20 October 2014

Winning the battle for our birds (but losing the war?): 1080, rats, possums and the NZ bush

Sometimes common sense is not actually our friend. In our society common sense is usually seen as a virtue that those so-called experts could do with more of. But common sense can fall down on the common side of things. The All Blacks have gone into every rugby world cup as the favourites to win over all. They have won only two. This is a case where 'common' is a statistical concept in which there is a higher likelihood of something happening, but no guarantee that it will happen. Common sense can also fall down on the 'sense' side of things as well. Looking at our modern lifestyle it seems obvious that we are much less active than our ancestors would have been. It's no wonder we have issues with weight in our societies. However, data points to the fact that we are actually just as active as our hunter-gatherer ancestors and we need to look at other reasons for obesity. This is a case where 'sense' is a statement that needs data to confirm it. So although common sense is a useful concept, allowing us to make predictions based on experience, it can be misled through probability and through not having correct facts. Common sense is particularly a problem when we are faced with emotion-charged debates. In New Zealand one of the more emotionally charged debates is with the use of toxins to kill mammalian pest species, like rats, possums and stoats, at very large scales.
There's a whole lot of seeds up there!

The southern beech (Nothofagus) forests of New Zealand are prone to heavy seed crops every 4-6 years (known as a beech mast). Mast events provide a huge amount of food for rodents whose populations swell over the next few months. With the rise in rodent numbers we get a similar, though slower, response by their predators, particularly the stoats (a mustelid). The following year is almost never a mast event and so rodent numbers crash as there is not enough food around. The inflated predator population will continue to eat rodents where they can but, with the rodent population decline, they often switch to other prey. In New Zealand this other prey is mainly birds, and in beech forest these are usually native species. So a mast event will usually lead to a massive reduction in bird populations the following year, when the stoats get hungry. This year has been a mast year in our beech forests. What can we do to ensure that our threatened bird species are not decimated over the next year?

The Department of Conservation has launched the 'Battle for our birds' campaign. Common sense would suggest that if we could keep the rodent numbers down during the mast event, then their populations will not increase and, therefore, stoat numbers will not increase as a result. So, no  problems for birds next year. Department of Conservation are delivering the toxin 1080 to several hundred thousand hectares of key beech forest habitat throughout New Zealand this year. The toxin is dropped into the forest where is can be encountered by rodents (usually rats) who will store some of the cereal bait, eventually consuming a lethal dose. Stoats eating recently dead rats may also accumulate a lethal dose and their populations don't increase as their food supply does not increase. Happy birds in 2015. Problem solved.

Rats: In action on the forest floor

Maybe. There are a number of studies now that have looked at the long term effects of intense control of mammal pest populations. In a seminar at the Department of Ecology, Lincoln University, Dr James Ross talks through a couple of studies that he has been involved with which looks at what happens to populations that have had pest control done. Long-story short (but you should listen to that entertaining talk!), 1080 does a great job of knocking down rodent and possum populations (and stoats as a by-product). The forests habitats respond positively to the removal of the pests, particularly the small bird species. However, different species recover at different speeds. Mice are not particularly troubled by toxin drops (as rats are usually dominant and grab the baits) and their numbers begin to grow after control as they have no competition from rats. This is not such good news for forest invertebrates that are in the food size range of mice. After a few years, the rat populations start to bounce back (mostly by re-invasions from the edges of the control areas) and at a much faster rate than stoats. So there is a period of time where rat populations will not be checked by stoat predation. So will the battle for our birds work? It depends on the timeframe and what follow up work is done. Control will certainly put a break on rat (and then stoat) populations and preserve bird populations in the following year, that's just common sense. However, if follow up control of rats is not done after three or so years then rat populations may rebound ahead of their predators and we will have a problem similar to that of a mast season occurring, lots of rats that lead to a surge in stoats. So we might win the battle but lose the war if we are not careful. And that, perhaps, isn't such common sense.

13 October 2014

Tolkien made me an evolutionary biologist

I've been an evolutionary biologist for over two decades now and I have been reflecting recently on how I came to join this profession. I started re-reading Stephen Jay Gould's Ever since Darwin, Goulds first collection, and have to acknowledge that Gould's amazing essays played a role as an undergraduate. Darwin's On the origin of species was also influential around the same time. Dawkin's The Selfish Gene was one of the first science books I read, so that has to be part of it. But, really, I have to go back further as I arrived at university with the passion for zoology and evolution already forming. In fact I can go back to when I was about 9 years old and read The Hobbit, followed by The Lord of the Rings a couple of years later. That's where it started.

Tolkien and evolution. These are not things that normally go together. Tolkien has often been portrayed as a romantic, always looking at the good old days, anti-technology and progress (especially by sf author David Brin). And this is hard to argue against. However, and perhaps ironically, there are many themes in Tolkien that help to prepare one for a life in evolution.

Min: The journey is important.
Summarising The Lord of the Rings as "short tourist loses valuable heirloom at volcanic destination" loses the whole sense of the journey, which is actually what the story is about. All the characters change (or evolve) significantly during the story. Evolution is about the journey, exposing the history of lineages. Ecology is about the destination, looking at the interactions that are here now. Tolkien helped my young mind to understand that everything has a history and that this journey is important.

Tad: Lineages are important.
Tolkien loves his genealogies. Frequently in his writings we are told who is related to who. It matters that Elrond has links to certain elven and human lineages. There are lineages in his appendices. This was a revelation to a young me. Relationships are important. Closely related characters respond in different ways to distantly related characters. Tolkien helped my young mind to understand that everything has a history and that lineages are important.

Neledh: Spatial scale is important.
Tolkien loved maps. One of the cool things to a nine year old was the map in the front of The Hobbit (as well as the runes!). Even in an imaginary world it matters where things are. It matters that the Lonely Mountain is on the Long Lake or that the Misty Mountains need to be crossed to get to Mirkwood. It matters that Farmer Maggot's farm is next to the Buckleberry Ferry. Tolkien helped my young mind to understand that where things are located spatially is relevant to explaining the journey.

Canad: Species distributions are important (as is how they came about).
Part of Tolkien's fascination with maps is that he uses them to explain where races are located. You learn about the distribution of dwarves, hobbits, elves and so on. You also learn about how these distributions have changed over time. Tolkien had detailed notes on the dispersal of races. For example, the hobbits had colonised The Shire relatively late in the piece, dispersing from Bree and prior to that from the shores of the great river Anduin across the Misty Mountains. Tolkien helped my young mind to understand that species move around, that what you see today has not always been the case, and that dispersal is a powerful force.

Leben: Landscapes are not permenant.
Tolkien presented different eras. The Lord of the Rings is set at the end of the third age which had been going for 3000 years. Two long ages preceded this one, giving a perception of deep time. Moreover, even the continental landscapes had changed during this period. Large parts of western Middle-Earth had submerged beneath the seas, cataclysmic battles had raised mountain ranges. Tolkien helped my young mind to understand that there is no long term permanence in geological features.

Eneg: Diversity is important.
Tolkien valued diversity. It is no accident that the fellowship is successful because it is made up of different races, each with skills that help achieve the final goal. Or that it is the hobbit joining the dwarven company that makes the difference. Tolkien also invented languages (I have used elven numbering here!) to emphasise this diversity. Tolkien helped my young mind to understand that diversity creates useful outcomes.

Tolkien was an author that pushed the importance of lineages, history, spatial scale, species distributions and dispersal, landscape impermanence and diversity through all of his stories. If this is not the ideal preparation for a young evolutionary biologist (especially one who specialises in biogeography) then I'm not sure what is!

Namárië !