Rare species

[Don McAllister]

Geoff Read wrote:
>
> > IUCN has recently revised the species at risk categories. They can be
> > through the IUCN home page. ...
>
> > ... So its not necessary to re-invent what is meant by rare. ...
>
> I see something at:
>
> http://www.iucn.org/themes/ssc/redlist/categor.htm
>
> Is that the page? It appears to be about endangeredness rather than
> rarity as such.
>
Yes that's it, and vulnerable is the equivalent of rare. Amongst other
criteria are:
Declining rate of 20% in 10 years or 3 generations
Extent of occurrence less than 20,000 square km
Extent of occupancy (species occupy only a part of the area
   within their range) of less than 2,000 square km
and other potential criteria involve: small population size, very small
number of mature individuals or extinction calculaltions.

So there is more than one way to classify a species as vulnerable. The
same goes for other higher or lower states of risk for a species. So the
system is flexible. It has also been tested out on hundreds of species.

don


--
Don E. McAllister             /& Canadian Centre for Biodiversity
Ocean Voice International          /Canadian Museum of Nature
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