Questions about Extinction Criteria
All distinctions made below will
be reviewed and modified by CREO Advisory Panels.
did we handle subspecies?
We chose "species" as the basic
unit to count for practical reasons. It is the most widely accepted
and recognized biological unit, particularly in terms of having the
greatest acceptance and practical value to conservation policy. Thus,
we chose not to count "subspecies" or populations. If we include these
units, we risk producing lists that are too confusing and complicated
to be understood or used by relevant consuming groups.
did we use AD 1500 as a cut-off date?
For practical reasons, we defined
recent extinctions as those occurring since AD 1500. Extinctions after
AD 1500 represent those most pertinent to current biodiversity issues.
This date also marks a time when recorded evidence for the loss of species
in association with human movement and activities became more common.
However, there may be cases of earlier extinctions that are relevant
to the evaluation of current patterns and processes of extinction, and
these events will also be evaluated (e.g. extinctions associated with
Polynesian expansion 1000 to 4000 years ago; Pimm et al., 1994, 1995;
Steadman, 1995; Diamond, 1997)
wait 50 years before declaring a species' extinction fully resolved?
The 50 year rule was introduced
by CITES (Convention on International Trade in Endangered Species) and
the IUCN, but dropped from the 1996 IUCN Red List. We have re-adopted
it here as an insurance policy (albeit arbitrary) against prematurely
declaring a species extinct. We decided on this protocol because it
provides a lengthy time period during which the species, if still extant,
might be seen or collected, purely by chance. This can be particularly
important when it is difficult to judge whether sufficient sampling
has been conducted to confirm the species' absence. We are concerned
about wrongly declaring an extinction in situations where:
- the species is particularly
difficult to collect regardless of sampling -- for example, because
it is cryptic or naturally rare.
- the habitat is particularly
difficult to survey -- for example, marine environments.
- the species is temporally
absent from its typical habitat, but not extinct -- for example, when
environmental change or ecological shift result in the movement of
the species to a different, unexpected (and unsurveyed) habitat.
Use of the 50 year rule as
the only criterion for judging extinctions can lead to errors. Therefore,
we propose application of the 50 year rule in conjunction with other
about species that are functionally extinct, regionally extinct, or extinct
in the wild?
Some species have been described
as "functionally extinct," where only senescent and non-reproductive
adults represent the taxon. CREO will adopt a policy of drawing attention
to those species that are on an irreversible path to extinction, but
listing them separately from those species that are truly extinct.
Species-level extinctions refer
to the loss of all representatives of that species, such that the shared,
unique genetic heritage of that species has completely disappeared.
Species that have been extirpated regionally, or have been eliminated
in the wild but still exist in captivity, may have lost important genetic
material and/or may be in grave danger of extinction, but they cannot
be considered extinct. However, the regional extirpation of these species
can be measured using similar criteria as those proposed here.