Rare species

[Thomas G. Lammers]

At 09:19 AM 07-29-97 -0700, Dennis Paulson wrote:

>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.

I disagree.  From a conservation perspective (which, after all, is the arena
in which rarity is most discussed), a widespread low-density species may
have a more secure future, and be in better shape in terms of genetic
diversity, than a species restricted to a few places or to a specific
habitat that (originally or through human intervention) only occupies some
small percentage of the world's surface.  The danger of putting all one's
eggs in a single basket.

>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.

The argument I've heard advanced for state rarity lists goes something like
this: such species on such lists are often outliers or peripheral
populations on such species, and it is often in these somewhat isolated
populations that "interesting" evolutionary things occur.  Thus, to preserve
the total diversity of a species, such semi-isolated populations may be more
important than more centrist populations.  I'm not sure there's a lot of
data to back this view up, and I'm not particularly enthused over
geographically delimited lists of imperiled species.

On the other hand, given the numerous threats confronting natural
populations, its probably better to err on the side of bestowing coveted
"rare" status too liberally, if that's what it takes to save them.   I'm
reminded that the much-beloved  Hawaiian naturalist and
conservation-evangelisr Otto Degener once suggested that ALL  endemic
Hawaiian species be red-listed as Endangered, and only moved to a blue-list
or safe-list once data had shown such status to be unwarranted.


Thomas G. Lammers

Classification, Nomenclature, Phylogeny and Biogeography
of the Campanulaceae, s. lat.

Department of Botany
Field Museum of Natural History
Roosevelt Road at Lake Shore Drive
Chicago, Illinois 60605-2496 USA

e-mail:     lammers at fmppr.fmnh.org
voice mail: 312-922-9410 ext. 317

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