Environmental Engineering Reference
In-Depth Information
graphic ranges (Mack et al. 2000). Such biotic invasions occur when organ-
isms are transported to new, often distant ranges where their descendants
proliferate, spread, and persist. Such invasions are cause for significant con-
cern in the conservation of ecosystems and endemic biodiversity within
them. Invading species can alter fundamental ecological properties such as
the dominant species in an ecosystem, and the biophysical features of
ecosystems, including nutrient cycling and plant productivity (Mack et al.
2000).
In the game of life, invasive species are, on average, better at utilizing the
same set of resources as those used by a native species or they are better at
translating those resources into fitness because they have fewer costs in their
new geographic locations owing to release from biotic constraints. For ex-
ample, predators might not recognize a novel invader as a potential prey
item, thereby freeing the invasive species from the need to devote time or
energy to avoid predators. In this case, the invasive species is less intercon-
nected to other species than are the native species with which it competes.
In other cases, the invasive species may be a novel, voracious predator that
devastates native species that have not evolved the capacity to deal with this
new predator species.
Invasive species often affect eco-
systems by wedging themselves into
them and then systematically causing
the collapse of the entire system. A
classic example of such an effect in-
volves the Zebra mussel ( Dreissena
polymorpha ).This species is native to
the Caspian Sea region of Asia and
was transported to the U.S. Great
Lakes in ballast water in a cargo ship
(Ricciardi and MacIsaac 2000). The
ballast water was discharged before
the ship entered port in Detroit. Adult female zebra mussels, which are no
bigger than your thumbnail, can produce between thirty thousand and one
hundred thousand eggs per year. Zebra mussels invade aquatic food webs by
attaching to fixed surfaces.They then outcompete native species by rapidly
filtering phytoplankton from the water column.The loss of the phytoplank-
ton base has reverberated upwards in the ecosystems through loss of zoo-
plankton and fish species in higher trophic levels. In addition, Zebra mussels
In the game of life, invasive species
are, on average, better at utilizing
the same set of resources as those
used by a native species or they are
better at translating those
resources into fitness because they
have fewer costs in their new geo-
graphic locations owing to release
from biotic constraints.
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