Invasive aliens and other bad language

Himalayan balsam (Impatiens glandulifera).  Photo: Charlie Bell

This blog was migrated to this website on 17/02/15 from the previous Tomorrow's Biodiversity scratchpad website.

Growing media attention
A growing amount of attention is being given to biodiversity loss resulting from the introduction of non-native species. Introduced species that do well, especially if they do so at the expense native flora or fauna, are frequently referred to as ‘invasive aliens’.

A  feature on the BBC’s Countryfile programme a couple of days ago made a good comparison between the considerable amount of action and policy focussed on ‘invasive aliens’ and the little focussed on another driver of biodiversity loss – eutrophication caused, to a large degree,  by nitrogen pollution. But the impact of this comparison was lost because the focus then shifted to native plants that have responded to eutrophication by increasing in abundance, e.g. Nettles and Brambles. The presenter repeatedly referred to these plants as ‘native bullies’ giving the impression that they are directly responsible for biodiversity loss and obscuring the message that eutrophication is the true driver.

The programme inspired an article which appeared in the online Telegraph yesterday entitled “Defending UK from foreign species costs £26 per person”. This article completely ignored the problem of eutrophication and nitrogen pollution, only referring to it obliquely right at the end with a very confused reference to ‘native bullies’. The phrase had stuck, but the message was entirely lost.

For whatever reason, the author of the Telegraph article preferred the term ‘foreign invaders’ over ‘invasive aliens’. Foreign Invaders, Invasive Aliens and Native Bullies; it’s all very tabloid. You only have to look at some of the public comments on the Telegraph article – many of which draw irrelevant comparisons between the introduction of non-native species and human migration – to realise how unhelpful the vocabulary is becoming in this debate. It made me appreciate how careful ecologists should be about the language we use, especially when addressing wider audiences, and I have resolved, from now on, to talk about the problems of ‘biotic exchange’ rather than ‘invasive aliens’ wherever I can. (And if you ever catch me using the term ‘native bullies’ – except to say it’s a bad one – you have my permission to shoot me.)

What is biotic exchange?
Over the last few centuries our species has started to move around the planet with increasing ease and rapidity and, in doing so, we have introduced a large number of other species to areas of the planet that they would not have otherwise reached. This is the phenomenon of biotic exchange. Some of these introductions have been deliberate, but many more are unintentional (for example those transported in ship’s ballast). Many – probably most – of these introductions are benign, but sometimes introduced species are able to exploit a novel ecological situation to the detriment of native species which have not evolved to cope with the new competition and, in such situations, they can become problematic and a threat to local biodiversity.

What is eutrophication?
Since the industrial revolution our practice of burning fossil fuels has been releasing nitrogen and sulphur into the atmosphere which is then deposited over the surface of the land and sea, sometimes in places very distant from its source. Over the same period, but particularly since the middle of the 20th century, intensification of farming has lead to widespread use of nitrogen and phosphorous fertilizers which get into the wider environment, particularly through rainwater runoff. The consequence is a general increase in eutrophication over the land and at concentrated points in freshwater and marine ecosystems.  The Millennium Ecosystem Assessment stated that nutrient loading (including nitrogen, phosphorous and sulphur) “has emerged as one of the most important drivers of ecosystem change in terrestrial, freshwater, and coastal ecosystems, and this driver is projected to increase substantially in the future”.

The relative importance of biotic exchange and eutrophication
When I recently reviewed the scientific literature on the drivers of biodiversity loss for the Tomorrow’s Biodiversity Project, I concluded that the following drivers are currently considered to be most important in terrestrial, freshwater and marine ecosystems (with the most significant closest to the top of the lists).

Major global drivers of biodiversity loss in terrestrial ecosystems

  • land-use change (encompassing habitat loss, degradation & fragmentation);
  • climate change;
  • eutrophication;  and
  • biotic exchange.

Major global drivers of biodiversity loss in freshwater ecosystems

  • habitat degradation, including flow modification;
  • pollution, including eutrophication; and
  • biotic exchange.

Major global drivers of biodiversity loss in marine ecosystems

  • climate change (especially in coastal areas);
  • overfishing;
  • habitat degradation (e.g. from destructive fishing operations);
  • acidification; and
  • pollution (including eutrophication of estuaries).

Clearly both biotic exchange and eutrophication are regarded by ecologists to be among the most important drivers of biodiversity loss. But eutrophication is consistently identified as being more important – in many cases considerably more important – than biotic exchange in all major ecosystems. (And it’s worth noting that habitat loss & degradation are consistently identified as the greatest driver of biodiversity loss in terrestrial and freshwater ecosystems, positively dwarfing all others including biotic exchange and eutrophication.)

Communicating complexity
Communicating the problem of biodiversity loss and its drivers to the public is a real challenge for ecologists and the media. There’s no getting away from the complexity. When I want to remind myself about the complexity of ecological systems, I sometimes do so by reference to another set of complex systems that we are all familiar with – economic systems. Complex though economic systems are, I remind myself that ecological systems are many, many times more complex still.

Lots of useful comparisons can be made between economic and ecological systems. For me, one of the most sobering is that despite the attention we lavish on economic systems, our understanding of them is still extremely poor. We were all made painfully aware of this when, almost to a man & woman, our economic experts were caught with their pants around their ankles when the current global financial crisis came crashing in, apparently out of the blue, at the end of the last decade.

The lack of understanding and complacency surrounding those events are echoed – many times over – in our relationship to the ecological systems which support our existence on this planet and in the vocabulary we use to talk about them. When a complex system changes – as the global financial crisis has reminded us – it can do so with astonishing rapidity and violence. If we are to stand the remotest chance of avoiding changes in ecological systems which will make those we have experienced in our economic systems look like storms in a thimble, we need to get a handle on their complexity and communicate that effectively. We won’t do it by dumbing them down to the level of tabloid journalism.

Giant hogweed (Heracleum mantegazzianum).  Photo: Julia Makin