Biology Reference
In-Depth Information
uninformed public to accept, sometimes leading to unnecessary opposition to
alien-species control programs needed to prevent extinctions of native species. I am
unaware of any studies to quantify the effects of this particular form of social ignorance
upon policy or managerial decisions, but the impression for many actively involved in
management of invasive species is that it often leads to significant problems.
Conclusions
As the survey above indicates, a wide variety of negative impacts has been shown
to attend the introduction of alien reptiles and amphibians - impacts that mirror
many of those seen in better-studied groups like mammals. Despite this diversity, it
is important to note that only a small subset of naturalized species or populations
has received any form of impact study. Hence, while at least 322 species of reptiles
and amphibians have been naturalized across the globe, only 14 species have had
ecological impacts demonstrated or reasonably inferred (Table 3.2). Of these, only
three species ( Boiga irregularis , Bufo marinus , and Rana catesbeiana ) could be
said to be even moderately well studied; most of the remainder have had impacts
demonstrated in only one or a few studies of limited scope. Similarly, evolutionary
impacts have been demonstrated or implied for 17 species. Most of these involve
instances of hybridization with native relatives. Although not all instances of
hybridization have been demonstrated to have importance at the population level,
several clearly do. Lastly, economic or health impacts on humans have been demon-
strated (n = 4) or implied but not compellingly proven (n = 2) for six species. In
total, excluding instances of epistemological loss of knowledge, which are currently
too numerous and uncertain to quantify, 26 species of reptiles and amphibians are
demonstrated to have caused or are credibly implicated in ecological, evolutionary,
economic, or health effects on native wildlife or humans (Table 3.2).
It could be argued that this small number reflects the fact that alien reptiles and
amphibians are largely innocuous and warrant ignoring. That is possible, but it is
neither a scientifically cautious nor compelling interpretation. More likely, this
modest number reflects widespread inattention to impact phenomena among rep-
tiles and amphibians and the difficulty of convincingly demonstrating them.
Consistent with that interpretation is that the large majority of articles cited above
have been published in the past 20 years and that such studies are dramatically
increasing in frequency (Fig. 3.1). Most of the earlier studies recorded in Fig. 3.1
are merely anecdotal references; experimental studies didn't begin until the 1970s.
Further, the species demonstrably or likely causing impacts for which dates of
introduction can be estimated (this excludes several more ancient introductions of
undetermined age) were introduced from 20-175 years ago, with an average
introduction date of 62 years ago. Since approximately two-thirds of all herpetofaunal
introductions have occurred in the past 60 years, the lag in scientific study alone
suggests that a considerably larger pool of impacts will eventually emerge. This
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