Biology Reference
In-Depth Information
8.
Adaptation of Alien Species
to New Habitats
“Founder effects, genetic drift, and natural selection can all lead to genetic
differentiation in populations of an invading species, relative to the invader's
source population.”
—D
AEHLER AND
S
TRONG
(1997b)
In about 1894, smooth cordgrass (
Spartina alterniflora
) was accidentally
introduced to Willapa Bay, Washington, apparently becoming established
as a single clone. In a little over a century, the species has spread over more
than 1,000 ha, partly through vegetative spread and partly by reproduc-
tion by seed. Smooth cordgrass is native to the Atlantic coast of North
America, where it has a specialist herbivore, the planthopper
Prokelisia
marginata
(Order Homoptera).
Prokelesia
is absent from Willapa Bay, but
occurs in populations of smooth cordgrass that were introduced into San
Francisco Bay in the 1970s.
Daehler and Strong (1997b) examined the susceptibility of smooth
cordgrass from Willapa Bay, San Francisco Bay, and Chesapeake Bay,
Maryland, to herbivory by
Prokelesia
over two growing seasons in a
greenhouse. They also examined the preference of
Prokelesia
for plants
from these three populations. Cordgrasses from San Francisco Bay and
Chesapeake Bay showed little or no reduction in biomass production
compared to plants protected from herbivory. The Willapa Bay plants,
under experimental herbivory by
Prokelesia
, showed an 88% average
reduction in biomass production by the second greenhouse growing
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