Rare species

[Dennis Paulson]

How about an operational definition something like "present in such low
numbers that one could not be guaranteed of finding it on a visit to its
preferred habitat, using the best methods known to detect the species." I
study dragonfly biodiversity, and I can easily distinguish species in this
category. This definition can be used at any scale, from a species rare at
a given location to a species rare everywhere in its range. It would not
apply to a species fitting your first criterion of geographic or ecological
restriction, at least not where it is common; however, it would apply to
widespread species at very low density. Surely low density is one of the
most significant criteria for rarity, as it relates directly to the
stochastic issues of sex ratios and mate finding.

There has been quite a bit of discussion about rarity and political
boundaries, about the value of considering species that are rare in a
political unit, e. g., rare in an American state even though common
elsewhere in the U. S., worthy of special concern. Most state wildlife
agencies and conservation groups seem to consider this status very
seriously. Rarity at any scale, even rarity in a particular urban area of a
species common in the nearby countryside, seems to endow a species with
special status, for better or worse, and I suspect the concept of rarity
will remain rather subjective and parochial.

One reference on local rarity that I recall is a discussion by Malcolm
Hunter and Alan Hutchinson in Conservation Biology 8: 1163-1165, 1994.

>Dear Taxacomers
>
>Would anybody like to define what they consider the adjective 'rare' (as
>applied to a species) to mean? This term crops up more frequently nowadays,
>generally in pleas to public bodies to preserve habitats.
>
>I have always considered the term to be meaningless, since it covers
>species whose habitats are restricted geographically or ecologically (i.e.
>common where it occurs), or widespread but at low species numbers, and is
>possibly only really applicable to species close to extinction (but then
>this is normally due to the loss of habitat anyway).
>
>Is there a discussion somewhere that someone could point me to?
>
>Thanks
>
>Paul Selden

Dennis Paulson, Director                           phone 253-756-3798
Slater Museum of Natural History                 fax 253-756-3352
University of Puget Sound                       e-mail dpaulson at ups.edu
Tacoma, WA 98416
http://www.ups.edu/biology/museum/museum.html