Defining an Invader
The Northern Pike. Although it’s native to Norway, it has been moved around since and is now classified as ‘regionally invasive’. (Image Credit: Jik jik, CC BY-SA 2.0)
Two weeks ago, Norwegian Science Institute Artsdatabanken (ADB) announced that they would be changing the name of their invasive and alien species index. Formerly known as the Black List, the institute decided to use a name with less negative connotations, “Fremmedartslista“, loosely translated, the Alien Species list. Given this series’ focus on species from that list, it seems like an appropriate time to look at how we define the terms ‘alien’ or ‘invasive’ species.
What constitutes an invader?
The definition I’ve used thus far has been fairly simple – a non-native species that has a negative influence on some aspect of the area it invades, be that by reducing biodiversity (like the Red King Crab or Garden Lupin), affecting human health (like the Common Ragweed) or impacting the economy (like the Canada Goose). This is almost identical to the definition formalised by the United States in 1999, which stated that an invasive species is “an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health“. My own government’s Department of the Environment and Energy dictates that an alien species must threaten “valued environmental, agricultural or other social resources by the damage it causes” to be considered invasive.
However, at the beginning of this series we introduced ADB’s Fremmedartslista, which is a self-confessed “purely ecological impact assessment”, and does not account for any potential effects on the economy or human health. All Norway’s invasive species are on this list, yet not all species on the list are what the aforementioned government definitions would consider ‘invasive’. Some have had limited impact as their range has been limited, and others have shown little ecological effect thus far. It is important to be aware of these species though, as often an invader’s ecological impact is not fully understood until it is well established.
It’s important at this point to note that definitions of an invasive species vary based on the organisations they come from. ADB’s list is intended to be a neutral knowledge source from a science institute, to be used for management decisions. The US and Australian governments are ostensibly institutes which take care of their citizens, so naturally effects on the economy and society are also crucial. Yet is it wise to grant one organization control of all such categorization, particularly when ecological and economic priorities come into conflict?
And what does ‘alien’ mean?
This may seem like the simple part of the definition, but there is still some ambiguity here. We have already covered the fact that the wild boar and many predators were once native to Norway, and have recently been making their way back in. Both the boar and the musk ox are listed by ADB as alien, having been locally extinct before 1800. And climate change now means that some species which are native to certain parts of Norway are moving north, as habitats which were previously too cold become warmer. ADB now lists the northern pike as ‘regionally alien’, a species which has significant negative impacts on other native fish species. It is native to the south of Norway, and has been moving north, causing local extinctions of many fish species.
On the other hand, there are species worldwide which have been long established which were initially alien. There is some debate remaining over whether the Australian dingo should be considered alien, although most ecologists agree that any ecological effect of the dingo’s introduction has long since taken hold.
It’s also important to point out here that ‘alien’ isn’t necessarily a negative term. Whilst it may, 20 years later, still conjure up images of a certain movie that I should definitely NOT have watched as a 9-year old, there has been a push recently away from the alien-versus-native species dichotomy, spearheaded by Professor Mark Davis, who I’ll be speaking to in the coming weeks. I recommend reading Mark’s 2011 article on the subject.
Where to from here?
Lara Veylit has already written about rewilding at length in this series. But this is just one example of when ecological benefits clash with societal or economic priorities. The Red King Crab is an obvious case where an economic benefit is accompanied by a marked drop in biodiversity, as is the Sitka spruce, which we’ll profile on Monday. So how do we gauge conflicts of interest, and who should manage them? Lara will address this next week.
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