Biology Reference
In-Depth Information
Rana ridibunda
is obfuscated by recent introductions of allochthonous frogs
(Pagano et al., 2003). Paleontological (Alcover and Mayol, 1981) and some bio-
chemical evidence (Hemmer and Kadel, 1980; Hemmer et al., 1981) suggests that
few species of reptiles and amphibians occurred on the Balearic Islands until
human occupancy and that most of the current herpetofauna there is introduced.
Similar results may obtain elsewhere on Mediterranean islands (e.g., Böhme and
Wiedl, 1994; Corti et al., 1999; Pascal et al., 2006; but see Vigne et al., 1997 for a
counter-example) but have not yet been conclusively demonstrated. In Madagascar,
the few species shared with mainland Africa have sometimes been suspected to be
introductions; for example,
Kinixys belliana
is argued to be an ancient introduction
(Bour, 1978, 1987, 2006). However, Madagascan
Ptychadena mascareniensis
-
another species shared with mainland Africa - has recently been shown to be native
(Vences et al., 2004a), and
Kinixys
merits similar testing. The lizard
Zonosaurus
madagascariensis
on Aldabra and Curieuse in the Seychelles is variously argued to
be introduced (Henkel and Schmidt, 1995) or native (Matyot, 2003). The partheno-
genic blind snake
Ramphotyphlops braminus
now has a virtually pan-tropical dis-
tribution, most likely having travelled with humans for millenia. It's origin is
unknown but is likely to be southern Asia, where its presumed closest relatives live
(A. Wynn, United States National Museum, personal communication, 2006).
Conversely, the obvious fact that herpetological species are transported by
humans has led to a number of uncritical claims for human introduction that have
no direct or compelling inferential evidence. For example, C. Lever (2003) asserted
without evidence that a variety of lizards native to islands of the central Pacific are
alien (see Appendix B). Brown and Alcala (1970) provided a list of 23 reptiles and
amphibians that they asserted were non-native to the Philippines, and Iskandar and
Tjan (1996) did the same for 19 species of reptiles and amphibians on Sulawesi, an
assertion repeated by Inger and Voris (2001). But these claims were based solely on
distributional evidence and ability to thrive in human-disturbed habitats (Brown
and Alcala) or distributional impressions on an imperfectly studied island (Iskandar
and Tjan). In the latter case, the authors acknowledged that some of their records
could be nothing more than cases of mistaken provenance. Prior belief that the
endemic
Indotestudo forstenii
of Sulawesi was also a human introduction (Pritchard,
1979; Groombridge, 1982; Hoogmoed and Crumly, 1984; Iskandar, 2000) has been
shown to be false (Iverson et al., 2001), so such assertions should be viewed (and
made) with caution. Nonetheless, these claims, though not yet compelling, do high-
light the potentially significant complement of cryptogenic species within a wide
array of insular herpetofaunas. Some of these hypotheses of human-mediated
origins are potentially testable by investigation of patterns of genetic variation, but
that need not always be the case, and some cryptogenic species will undoubtedly
remain lost to scientific understanding.
Taxonomic clarity too can suffer from alien reptile introductions, as indicated by
the case of
Anolis distichus
in Florida discussed earlier. In that instance, taxonomic
distinctiveness of a possibly native lineage was obliterated by genetic introgression
of foreign genomes, and it is now likely impossible to determine whether
A. d. floridanus
was truly a native Floridian element or an older introduction. Turtles provide
