[Taxacom] Propagation of invasive species definitions

Stephen Thorpe stephen_thorpe at yahoo.co.nz
Sat Sep 11 19:12:47 CDT 2010

Well, I still think that scientists often don't understand the definition of 
"definition", which is ironic in this case, because I think taxonomists 
often don't understand how to classify concepts like the concept of invasive 
species! In science, the term "definition" is often used in a stipulative sense, 
to fix one precise meaning of an ambiguous term, but this often slides into just 
using any old term for anything provided you stipulate a precise definition to 
define how you are using it. This seems OK in some contexts, but not in others. 
For example, I could create a website and call it "a comprehensive database of 
the world's zoological biodiversity", but somewhere in the fine print I could 
define "zoological" as "entomological" (a subcategory of zoological). I don't 
think many people would be too impressed by this! But it is no different to 
defining "invasive species" as that subcategory of invasive species which invade 
new habitats and decrease native biodiversity, and yet this seems OK (to some 
people)! In analytic philosophy, the definition of a term is an attempt to 
capture (as opposed to stipulate) its meaning. It seems to me that scientists 
often confuddle (my word!) these two senses of "definition". The Global Invasive 
Species Database (ISSG), which operates out of the very building in which I now 
sit, only deals with invasive species in this restricted sense, so excludes many 
species which are expanding their range through the world and wreaking havoc in 
some other way (like chewing agricultural crops, etc.) This just seems all wrong 
to me. Instead of defining "invasive species" as those which invade new habitats 
and decrease native biodiversity, one should just say something like "the scope 
of this database includes only those invasive species which invade new habitats 
and decrease native biodiversity". While this may seem like a pedantic 
distinction, it avoids tremendous confusion when people try to compile 
glossaries giving the definitions of terms like "invasive species". As for 
invasiveness vs. naturalization, again I would say that an invasive species is 
just an unwanted naturalized species - there is an element of "negative 
consequences" in invasiveness, and this is best made more precise in terms of 
"unwanted consequences". For example, here 
(http://species.wikimedia.org/wiki/Arthurdendyus_triangulatus) is a N.Z. 
flatworm which has invaded Britain and is a predator of earthworms in 
agricultural systems, but doesn't rate a mention in ISSG, though someone has 
added it here (http://en.wikipedia.org/wiki/List_of_invasive_species_in_Europe), 
so it seems we have considerable diversity of definitions!

From: Frederick W. Schueler <bckcdb at istar.ca>
To: taxacom at mailman.nhm.ku.edu
Sent: Sun, 12 September, 2010 1:26:06 AM
Subject: Re: [Taxacom] Propagation of invasive species definitions

On 9/11/2010 12:16 AM, Stephen Thorpe wrote:

> Fred, Fred, Fred ... OK, start again:
> let us assume (for the sake of sanity!) that the meaning of the term
> "invasive species" is not idiomatic, i.e., assume that its meaning is
> the conjunction of the meanings of its constituent terms, "invasive" and
> "species". Lets also assume that we kind of know what "species" means.
> So, the question now becomes: what does "invasive" mean? Well, it means
> having a tendency to invade. What does "invade" mean? Well, it is a bit
> vague, but it would seem to involve a group of agents entering a new
> area in considerable numbers, and having some sort of significant
> unwanted effect...

* okay, the question is, what is invaded? At least in Canada, again, in 
the late 1980s and early 1990s, the original idea was that it was 
habitats otherwise undisturbed by people that are invaded, so that 
"invasive" species don't include those that malacologists call 
synanthropic, however abundant these may be. The metaphor was that the 
invasive species marches into the woods or wetlands on its own, like an 
invading army conquering territory, rather than being set up by overt 
human creation of its habitat.

On my 2007 invasive species page - http://pinicola.ca/limvade.htm - I 
suggested that "Humanity is not just a single species: Homo sapiens is 
always accompanied by a surrounding community of mutually dependent 
symbionts: domestic, inquiline, feral, pathogenic, or weedy, and in 
Canada only certain of these escape to wreak havoc in natural 
communities."  For the previously recognized kinds of exotics, humanity 
is the invader, and the synathropic species is just a camp follower. Are 
crop species invasive? - they've beguiled humanity into vastly expanding 
their ranges.

My suggestion that the definition of "invasive species" be based on a 
"quantitative decline in biological diversity" is just an attempt to 
quantify the fact of invasion, and the "takeover" of the invaded 
habitat, not to embody this as an "unwanted effect" of the invasion - 
though these declines in biodiversity are obviously often an unwanted 

When was the term "invasive species" first used in New Zealand?

(I've got very tenuous web connection here, so I haven't checked the 
suggested websites)


> a Google search for "invasive species" reveals all sorts of stuff:
> this one is interesting: http://www.isinz.com/
> 'Invasive species are a major factor in the decline of indigenous
> biodiversity around the world'
> this can be true without it being true BY DEFINITION, and I think so. I
> think that "invasive species" are just species with a tendency to invade
> new areas. This is the definition. It so happens, in fact, that many
> such species have negative impacts on biodiversity. This is true, but
> NOT part of the definition.
> Stephen
> ------------------------------------------------------------------------
> *From:* Frederick W. Schueler <bckcdb at istar.ca>
> *Cc:* taxacom at mailman.nhm.ku.edu
> *Sent:* Sat, 11 September, 2010 2:09:49 PM
> *Subject:* Re: [Taxacom] Propagation of invasive species definitions
> On 9/10/2010 8:47 PM, Stephen Thorpe wrote:
>  > on second thoughts Fred, perhaps your proposed definition:
>  > "a colonizing species which, in a particular area, causes a quantitative
>  > decline in biological diversity in habitats it colonizes."
>  > does capture something that mine doesn't which people tend to mean when
>  > they talk about "invasive species", namely that the negative effects
>  > must have something to do with a decrease in biodiversity, HOWEVER, two
>  > points:
>  > (1) looks like species released for biological control might count as
>  > "invasive species" by your definition, since they do cause a
>  > 'quantitative decline in biological diversity in habitats they
>  > colonize'. But such species are not unwanted, so don't count as
>  > invasives by my definition.
> * but if they succeed, and make invasive species or a weed/pest species
> less dominant in a habitat, they'll increase biodiverisity, since
> conventional biological control never results in the extinction of the
> target species.
>  > (2) that aside, what factors make my definition "better" than yours, or
>  > vice versa?? If your definition is accepted, then we don't have a term
>  > for what I am calling "invasive species", i.e. basically pest species
>  > that are moving around as opposed to staying put, but this is arguably
>  > an important concept to have a term for.
> * one could call it a weed or pest that's expanding its range, or
> becoming more common. "Pest" or "weed" is the noun, "increasing in
> abundance" is just a modifier.
>  > On the other hand, if my
>  > definition is accepted, then we don't have a term for pest species which
>  > tend to decrease (native, wanted) biodiversity in areas that they
>  > colonize, as opposed to those which might have other negative effects
>  > like causing itchy bites or undermining building foundations. The
>  > question is: do we need a special term for "invasive species" in your
>  > more restricted sense, or can we just deal with them in the same way as
>  > for species with other negative effects?
> * the idea of my definition is to preserve, and quantify, the original
> idea of invasive species when I heard the term first used: at least in
> Canada it was used for alien species that colonized otherwise
> undisturbed habitats and made native species less common than they had
> previously been. This (again in North America) was a striking overthrow
> of the then-conventional idea that all that was needed for conservation
> was the protection of habitat from direct human disturbance, and it was
> a new concept that these exotic species could "force their way into"
> nature preserves or other protected habitat.
> The term was so catchy that before it was adequately defined it was
> broadened to include alien forestry pests, agricultural weeds, and
> exotic species in other already-disturbed habitats. The situation is
> much different in New Zealand and other island biotas where alien
> species have long been known to crowd out otherwise undisturbed
> indigenous species - but when did these begin to be called "invasive?"
>  > I guess it comes down to
>  > whether we have dedicated teams of people who focus just on
>  > control/study of pest species which reduce biodiversity ... they might
>  > like a special term to express what they do ...
> * and that term, in Canada, was "invasive species," though since
> invasive species, in my sense, don't necessarily directly degrade human
> interests, I'd question whether most of them should be called "pests."
> fred.
> ---------------------------------------------------
>  >
>  > ------------------------------------------------------------------------
>  > *From:* Frederick W. Schueler <bckcdb at istar.ca <mailto:bckcdb at istar.ca>>
>  > *To:* taxacom at mailman.nhm.ku.edu <mailto:taxacom at mailman.nhm.ku.edu>
>  > *Sent:* Sat, 11 September, 2010 2:07:40 AM
>  > *Subject:* Re: [Taxacom] Propagation of bad sameAs statements or
> definitions
>  >
>  > On 9/10/2010 2:28 AM, Stephen Thorpe wrote:
>  > > well, I did seriously offer a definition of "invasive species", viz.
>  > >
>  > > an invasive species is one which has a definite tendency to expand
>  > its range
>  > > into areas where it is unwanted
>  > >
>  > > Definitions which define them in terms of particular or general
> "negative
>  > > effects" of the species are not good, because there are a great many
>  > > possible particular effects and the general concept is not
>  > well-defined, unless
>  > > you define it as an "unwanted effect", and then with a bit of
>  > simplification you
>  > > get my definition. Basically, it is invasive if border control wants
>  > to keep it
>  > > out ...
>  >
>  > * I've poked my oar into this one on the aliens list without converting
>  > anybody, but the anthropocentrism of all the widely used definitions of
>  > "invasive [alien] species" really annoys me, since many of them are
>  > effectively the same as the definition of "pest," or no different from
>  > "naturalised alien species."
>  >
>  > I've tried for a biocentric definition of invasive as: "a colonizing
>  > species which, in a particular area, causes a quantitative decline in
>  > biological diversity in habitats it colonizes."
>  >

          Frederick W. Schueler & Aleta Karstad
Bishops Mills Natural History Centre - http://pinicola.ca/bmnhc.htm
now in the field on the Thirty Years Later Expedition -
Daily Paintings - http://karstaddailypaintings.blogspot.com/
    RR#2 Bishops Mills, Ontario, Canada K0G 1T0
  on the Smiths Falls Limestone Plain 44* 52'N 75* 42'W
    (613)258-3107 <bckcdb at istar.ca> http://pinicola.ca/


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