Biology Reference
In-Depth Information
Chapter 2
Introduction Patterns
What is the magnitude of alien herpetofaunal dispersal by humans? How are
these species being dispersed by humans? Is it mainly the result of intentional
actions liable to easy personal control, or an accidental phenomenon of human
actions having statistically probable outcomes? Have the mechanisms of intro-
duction been stable through time or varied? Are the same mechanisms important
everywhere, or do pathways differ in importance geographically? How success-
ful are alien reptiles and amphibians at establishing populations in the new
regions to which they have been transported, and what factors might explain
this success?
These are the very basic questions that need to be answered if the phenomenon
of reptile and amphibian invasion and its dependence on human behavior are to be
understood. A quantitative analysis of these questions is typically referred to as a
“pathway analysis” because it assesses the details of how and why species are
transported by humans. A pathway analysis is a prerequisite for any informed
managerial response to herpetofaunal invasions because it provides the data needed
to meaningfully intervene in the first step of that process. Once pathways are identi-
fied and their variation clarified, one may then investigate predictive factors (e.g.,
ecological, economic) that might explain pathway strength and establishment success.
This knowledge may then be applied to design measures to restrict pathway
strength and success.
Such analysis has historically been hindered for reptiles and amphibians because
the requisite literature and evidence remained uncollated. The only prior attempt I
know to provide a pathway analysis for reptiles and amphibians is my earlier study
(Kraus, 2003c) that was based on approximately one-tenth of the records in the
current database. That study was a sampling of those records that I could find in a
period of two months and it was acknowledged as suffering from at least a geo-
graphical bias. The current database is a sufficiently complete sampling of the
literature that it more closely approximates a census of available global information.
Hence, I think the limitation of geographic sampling bias present in the earlier
study no longer applies to any serious extent.
The database and details on its interpretation are provided in Appendix A. I have
used 1850 as a convenient point at which to begin the analyses below because few
records reporting introductions precede that date; however, the database includes
