Biology Reference
In-Depth Information
equally instructive examples. Bahaman turtles of the genus
Trachemys
have
apparently not been native members of the fauna of the Great Bahama Bank in recent
times but may have been in the Pleistocene (Seidel, 1988, 1996). Until recently,
turtles from Cat Island and Eleuthera on this bank have been treated as an endemic
species and considered highly endangered (Groombridge, 1982). More recently,
they have been shown to be conspecific with the Jamaican species
T. terrapin
and
are presumed to be introduced (Seidel and Adkins, 1987; Seidel, 1988). However,
Lee and Ross (2001) argue alternatively that
T. terrapin
is native to the Great
Bahama Bank and prehistorically introduced to Jamaica. Taxonomic confusion
about Caribbean
Trachemys
persisted for many years because morphological varia-
bility within the genus had been difficult to assess. This was worsened in the
Bahamas by introduced
Trachemys
species creating hybrid swarms, resulting in
additional phenotypic confusion (D.G. Campbell, 1978; Groombridge, 1982;
Seidel and Adkins, 1987; Seidel, 1988). Foreign
Trachemys
species introduced
to the Bahamas include
T. stejnegeri
(Seidel, 1988),
T. terrapin
(Seidel, 1988),
T. decussata
(Lee, 2004), and
T. scripta
(Lee and Ross, 2001; Mealey et al., 2002;
Lee, 2004), and some of these introductions continue to be made (Mealey et al.,
2002; Lee, 2004). Because of this history of human intervention, taxonomic resolu-
tion of Bahaman
Trachemys
was delayed until populations on the Great Bahama
Bank were very small. The result is that, without clearer historical resolution of
directionality of movement for
T. terrapin
, it remains uncertain whether Bahaman
populations are endangered native elements or foreign interlopers, although the lat-
ter presently seems more likely.
Similar problems plague understanding of the giant tortoises of the granitic
Seychelles. It is clear that one or more species of tortoise was native to these islands
inasmuch as they were noted to be common when the islands were discovered
(Stoddart and Peake, 1979). However, these original populations were extermi-
nated, and tortoises from Aldabra were later imported in large numbers. Modern
giant tortoises from the granitic Seychelles can have a diversity of shapes (Bour,
1984c), which has led some to treat them as separate species (Gerlach and Canning,
1998), but molecular evidence shows them to be identical or virtually identical to
each other and to Aldabran tortoises (Austin et al., 2003; Palkovacs et al., 2003;
Karanth et al., 2005). In the absence of DNA evidence from subfossil specimens
that unequivocally pre-date human settlement, it remains unknown whether the
species that is now restricted to Aldabra naturally occupied the granitic islands or
whether those islands contained only extinct endemic species. So, it remains uncer-
tain whether the numerous introductions of Aldabran tortoises to the granitic
Seychelles represent instances of reintroduction of a native species or introduction
of an alien, although I have conservatively treated them herein as the latter.
It is clear from these examples that loss or muddling of taxonomic or distribu-
tional knowledge can have practical ramifications for conservation above and
beyond merely reducing the total fund of human knowledge. Another example is
provided by the pool frog,
Rana lessonae
, known to be introduced into Great
Britain several times since the mid-1700s. It has long been thought that all popula-
tions within Great Britain originated from such introductions, but recent evidence
