Invasive species are non-native plant and animal species
(also called "exotics") that have moved into
an ecosystem and displaced the original wildlife that
was found there.
Exotic plants, such as purple loosestrife, have crowded
out native wildlife in wetlands and other habitats at
more than half of Canadas National Wildlife Areas
and Migratory Bird Sanctuaries. Similarly exotic animal
species threaten native species by increasing the likelihood
of competition and predation, and by destroying critical
are four examples of problematic invasive species.
Large populations of carp introduced into the Lake St.
Clair National Wildlife Area have damaged beds of native
vegetation, and their spawning activities have destroyed
the nests and eggs of many bird species in area marshes.
Scientists suspect the explosive spread of zebra mussels
in the Great Lakes is altering the food chain, changing
water chemistry and physically disabling native species.
The direct economic impact is estimated at more than
three billion dollars.
salamander, Gary M. Stolz/USFAWS
Vaseux-Bighorn National Wildlife Area in British Columbia
is considered one of the most threatened in western
Canada. Many of its native grassland species, such as
bluebunch wheatgrass and cheat grass, are being crowded
out by exotic plant species like smooth brome grass.
The areas wildlife, including the threatened pallid
bat and the endangered tiger salamander, is dependent
upon the native grasslands for cover and hunting grounds.
Purple loosestrife is crowding out native wildlife and
reducing biodiversity in wetlands at 19 National Wildlife
Areas and Migratory Bird Sanctuaries, mostly in eastern
Canada. It is also one of nine invasive species displacing
native wildlife at Lac Saint-FranÁois National
Wildlife Area in Quebec.