Biology Reference
In-Depth Information
quinquenervia
), Brazilian pepper (
Schinus terebinthefolius
), and others have
established woodland communities in areas of former coastal strand and
marsh in Florida. Along the Gulf Coast of the United States, Chinese tal-
low (
Sapium sebiferum
) is converting coastal prairie to alien woodland
(Bruce et al. 1995). Riparian woodlands in the western United States have
been transformed by invasions of salt cedars (
Tamarix
spp.), Russian olive
(
Eleagnus angustifolia
), and several other alien trees that are gradually dis-
placing native trees and shrubs. Intermontane grasslands and shrub steppes
of the western United States and Canada are being invaded or almost
completely displaced by annual brome grasses (
Bromus
spp.) and broad-
leaved herbaceous knapweeds and starthistles (
Centaurea
spp.). Alien
annual and perennial grasses are invading warm deserts, where they are
introducing fire to vegetation types that rarely burned. Native strand
communities of the Pacific coast are becoming dominated by European
beachgrass (
Aimophila arenaria
).
Elsewhere in the world, similar community transformations also are
occurring, as we saw in the example opening this chapter. Many other
examples can be cited. In Australia, Monterey pine (
Pinus radiata
) is invad-
ing native eucalyptus woodland from adjacent pine plantations (Burdon
and Chilvers 1977). Australian eucalypts (
Eucalyptus
spp.) have become
established in many locations around the world, creating woodland com-
munities in former grasslands and shrublands. North American and Euro-
pean pines (
Pinus
spp.) and Australian acacias (
Acacia
spp.) and needle-
bushes (
Hakea
spp.) are threatening the fynbos shrublands of South Africa.
Aquatic ecosystems, both freshwater and marine, are being altered as
well. Deliberate and accidental introduction of nonindigenous species,
especially fish and molluscs, is one of the major threats to native biodiver-
sity in freshwater lakes (Lodge 2001). The North American Great Lakes,
for example, are now home to more than 139 alien plants and animals.
The Baltic Sea is now home to 100 or more alien species, derived from
all continents except Antarctica (Leppäkoski and Olenin 2001; Lep-
päkoski et al. 2002). In Pearl Harbor, Hawaii, alien species dominate the
biota (Englund 2002). A recent survey documented 191 alien aquatic
species derived from all parts of the world.
Not only is the composition of these biotic communities altered, the
pattern of ecosystem function is transformed as well.Thus, native species
are not only faced with new biotic challenges of competition, predation,
and disease, but also with changes in physical and chemical conditions,
resource availabilities, and disturbance regimes.The evolutionary stage for
both native and alien species has been largely rebuilt.
