Biology Reference
In-Depth Information
and Nötzold compared plants of purple loosestrife (
Lythrum salicaria
) from
their native range in Europe with plants taken from invading populations
in North America.These plants were grown in a common garden in New
York State.The North American plants grew substantially taller and pro-
duced much greater biomass than the European plants. Furthermore, tests
with a root-feeding beetle (
Hylobius transversovittatus
) showed that its sur-
vival was more than three times as great on the North American plants as
on the European plants, suggesting that some defense against this insect
had become weakened.
Invasive forms of the Chinese tallow tree (
Sapium sebiferum
) in
Louisiana and Texas appear to be a recently evolved ecotype with foliage
that has reduced chemical defenses against herbivores (Siemann and
Rogers 2001). Chinese tallow trees in North America do not yet appear
to have accumulated a significant fauna of herbivores. Thus, even with
reduced defenses, they are able to grow larger and produce more seeds
than the original Asian ecotype introduced to the southeastern United
States (Rogers and Siemann 2002).
The occurrence of trade-offs between growth or reproduction and
herbivore defenses in plants such as purple loosestrife and Chinese tallow
tree is thought to be frequent among invasive alien species. As Siemens et
al. (2002) pointed out for field mustard (
Brassica rapa
), however, chemicals
that defend against herbivores may have other functions that remain active
in the alien environment. In addition, Koricheva (2002), through a meta-
analysis of studies that have measured fitness costs of anti-herbivore
defenses, showed that such defenses are part of a complex adaptive syn-
drome and are not easily evaluated by short-term measurements.
Although many of the studies Koricheva examined did not involve alien
plants, her analysis showed that adaptive trade-offs may not always be
obvious for plants introduced to new biotic contexts.
Introduction of animals to new regions can also lead to rapid evolu-
tionary adjustment to new biotic conditions, particularly the predation
regime.Tammar wallabies (
Macropus eugenii
) were originally widespread in
mainland Australia, where they were adapted to a variety of large preda-
tors.They were introduced to predator-free Kawau Island, in the Haruaki
Gulf, North Island, New Zealand, in the 1870s. From there, they were
introduced to the mainland of the North Island, near Rotorua, in 1917.
Thus, these animals have lived free of large predators for more than 130
yr. Blumstein (2002) tested the behavioral responses of Rotorua wallabies
to visual and acoustic stimuli of large predators. He found that they
showed reduced recognition of all but the large marsupial wolf (
Thylaci-
