Environmental Engineering Reference
In-Depth Information
Nonnative species
(synonyms: alien,
exotic, foreign,
nonindigenous)
Species present in a region beyond their historic range.
Propagule pressure
The quantity or rate of nonnative organisms released into
an area.
Definition of the Subject
Biological invasion is the process by which a species is introduced, deliberately or
inadvertently, into a new geographic region where it proliferates and persists.
Outside their historic range (in which they evolved) such species are described as
nonnative (or nonindigenous, exotic, alien). For a variety of reasons, the vast
majority of introduced nonnative organisms fail to persist. Many of those that do
establish self-sustaining populations do not spread very far or very fast beyond their
point of introduction, and they often do not have conspicuous impacts on their
environment. However, a small proportion (but a large and growing number) of
nonnative species becomes invasive - that is, they may spread aggressively and/or
have strong environmental effects. Invasive species are a global problem that
threatens native biodiversity, the normal functioning of ecosystems, natural
resources, regional economies, and human health. As such, they pose a major
concern for conservation and management, and are the focus of a highly productive
multidisciplinary field called invasion ecology .
Introduction
The potential impact of nonnative species has long been recognized by naturalists.
In The Origin of Species , Darwin (1859) warned “Let it be remembered how
powerful the influence of a single introduced tree or mammal has been shown to
be [on native communities].” A century later, Charles Elton's groundbreaking
monograph The Ecology of Invasions by Animals and Plants [ 1 ] helped inspire
two generations of scientists to study what has become one of the world's most
challenging environmental problems.
The major findings of this burgeoning research are summarized in recent texts by
Lockwood et al. [ 2 ], Davis [ 3 ], Blackburn et al. [ 4 ], and Richardson [ 5 ].
This entry describes the causes and consequences of biological invasions, by
synthesizing concepts from population biology, community ecology, evolution,
biogeography, and conservation biology. First, the patterns and process of invasion
are explored; then, some of its potential ecological and socioeconomic impacts are
examined. Some major hypotheses and theoretical concepts explaining patterns of
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