Biology Reference
In-Depth Information
percentages of leaf-miners were 14.4 for sawtooth oak and 26.8 for Japan-
ese chestnut.This suggested that the introduced trees were very favorable
hosts for some of the miners. Thus, both alien trees had acquired a rich
fauna of leaf-mining insects in only 13-14 yr.The species with close rel-
atives in nearby forests, the sawtooth oak, appeared to have gained more
leaf-miners than the Japanese chestnut, which lacked nearby congeners.
Some combination of nutritional factors, together with parasitism and
predation patterns, seemed to be responsible for the greater overall emer-
gence success of leaf miners on the alien trees.
This study (Auerbach and Simberloff 1988) showed that colonization
of newly introduced plants by herbivorous arthropods can be very fast and
that the taxonomic similarity of new plant species to natives is an influ-
ential factor in this colonization process. Furthermore, it appeared that the
physiological condition of successful plant colonists might facilitate the
success of some of these arthropods.
Biotic Responses to Alien Species
As we saw in chapter 7, newly colonizing alien plants and animals are
often free of many of the enemies that attack them in their native region.
For at least some species, this release is a major factor in their becoming
highly invasive.Very few aliens, however, remain free from attack by native
herbivores, predators, or parasites for very long.The pattern of interaction
that develops between alien species and these new enemies can lead to
patterns of rapid evolution in both alien and native species, as we have also
seen. The potential for such evolution depends on the number of native
colonists and the speed with which they begin to colonize and interact
with aliens.
Factors Influencing Accumulation of Species by
Alien Plants
In almost all cases, introduced plants sooner or later become the object of
exploitation by native herbivores and parasites. Acquisition of such ene-
mies tends to follow an asymptotic curve, being rapid at first and slowing
as an equilibrium relationship is approached (Bernays and Graham 1988).
Generalist species are the first to use new aliens, with their diversity
reaching a plateau in as little as 100 yr. Colonization of new aliens by
feeding specialists, on the other hand, may take as much as 10,000 yr.
The pattern of accumulation differs for various kinds of aliens and is
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