Biology Reference
In-Depth Information
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.
This survey reveals that a surprisingly wide array of deleterious impacts are docu-
mented across a variety of herpetological species, even though taxonomic sampling
among naturalized herpetofauna has been sparse. Indeed, research into impacts from
alien reptiles and amphibians is rather recent, and it is to be expected that additional
examples and further impacts will be identified as research into this area garners
greater momentum. Impacts identified to date may be broadly categorized as eco-
logical, evolutionary, or social. The first includes impacts on individual species as
well as broader community-level disruptions. Ecological damages from alien her-
petofauna most often derive from food-web disruptions, with impacts stemming
from predation on sensitive species, poisoning of predators, competition with
natives, vectoring of novel parasites, or secondary disruption of food webs.
Evolutionary impacts encompass genetic contamination via hybridization with
natives as well as changes in inherited morphological, physiological, or behavio-
ral traits. Genetic impacts relate to introgression of alien genes into native gene
pools, sometimes to the point of genetically swamping native forms out of exist-
ence. Under the category of evolutionary change are included both changes
observed in the invasive alien as well as modifications induced in native fauna by
its introduction. Social damages include direct impacts on humans or their cul-
tural institutions. These impacts can be to human health, economies, quality of
life, or scientific knowledge.
Ecological Effects
Removal of Native Prey Species
The most widely studied and commonly considered ecological effect from alien
reptiles and amphibians is predation on sensitive native species resulting from the
introduction of novel predators. In only a few instances has direct evidence of popu-
lation-level effects on natives been demonstrated, but many anecdotal observations
suggest it may be a frequent phenomenon. This is, however, difficult to document
because intense, novel predation may provide only a narrow window of opportunity
for observing populations during the phase of decline. More often, sudden rarity is
noticed after the fact and the cause can only be inferred retrospectively by temporal
correlation with a newly introduced predator.
The best-known instance of predation leading to loss of native species is the
introduction of the brown treesnake (
Boiga irregularis
) to Guam in the years
