Introduction Patterns - Alien Reptiles and Amphibians - page 29

It is against this overall exponential increase in alien herp introductions that the
following analyses elaborate.

Taxonomic Variation

Introduction and success rates vary considerably among taxa and can be tracked in
two different ways. For those data that admit of time-series analysis, frogs have
been introduced most frequently, followed by lizards, turtles, and snakes, with sala-
manders and crocodilians relatively rarely introduced (Fig. 2.2). For each of these
taxa, with the exception of crocodilians, growth in introduction rate is exponential,
although rates, and therefore doubling times, differ (Table 2.1). Crocodilians have
been infrequently introduced and growth in their numbers with time is largely

Table 2.1 Growth rates for herpetological taxa
Taxon Growth type Growth equation R 2 Doubling time (years)

Frogs Exponential y = 17.396e 0.2310x 0.9934 29.9

Salamanders Exponential y = 0.63.47e 0.3142x 0.9746 22.0

Lizards Exponential y = 9.3101e 0.2424x 0.9820 28.5

Snakes Exponential y = 4.7193e 0.2368x 0.9548 29.1

Turtles Exponential y = 4.7072e 0.2763x 0.9843 25.0

Crocodilians Linear y = 3.5667x - 5.5 0.9760 NA

All taxa Exponential y = 43.600e 0.2532x 0.9978 27.2

Fig. 2.2 Cumulative growth in reptile and amphibian introductions by taxon. Frogs = dark blue,
salamanders = green, lizards = yellow, snakes = blue, turtles = pink, and crocodilians = red