Invasive Species - Ecological Systems - page 168

40% of all harmful weeds, 30% of arthropod pests, and 70% of plant pathogens, and
cause substantial losses in total crop production each year [ 85 ]. A single invasive
forest insect, the emerald ash borer beetle, is projected to cost the United States $10
billion over the next decade [ 86 ]. The 2001 outbreak of foot-and-mouth disease in
the United Kingdom, linked to illegal meat imports, cost $25 million USD and
required the slaughter of 11 million animals [ 87 ]. The annual costs of 16 nonna-

tive species to fisheries, agriculture, and forestry in Canada are projected to be as
high as $34 billion CDN [ 88 ]. The combined annual costs of biological invasions in
the United States, United Kingdom, Australia, India, South Africa, and Brazil are
estimated to be $314 billion USD. Assuming similar costs worldwide, the global
economic damage attributable to invasions amounts to US $1.4 trillion per year,
which constitutes 5% of the global economy [ 85 ].
Whereas some nonnative species perform valuable roles, other nonnatives can
degrade ecosystem services - including water purification, soil stabilization, agri-
cultural yield, disease regulation, and climate regulation [ 89 ]. The conservation of
water resources in African countries is threatened by introduced plants [ 90 ],
whereas pollination services provided by European honeybees are threatened by
Asian Varroa mites, whose parasitism has destroyed entire hives [ 91 ]. Animal
(including human) health, in general, is threatened by invasions that spread
parasites, diseases, and their vectors (e.g., mosquitoes [ 92 ]). Invasions can also
alter the transmission of parasites to humans by introducing hosts to novel regions
[ 93 ]. About 100 species (

6%) of nonnative invertebrates (e.g., spiders,
mosquitoes, nematodes) in Europe adversely affect human or animal health, and
these are a subset of 1,300 nonnative species in the region that have documented

socioeconomic impacts [ 94 ]. Climate change is expected to drive a new wave of
such invasions, as suggested by the recent occurrence in Northern Europe of the
tropical virus that causes “bluetongue disease” that resulted from the introduction
of infected livestock from a Mediterranean country [ 95 ].

Management of Invasions

Risk Assessment

Managers have few tools for prioritizing invasion threats because reliable predic-
tive methods are scarce (but see [ 96 , 97 ]). Progress in developing a predictive
understanding of impact has been hampered by the lack of standardized metrics.
Parker et al. [ 60 ] proposed a metric for impact (I) that can be compared across
species and invaded sites:

I R A E

¼

where R is the total area occupied by the nonnative species in its invaded range, A is
its abundance (in numbers or biomass per square meters) in the invaded range, and
E is its per-capita effect based on the functional ecology and behavior of individuals