Craig Hilton-Taylor hiltonta at NBICT.NBI.AC.ZA
Thu Jul 31 09:08:08 CDT 1997

Paul Selden asked for a definition of rarity and a good reference on
the subject.

There are many definitions of rarity and a vast literature on the
subject. Perhaps the best and most recent overview of the subject is:

Kunin, W.E. & Gaston, K.J. (eds.) 1997. The Biology of Rarity.
Chapman & Hall, London.

This book examines many aspects of rarity, including how to define
it. One important aspect that comes through is that Kevin Gaston
stresses the need to separate considerations of threat from
definitions of rarity. He points out that failure to do this has been
a recurrent problem in conservation biology. This was one of the
problems with the old IUCN Red Data Categories which used the term
'rare' as one of the categories of threat. This term was widely
interpreted by people using the system. The new IUCN Red List
categories avoids the use of terms like 'rare' and 'rarity'.

>From Kunin & Gaston's book it appears that there is no standard
definition of rarity. This could pose a problem for comparative
studies, so Gaston argues for the adoption of a standard definition
which is simple and broadly applicable. He suggests classifying 25%
of species in any assemblage with the lowest abundances or smallest
range sizes as rare, regardless of how the parameters of abundance
and range size are measured.

Any comments?

Craig Hilton-Taylor

Craig Hilton-Taylor
Ecology and Conservation Research
National Botanical Institute
Private Bag X7                        Tel: +21 - 762 1166
Claremont 7735                        Fax: +21 - 797 6903
South Africa                        Email: hiltonta at nbict.nbi.ac.za

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