nature plays a magical role on wine sensory profiles/styles according to different regions. We often address "terroir" to roughly explain the cause, but which factor of the terrior contributes the most to the differentiation remains to be discovered by scientists. Actually, one of my colleague is currently working on it (check the wine research topics in Lincoln University).

How reliable is Elizabeth research results? You have to find out by yourself. Enjoy your wine. Cheers!

Reference
Elizabeth Tomasino, Roland Harrison, Richard Sedcole, and Andy Frost,(2013) Regional differentiation of New Zealand Pinot noir wine by wine professionals using canonical variate analysis. American Journal of Enology and Viticulture.64, 357–363.

Iland, P. and Promotions, P.I.W., (2011) The grapevine: from the science to the practice of growing vines for wine. Patrick Iland Wine Promotions.



21 July 2014

The Lord of the Rings: how dendrochronology leads to a better understanding of climate dynamics


This blog post was written by postgraduate student Stefan Unterrader as part of the course, Research Methods in Ecology (Ecol608). Stefan revisits a Lincoln University research area that looks at historical climate data taken from tree rings in 2010.

Previously... on the global climate change show - It is well understood that we are facing ongoing warming of our planet's climate. Whether or not we are responsible for this process (and we are), rising temperatures around the globe have been observed for at least the last couple of decades. Although our behaviour is recognized today as a significant influencing factor for Earth's climate, it is not the only driver for today's changing climate. To get a grip on these drivers scientists often use little helpers, such as tree rings, that carry astounding potential for this task. Richard Duncan, a former professor at Lincoln University, and Pavla Fenwick, a former Lincoln PhD student, are among those scientists who are hot on the scent of such internal climate drivers using tree-ring dates from a native New Zealand tree, the pink pine. Their team of dendrochronologists - scientists who date tree-rings - pursue a promising lead which links internal climate variation to regional temperature patterns and try to explain phenomena that do not match the general global warming trend.

Residents of the Arctic Circle are concerned about rising
temperatures (Photo by Payton Chung). Tree rings can help
to better understand who's behind global warming and
how to mitigate its consequences.

Climate Change in a nutshell: Greenhouse gas concentrations were on the rise throughout the 20th century and global temperature mainly followed this worrying trend. But the devil is in the details: local and even regional temperature patterns around the globe had the cheek to behave differently. And as if this isn't enough, some cooling periods in the northern hemisphere have coincided with some rapid increases of temperature in New Zealand during the same period  (for instance, from 1940-1975). So what’s behind all this? Have New Zealanders been polluting the air to such an extent that they generate their own little hot spot? Well, chances are that humankind isn't alone being in the driver's seat to this mess. 
 


Climate proxy: extracting tree rings
 from a slice of wood (Norway spruce) and
plotting its biological growth-curve.
(Figure from the author's thesis.)

Back to the Future: In general, global climate is known to be driven by both natural and anthropogenic external forcing as well as by internal dynamics. In order to get a glimpse of Earth's climatic behaviour climatologists can use what are known as climate proxies: preserved physical characteristics of the Earth's past and present climate. Such proxy data allow for a reconstruction of climatic conditions from periods where no instrumental or historical records are available. Tree-rings can be used as such proxies because some trees, such as conifers growing in a temperate climate, will build up one tree-ring each year to grow in both size and rigidity. Based on adequate temperatures and moisture the duration of each growing season will determine the widths of tree rings: high temperatures will generally allow for wider tree-rings, and vice versa. And since many NZ tree species are climatically sensitive enough to temperature for this to be seen in their tree ring widths, we can use their tree-ring sequences as a substitution for instrumental climate records. This is actually quite useful as instrumental coverage here in New Zealand only goes back to about 1850. 

The hunt for understanding internal climate variability: Because of its isolated location and exposure to considerably high mountain ranges, New Zealand's climate is highly sensitive to variations in atmospheric circulation, the movement of air and thermal energy across the globe. With its native forests that contain many long-lived tree species, NZ is the perfect dendrochronology-lab for investigating changes in such climate circulation patterns. In their 2010 study, Duncan and his colleagues established a tree-ring chronology (a timeline based on a great number of connected, dated tree-ring samples) for Halocarpus biformis, a tree species endemic to NZ and commonly known as pink pine. Duncan's team was able to gather samples whose tree-rings were strongly influenced by temperature and significantly corresponded to instrumental temperature data in NZ. Based on this chronology they could reconstruct the mean annual temperature in NZ since the 14th century. Apart from verifying NZ's instrumental records the authors also observed several departures from a global trend of rising temperatures. On top of that, the behaviour of NZ temperatures is not in line with northern hemisphere temperatures. In fact, they appear to be sometimes directly out of phase with those in the northern hemisphere.
 
Who's in charge? Differences in climate patterns between the northern and southern hemispheres have typically been explained by the spatial variation of "radiative forcing": the effects of solar radiation, volcanoes and aerosols on Earth's climate, which all vary both in space and time. In contrast to such a global forcing, scientists identified phases when the southern hemisphere began to warm more rapidly while parts of the northern hemisphere experienced cooling temperatures. Since previous studies already identified regional climate drivers as strongly influencing large-scale temperature variations across the globe, Richard Duncan and his team took a closer look on the main modes of such internal variation: the Interdecal Pacific Oscillation (IPO) and the Atlantic Multidecadal Oscillation (AMO) which can both be derived by measuring the sea surface temperature.
 

Pink pines on Waharoa Saddle, Arthur's Pass National Park,
New Zealand (Photo kindly provided by Chris Morse).
One Pine to rule them all:  Through comparing the variations in the Pacific and Atlantic Oscillation patterns with their pink pine tree-ring chronology, Duncan and his colleagues were able to link New Zealand's temperatures to these internal oscillations for the past 550 years. At the same time they identified time intervals where NZ temperatures follow northern hemisphere temperatures and therefore a global warming trend more closely. To make a long story short, these opposing climate states (in-phase or out-of-phase with global warming) recur on a more or less regular basis and can hardly be explained by us polluting the air alone. While our influence on Earth's climate is beyond doubt, this study reinforces previous research where natural climate variation on a more regional scale still plays a powerful role in controlling New Zealand's temperatures! The story of this NZ pink pine chronology not only shows how valuable tree-rings can be for reconstructing past temperatures but also reminds us that the term "global warming" may only tell parts of the story.  


...to be continued: The study by Duncan and his colleagues is not the last piece of work in this area. The University of Auckland's dendrochronology-lab, for example, is primarily investigating kauri trees and has built up kauri tree-ring records for the last several thousand years. Tree-ring records stretching over such long time scales have been related to El Niño/Southern Oscillation  (ENSO) activity which is another key climate driver for New Zealand and likely to be more dominant in the decades to come. A current overview of what has already been done with tree-rings and other climate proxies on the southern hemisphere was given by Neukom and Gergis shortly after the release of the pink pine study. And there's definitely more to come - I wouldn't wonder if tree rings will stay a key indicator for understanding New Zealand's past and future climate. 


16 July 2014

Illuminating Behaviour


This blog post was written by postgraduate student Davena Watkin as part of the course, Research Methods in Ecology (Ecol608). Davena revisits a Lincoln University research area that looks at a study of how possums respond to moonlight in 2011.


The moon has a face like the clock in the hall;
She shines on thieves on the garden wall,
On streets and fields and harbour quays,
And birdies asleep in the forks of the trees.

The squalling cat and the squeaking mouse,
The howling dog by the door of the house,
The bat that lies in bed at noon,
All love to be out by the light of the moon.

 excerpt from The Moon by R. L. Stevenson

For our species, the moon is a theme of many literary and cultural ideas. And it's more than just waxing lyrical; we also have a long history of attributing human behaviour to moon phases. Calling someone a lunatic’ is a reference to the historic belief that prolonged exposure to moonlight caused insanity and epilepsy. In folklore, a full moon in some instances could also mean turning into a hairy, rampaging beast; lycanthropy is popular in many modern fictions.

Morepork: a native nocturnal predator.
Photo by russellstreet
As it turns out, ecologists are similarly fascinated with the effects of lunar light on behaviour, though for more down-to-earth reasons. Light, including moonlight, is an important regulator of the circadian rhythms of animals. Nocturnal animals are known to alter their foraging behaviour under higher levels of illumination, and such studies have their own moon-related jargon. Animals that avoid moonlit nights are known as ‘lunar phobic’, while animals that are more active on moonlit nights are known as ‘lunar philic’. 

Typically, small terrestrial mammals that are preyed on by higher-order nocturnal predators exhibit lunar phobia, while the opposite is usually true of their predators. In fact, contrary to Robert Louis Stevenson’s poem, mice and some bats are both lunar phobics. Lunar phobia is thought to be a form of predator avoidance, as more light increases the ability of visual hunters to detect prey.

The Ecology Department at Lincoln University have their own literary works on such behaviour. A recent example is a study that was undertaken by University of Göttingen masters student, Jessica Parisi, in 2011. The research sheds new light on the activity levels of brushtailed possums (Trichosurus vulpecula) in New Zealand under full moon and new moon phases. 

Brushtailed possums are native to Australia, where they are preyed on by snakes, eagles, foxes and dingos. As such, Australian possums display anti-predator behaviour by avoiding well-lit open areas. It was expected that the possums in Jessica's study would therefore be more active during new moons

New Zealand possum nocturnal behaviour:
a dramatic re-creation of the study findings.
Picture from Jeff Carter (modified)
In fact, Jessica found the opposite: that possum activity was lessened during new moons in forested areas. Possum activity was also still high in open scrub-land even during full moons.

Possums are perfectly capable of clambering around tree tops in the dark, so possum foraging strategies must have changed since their introduction into New Zealand. Jessica's results suggest that New Zealand possums don't need to be lunar phobic to avoid predators. Possums don't have many predators in New Zealand, but young possums are sometimes preyed on by feral cats. The feral cat is an ambush predator. It is likely that a preference for high visibility prevents a possum from being attacked out of the black by feline foe.

Caught on camera trap: possums 
interacting with wax tags, which
are used to monitor possum density.
Photo from Parisi, 2011
Brushtailed possums make regular appearances on this blog for one big reason: they are a notorious pest in New Zealand. As opportunistic omnivores, they cause significant tree defoliation and pose a threat to large endemic invertebrates and native chicks. Their widespread distribution also facilitates the spread of bovine tuberculosis. Hence, a great deal of research goes into finding the most effective ways to control possums in New Zealand. Pest management policy mandates that possum density is kept below a certain threshold and, as such, continual monitoring of possum numbers is required to show how effective ongoing control methods are and when further control needs to be undertaken. 

This research has important implications for the timing of possum control. Poisoning and trapping during times of greatest activity will conceivably increase possum encounter rates with control measures. Control operations may therefore achieve threshold values faster if populations are targeted during peak lunar phases. Similarly, monitoring using indirect measures should achieve greater precision if standardised to particular times of the month. Focusing control on open areas may also be particularly beneficial regardless of moon phase. 

More than anything, the study highlights the importance of behavioural studies for applied ecology. "Unless we fully understand pest animal behaviour, how can we effectively manage them?" asks James Ross, the supervisor of the study. Spoiler alert: we can’t. Behavioural ecology is essential for informing conservation and pest management, and helps us sort fact from fiction. As such, it is a valuable scientific pursuit. To believe otherwise is lunacy.


"AWOOOooo!" 
Picture by DCW
For more works from Lincoln University on the effect of the moon on behaviour, including the one discussed here, see:

Lennon, J. S. (1998). The Effect of Moonlight Intensity and Moon Phase on Feeding Patterns of Common Brushtail Possums. (Master's thesis, Lincoln University, 1998.) Retrieved from http://hdl.handle.net/10182/3062
 

Parisi, J. D. (2011). The Influence of Lunar Phase on Indirect Indices of Activity for the Common Brushtailed Possum (Trichosurus vulpecula) on Banks Peninsula, New Zealand. (Unpublished master's thesis). Lincoln University, Lincoln, New Zealand.