Biology Reference
In-Depth Information
ecosystem values and of the anchovy fishery (Kideys, 2002).
Mnemiopsis leidyi
has
subsequently been introduced into the Caspian Sea as well, and can be found there
in plague proportions at densities >2,000/m
2
. Similar ecological and economic
damage followed: fisheries losses to Iran alone have exceeded US$125 million
(Kideys, 2002; Stone, 2005). Unfortunately, the salinity of the Caspian Sea is insuf-
ficient to support healthy populations of
Beroe
, thus the control of
M. leidyi
happily
effected in the Black Sea looks unlikely to succeed in the second case.
It is hard to decide with this example which has a stronger grip on the imagina-
tion: the novelty or the horror of an obscure invertebrate decimating the Black Sea
and Caspian Sea ecosystems. This example is especially instructive because at the
time of ballast-water discharge, no one would have predicted that the “mere” comb
jelly thus released would lead to such devastating impacts within a few years.
A similar unpredictable scenario applied to the introduction of brown treesnakes,
Boiga irregularis
, to Guam. The literature is replete with similar examples where
the ecological damage attending an introduction would have been equally impossible
to predict. In other cases, negative impacts were perfectly predictable but ignored
until too late, such as with the introduction of coqui frogs (
Eleutherodactylus coqui
)
to Hawaii or predatory snails (
Euglandina rosea
) and flatworms (
Platydemus
manokwari
) around the islands of the Pacific.
Despite an abundance of impacts on humans and their economic activities, eco-
nomic costs from invasive species have only infrequently been measured, except for
some agricultural pests. Economic costs include those resulting from damage, con-
trol, research, defensive prevention, and foregone economic opportunities that
attend the irreversibility of pest invasions, which is especially difficult to measure
(Perrings et al., 2005). Even when economic impacts are recognized, monetary
estimates are usually lacking. However, this is beginning to change, and even con-
servative estimates have found the monetary costs of invasive species to be staggering.
As one example, Pimentel et al. (2005) conservatively estimated the total cost of
invasive species to the economy of the United States to exceed US$120 billion/year.
Proportionately similar costs no doubt apply to many other economies. Such esti-
mates (see Pimentel, 2002; McNeely, 2005; Perrings et al., 2000, 2005; Pimentel
et al., 2000, 2005) rarely involve reptiles or amphibians, but what data are available
for those taxa are presented in Chapter 3.
The impacts discussed above and emphasized in the literature are all of prac-
tical concern to one degree or another, affecting humans directly or affecting the
ecosystems that support us and innumerable other species. There is one more
impact that I wish to mention that is of less obvious practical import and is virtu-
ally ignored in the literature on alien species. This is loss of beauty. That such
an aesthetic impact exists might seem counterintuitive inasmuch as introductions
via the pet trade and deliberate introductions due to personal fondness for an
animal's appearance are so frequent (see Chapter 2). After all, an assortment of
lizards, birds, and many other species are lovely, widely kept as pets, and some-
times released for that reason. How could introductions motivated by an appre-
ciation for these animals' beauty lead to loss of beauty? Does this not present us
with a paradox?
