Biology Reference
In-Depth Information
2.
Adaptation of Alien Species
for Dispersal and Establishment
“Founding events provide one circumstance in which rapid changes in the
external and internal (genetic) environment might occur.These events pro-
vide a possible escape from the homogenizing effects of large populations, or
perhaps alter the balance of advantages in pleiotropic genes such that one of
the characters they control is no longer disadvantageous. . .”
—G
RAY
(1986)
From 1981 to 1991, Martin Cody and Jacob Overton (1996) censused
vascular plants on small islands in Barkley Sound on the west coast of
Vancouver Island, British Columbia, Canada. These censuses revealed
many cases of colonization and extinction. Colonization by most species
resulted from seeds that were adapted for wind dispersal and were blown
from mainland areas. This raised several interesting questions. First, were
the seeds that reached the islands different from those that did not? Sec-
ond, were the seeds of plants that maintained populations on the islands
different from those of mainland plants? Third, did seed structure change
through time for plants that maintained populations on the islands? For
three species of wind-dispersed annual or biennial herbs of the aster fam-
ily, Cody and Overton were able to compare seed morphology for pop-
ulations on island and mainland areas, and, for two of the three, for islands
varying in the length of time since colonization.
One species, woodland ragwort (
Senecio sylvaticus
), showed no differ-
ences between mainland and island areas, but the other two did. For one
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