I guess I was always destined to spend my life in evolution and ecology. I distinctly remember from an early age, as I read through The Hobbit and The Lord of the Rings, worrying about the orcs. Not whether they are scary and nasty, that was a given, but rather how they fit in with the ecology of Middle-earth.  Questions like are orcs and goblins subspecies of the same species (which is implied in TLOTR as the goblins of the Misty Mountains are referred to as orcs in Moria) or are they separate species? Could they hybridise? How are their incredibly large populations sustained in such nutrient poor landscapes? Do they engage in niche construction by ruining the local landscape and driving out diversity, making it better for themselves? But most of all, how come orcs aren’t found in forests?

Orcs are primarily encountered in alpine areas (the Misty Mountains, Mountains of Shadow). Late in The Hobbit we hear that “ever since the fall of the Great Goblin of the Misty Mountains the hatred of their race for the dwarves had been rekindled to fury.  … Tidings they had gathered in secret ways; and  in all the mountains there was a forging and an arming. Then they marched and gathered by hill and valley, going ever by tunnel or under dark, until around and beneath the great mountain Gundabad of the North, a vast host was assembled“.

When orcs are found in places other than at altitude they are usually on a mission and have marched from mountains to places like Rohan, Gondor, and the Lonely Mountain. They don’t seem to live in forests. Not in the Old Forest, Fangorn or Mirkwood (although possibly in southern Mirkwood where it is mostly swamp). It struck me as a lad that there were no forest orcs. For such an invasive species this seems like a peculiar oversight. Surely orcs would love forests? Plenty of food, plenty of places to skulk, plenty of places to ambush those stinking elves, heck they could eat plenty of roast giant spiders every week (and who wouldn’t want to do that!).

Species distributions, where we find populations across a landscape, are built on a number of factors. A key trait is how populations are able to disperse and colonise. For a disperser to be successful they need to safely arrive at a new habitat, find food and water, avoid predation, find a mate (who has done the same), successfully mate and raise offspring (who also need to be able to do all of these things). This is not a trivial exercise and helps to explain why we don’t find everything everywhere.

Simply moving into a new habitat can be difficult and not all habitat borders are going to be equally permeable (crossable). Questions of how species move around and establish are of utmost importance in our modern world. In New Zealand we have many issues with invasive species. They outcompete our native species, modify habitats and provide support for other invasive species to become new problems. As such we are very interested in how species move around our slice of Middle-earth.

A common and problematic group of invasive plant species in New Zealand is the genus Hieracium. These small plants tend to spread through dry parts of New Zealand where they often dominate the local habitats. Jon Sullivan, with student Alice Miller and colleagues Susan Wiser (Landcare Research) and Richard Duncan (University of Canberra), wanted to know how this species was able to colonise the local landscape. They focused on a valley/pass that runs through the Misty Mountains (or Southern Alps) with most of their effort at a place called Craigieburn. They followed streams from the valley floor back into the local mountains and placed regular transects (or search areas) that moved from the streams into the surrounding habitat (forest or open alpine grasslands). They then searched for Hieracium.

What they found, in research published in New Zealand Journal of Ecology, was that streams seemed to serve as highways for Hieracium to move from one habitat to the next. The sides of streams are in a constant state of disturbance from floods. Invasive species generally do well in disturbed habitats compared to established habitats where they have to compete with established species. Hieracium make the most of these challenging conditions to spread along this marginal habitat. They also found that Hieracium was far less likely to be present in forest beside the streams compared with the alpine grasslands upstream.

So Hieracium makes use of streams to extend their distribution and are more likely to colonise alpine areas than they are to colonise forest areas.  Alpine grasslands are more permeable than forests to these invasive species and streams make all habitats more accessible. This type of information can certainly help us to manage these plant pest species. We can build a good idea of what is required to limit the spread of a species if we know what enhances their ability to colonise.

Maybe Middle-earth orcs are the same? Orcs may be a pest species that spreads around the environment, using streams and rivers to colonise mountain areas but finding forests difficult to break into and compete against local established species, like giant spiders, ents and stinking elves. That might be one question from my childhood answered. Now if I could only get some DNA from the goblins of Moria and the orcs of Mordor.