Environmental Engineering Reference
In-Depth Information
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Fig. 10.2 Prehistoric versus modern rates of invasion (number of nonnative species established
per year) for various regions. Prehistoric rates (grey bars) are before human settlement and were
estimated from the fossil record or by calculating numbers of “native” species (excluding
endemics) that have become established in the region over time. Modern rates (black bars) are
inferred from discovery rates averaged over the past 40-100 years (Modified from [ 58 ])
few centuries, coinciding with steep increases in global trade, human travel, and land
use. Invaders are presently colonizing new regions at rates that are several orders of
magnitude faster than prior to human arrival ( Fig. 10.2 ). Even the seemingly remote
Antarctic continent and its surrounding islands have been colonized by nearly 200
nonnative species of terrestrial plants, invertebrates, and vertebrates within the past
two centuries, owing to the effects of scientific exploration, increased accessibility
by air and by sea, a burgeoning tourist industry (tens of thousands of visitors
annually), and a changing climate [ 59 ]. The modern rate and geographic extent of
invasion is without historical precedent [ 58 ].
Ecological Impacts
Most nonnative species appear to have only minor effects on their invaded systems,
but this observation is tempered by two caveats: The impacts of the vast majority of
invasions have not been studied [ 60 ], and even species that are generally benign can
become disruptive at different times or different locations [ 61 ]. In many cases,
 
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