Introduction Patterns - Alien Reptiles and Amphibians - page 30

linear. Although frogs and lizards have been introduced most often, the actual rate
of increase in introductions through time has been highest for turtles and salamanders
(Table 2.1), even though those taxa have not been introduced as often.
Alternatively, instead of restricting analysis to those introductions of approxi-
mately known dates, the sum total of all introductions can be examined for each
taxon. Doing so indicates turtles to have been introduced far more frequently than
any other taxon (Fig. 2.3). However, this total is heavily influenced by the wide-
spread introduction of the common pet turtle Trachemys scripta . If this species is
removed from the analysis, then numbers of turtle introductions are more in line
with those for other taxa (Fig. 2.4). In either event, rates of successful establishment
differ among taxa (Figs. 2.3-2.5), with lizards having the highest rate, followed by
frogs, salamanders, and snakes. Turtles and crocodilians have very poor overall rates
of establishment. If relative establishment success of turtles is calculated excluding
T. scripta , establishment success rates (Fig. 2.5) increase from 5.7% to 7.7% only.
Most species have only single records of introduction, with the number of spe-
cies having larger numbers of introductions declining as a negative power function
(y = 419.44x −1.8280 , R 2 = 0.9077, Fig. 2.6). Nonetheless, 87 species of reptiles and
amphibians have been subject to more than ten introductions each, with Trachemys
scripta again being the most widely released species, with 1,430 records.
Numbers of introductions per family vary in a similar fashion, with 34 families
having been introduced more than ten times and 11 families introduced more than
100 times (Table 2.2). The distribution of numbers of introductions among these
families also approximates a negative power function (y = 6331.5x −1.8406 , R 2 =
0.8572). The fit of this equation to the data is compromised by the large number of
families having only a few introductions. Restricting attention to only those families
Fig. 2.3 Differences in numbers of introductions among reptile and amphibian taxa. Solid bars
are data for all introductions, open bars for successfully established introductions, where estab-
lishment is counted only once per jurisdiction