Impacts of Alien Reptiles and Amphibians
The entire motivation for concerning ourselves with invasive alien species, of course, relates to the ecological and economic damage these species cause. For many non-herpetological taxa, as noted in Chapter 1, damages have been extensive and severe, justifying the considerable attention that has been devoted to a host of invasive pests of all groups. As for these better-known taxa, when determining the degree of attention that alien reptiles and amphibians might merit as a management problem it is imperative to assess to what extent these species inflict damage. Clearly, if these animals are not affecting natural or human ecosystems, concern for their introduction will be lessened. And, indeed, it has been argued that most reptile and amphibian introductions to Florida provide no such impact, and the threat of alien herpetofauna there has been largely discounted (L.D. Wilson and Porras, 1983; Butterfield et al., 1997). Alternatively, if it be shown that alien reptiles and amphibians do cause an array of ecological or societal damages, a greater responsi bility for management response would inhere. In either event, a broader awareness of these impacts or their absence would improve our assessment of the relative standing of alien reptiles and amphibians as environmental, conservation, or social problems. It would concomitantly serve to identify obvious research needs for fur ther clarifying extent and ecological mechanisms of impact as well as control and mitigation measures.
A broad survey of ecological impacts attending invasive reptile and amphibian introductions has not previously been available. In providing one here, I confine my attention to studies that clearly demonstrate some level of impact from alien her-petofauna and that provide some evidence or compelling argument as to what the mechanism of such impact might be. In including instances that provide only reasoned argument to identify impact mechanism I hope to highlight several hypotheses that have languished in the literature for lack of further investigation. The literature occasionally contains correlational evidence that simply notes the decline or disap pearance of a native species to be coincidental with expansion of a naturalized alien (e.g., Münch, 2001). However, such correlations need not result from the intro duced alien per se; both species may simply be responding differently to underlying environmental changes (cf. L.D. Wilson and Porras, 1983 for herpetological examples). Such instances are generally omitted in this summary because evi dence identifying the causative mechanism of replacement is not provided. Nonetheless, such correlational evidence points to additional potential instances of detrimental impacts that may warrant investigation. Lastly, concerns have fre quently been expressed in the literature for a variety of potential impacts for which no evidence is provided whatsoever. Some of these speculations may be valid, but in the absence of documentary evidence or reasoned argument they do not approach minimal scientific standards and are ignored here.
KeywordsBiomass Depression Europe Holocene Fishing
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