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What is a natural freshwater ecosystem: invasions, aliens and novel ecosystems

November 2, 2010

Derwent Water in the English Lake District: the last remaining native habit of the vendace (Coregonus vandesius) which is predated by introduced populations of the non-native ruffe (image: wikicommons)

At first glance, defining a ‘natural’ ecosystem seems relatively straightforward.   However, on closer inspection, an understanding of the ecological, climatic and cultural histories of a landscape muddies the waters of identifying a set ‘natural’ ecosystem state.  Global ecosystems are in constant flux, influenced by both natural processes and human influence over thousands of years, which makes defining a natural state for their conservation or restoration difficult.

Writing in Freshwater Biology in January, David Strayer discusses the effects of biological invasions of ‘alien’ species into global freshwaters, creating new and ‘novel’ ecosystems.  Such invasions are becoming increasingly common, with species spread in ship ballast water (e.g. the round goby), through the aquatic trade (e.g. Canadian pondweed), deliberate introductions, and angler’s bait buckets (e.g. the introduction of ruffe in Scottish lochs).

Zebra mussels (image: wikicommons)

There are numerous economic, environmental and cultural services and benefits resulting from the conservation of biodiverse and distinctive freshwater ecosystems – see this short interview with BioFresh partner Dr. William Darwell for more details.   Allowing biological invasions to occur unchecked may lead to ecosystems becoming dominated by highly adaptable ‘generalists’ like the zebra mussel or the round goby, potentially at the expense of ecosystem diversity and function (dubbed the “Homogecene”).

Round goby (image: wikicommons)

Given that current ecological thought stresses how ecosystems are in a constant state of flux, it could be argued that we accept biological invasions as natural processes thathave occurred countless times in the past.  As Stephen Jay Gould describes, on an evolutionary timescale species are only native to a particular area through a series of chance events, and aren’t necessarily better adapted to their habitat than ‘non-native’ species.  However, the issue isn’t that biological invasions are still occurring – it is that their rate and magnitude is being significantly increased by human influence.

Returning then to the idea of what constitutes a ‘natural’ ecosystem, Strayer’s paper raises a number of important points.

The composition of global ecosystems are being increasingly reshuffled and altered.    Any attempt to conserve or restore a ‘natural’ ecosystem must be aware of these processes.     Strayer’s research suggests that freshwater ecosystems will continue to be flooded with new invasive species in the future, creating new ecosystem assemblages with no historical equivalent to guide their management.  His conclusion states “the best solution to the management problems caused by alien species will be to work aggressively to cut the arrival rates of new invaders”.

Canadian pondweed (image: wikicommons)

For Richard Hobbs and colleagues, biological invasions make us re-assess a stark distinction between ‘natural’ and ‘non-natural’ ecosystems – moving away from an over reliance on excluding alien species at all costs, instead focussing on appropriately managing emerging ecosystems .  This may seem like a defeatist approach, but as Hobbs and colleagues suggest, we are faced with an unprecedented rate of ecosystem change, making exclusion of new invasive species extremely difficult.

Responding to the comments on a draft of their paper, they conclude dryly that:

one reviewer commented that the examples[of novel ecosystems] are ecological disasters, where biodiversity has been decimated and ecosystem functions are in tatters, and that ‘it is hard to make lemonade out of these lemons’.

Our point is, however, that we are heading towards a situation where there are more lemons than lemonade, and we need to recognize this and determine what to do with the lemons”

How far do biological invasions make us re-assess what we term a ‘natural’ ecosystem?

Do you agree with Hobbs and colleagues that we should focus our conservation efforts on appropriate management of new and novel ecosystems rather than relying solely on excluding new invaders?

As ever, we welcome your thoughts.

More information:

7 Comments leave one →
  1. Jono1986 permalink
    November 3, 2010 10:23

    An interesting article, thank you.

    Aside from the obvious debate outlined above between managing these novel ecosystems or preventing species invasions, one thing struck me that appears to have been overlooked; that humans are invasive species par excellence. As a species, our ability to disperse and manipulate our surroundings is second to none. Take for example the exploration of the world’s highest mountains, deepest seas and even the moon.

    Therefore, I can’t help noticing the irony with which scientists talk about ‘controlling invasive species’, without considering the human predicament. Whilst the role of humans in spreading invasions may be significant (as outlined in your blog), I wonder whether there is a philosophical basis to the argument, rather than merely this ‘bean counting’ of invasive species numbers? What right, as the most invasive of all species, do we have to limit or control other species? Also on what basis, once an invasive species is established in an ecosystem (even if introduced by humans), do we have to eradicate it?

    I would very much welcome your thoughts on this seemingly ignored side of the argument.

    • November 3, 2010 10:46

      Good points – thanks for bringing them up.

      Whilst you’re absolutely right that humans are undoubtably the most successful biological invader, it could be argued that awareness of our damaging impacts on the world’s ecosystem carries with it a moral responsibility to reduce further harm (however paradoxical that might be)? However, this responsibility is likely to be overwhelmed by the economic and social imperitives to control invasive species.

      But your points are very pertinent – do humans have a right to control and define the species composition that makes up a ‘natural’ ecosystem?

  2. Jono1986 permalink
    November 3, 2010 12:03


    Yes I agree, considering that humans have the propensity to moralise we therefore are obliged to consider our impacts on the world’s ecosystems. However, not everyone would agree with this due to differing moral standards. My point is that there should be open debate regarding the morality behind the way that humans interact with ecosystems and nature. Are you aware of this occurring explicitly within the context of invasive species and novel ecosystems?

    In response to your comments regarding the economic and social imperatives to control invasive species overwhelming moral responsibility towards human interaction with ecosystems, biodiversity etc. Whilst I understand that urgent action must be taken, I do not see why moral standards and economic and social imperatives should be mutually exclusive, or that one should override the other. Moral standards and ideologies (e.g. utilitarianism) form the basis on which humans make rational decisions. If these standards are at odd with current actions and the global environmental predicament then perhaps a shift in social moral standards regarding human interaction with the environment is absolutely essential to amalgamate both people’s day-to-day lifestyles with the impacts they have on other species and ecosystems.

    Additionally, you mentioned the economic imperatives regarding ecosystems, or in other words ‘ecosystem services’. I fear that taking this very anthropocentric view of ecosystems may lead to serious future problems. Whilst the article above talks about invasive species causing serious issues in novel ecosystems, I could well see humans managing and creating novel ecosystems specifically to enhance or supply ecosystem services. For example, say an invasive mussel species enters a water body and establishes itself at the expense of native species, thereby generating a novel ecosystem. However, this invasive mussel is found to be extremely adept at filtering this water, much more so than any ‘native’ species. As such the freshwater is therefore much cleaner, dramatically reducing costs for water purification for human drinking water. This mussel has therefore provided a valuable ecosystem service but at the expense of ‘native’ species. Taking an ecosystem services approach without proper consideration for ‘native’ species etc could lead to humans deliberately creating or manipulating novel ecosystems solely to enhance services to humans. This approach would then lead to dramatic changes in species assemblages and richness. The concept of manipulating the environment solely to suit ourselves seems very wrong to me, and I’m concerned that we may be heading in that direction. Instead of a solution to environmental problems it may be that placing a monetary value on ecosystems will turn them into a commodity to be traded and exploited. Again, this comes back to morals and values. Instead of finding new methods under the old system, perhaps it is time to look at changing the system and the morals and values it is based on.

    • November 3, 2010 15:09

      Great points – thanks again.

      It’s interesting that you bring up the idea of the morals and values that underly how we think about the management of invasive species.

      It could be argued that the basis for the exclusion of non-native invasive species is rooted in concepts of equilibrium-based ecosystems under a “balance of nature” As such, invasives are seen as an unnatural disturbance to the status quo, not being part of the static and closed equilibrium-based ecosystem. Steve Trudgill (2001, 2008) has written about how concepts of what is ‘native’ and what is ‘alien’ have deep emotional resonance with many people – members of the public and conservationists alike – particularly set in the context of this perceived ‘balance of nature’.

      In fact, for Jonah Peretti (1998), there are paralells between conservation science’s ‘nativist’ bias against alien and invasive species and questionable racist or xenophobic attitudes. Whether you agree or not with Peretti, it is pretty sure that (like you say) conservation management is not simply a scientific discipline, instead highly influenced by our environmental ethics and values.

      Worth having a look at:

      Peretti JH (1998) Nativism and Nature: Rethinking Biological Invasion. Environmental Values 7: 183-92

      Shrader-Frechette K (2001) Non-indigenous species and ecological explanation Biology and Philosophy 16L 463–79

      Trudgill ST (2001) Psychobiogeography. Meanings of nature and motivations for a democratised conservation ethic Journal of Biogeography 28 677–98

      Trudgill, ST. (2008) A requiem for the British flora? Emotional biogeographies and environmental change. Area 40: 99–107.


  1. Welcome back: plans for the BioFresh blog in 2011 « The BioFresh blog
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