Biology Reference
In-Depth Information
the British Isles. Schluter (2000) summarized information on character
displacement for a large number of birds and mammals and a few inver-
tebrates.
In addition to character displacement, predators introduced to new
areas may encounter a new spectrum of prey sizes, regardless of whether
or nor they have been released from pressure of competitors. Selection
may thus favor adjustments of body size or feeding apparatus appropriate
to the new range of prey sizes.
Evolutionary Adaptation by Invertebrate Predators
and Animal Disease Vectors
Many parasitoid insects have been introduced to North America and
other world regions, in almost all cases as potential biological control
agents. The target pests themselves are usually alien species. Many intro-
duced parasitoids, however, extend their feeding activity to native species.
In Hawaii, for example, more than 32% of 115 parasitoids introduced for
biological control have begun to attack hosts other than the target pest.
In mainland North America, about 16.3 % of 313 introduced parasitoids
have been recorded from native, nontarget species (Hawkins and Marino
1997). At least one parasitoid wasp has shown evolutionary adaptation to
conditions of crop and noncrop habitats in which its prey occurs (see
chapter 17). Other parasitoid wasps, such as
Aphidius ervi
, which attacks
pea aphids (
Acyrthosiphon pisum
) in clover and alfalfa fields in eastern
North America, have not. Although individuals of this parasitoid differ
genetically in their ability to parasitize pea aphids, no consistent difference
in virulence is evident in different crop habitats (Henter 1995; Hufbauer
2001).
As we noted in chapter 3, populations of the Argentine ant (
Linep-
ithema humile
) in North America form supercolonies in which individu-
als show little or no aggression toward members of different colony units.
This appears to be the result of a combination of loss of genetic variabil-
ity at the time of the colonization event and selection against aggression
following establishment in North America (Tsutsui et al. 2003).
Insect vectors of animal disease have invaded many new world regions,
and some have shown rapid evolutionary adjustment.The mosquito
Aedes
aegypti
, for example, is a vector for the disease agents of both yellow fever
and dengue, both viral diseases affecting humans. The mosquito exists as
two subspecies,
formosus
, native to tropical forests of Africa, and
aegypti
,
now worldwide in tropical environments close to human habitation (Fail-
