Biology Reference
In-Depth Information
Evolutionary adaptability is favored by other genetic features (Lee
2002). In particular, the fraction of additive genetic variance within the
genome strongly influences adaptive capability. Additive genetic variance
represents allelic variability through which selection can progressively
modify a quantitative characteristic by increasing the frequency of partic-
ular alleles. Genetic loci that show additive genetic variation are termed
quantitative trait loci. Epistasis, an interaction in which one gene influ-
ences the expression of another, can also facilitate rapid evolutionary
change. The potential for chromosomal restructuring by inversions,
translocations, duplications, or other changes that can influence gene
action is another influential factor. The extent to which selection results
in trade-offs of adaptive gain in one feature and loss of adaptation in
another can also influence the capacity for evolutionary change.
For those aliens with favorable genetic variability, the particular habi-
tat conditions and biotic pressures of the new environment often result in
rapid evolutionary adjustments (Thompson 1998). Physical and chemical
conditions differing from those of the native region select for adaptation
to the new habitat. Biotic pressures due to predators, parasites, disease
agents, and competitors are also altered. In some cases, these conditions
are relaxed, favoring rapid population growth and high reproductive suc-
cess by aliens. In these cases, selection may favor reallocation of resources
from defense to growth and reproduction. In other cases, new biotic asso-
ciates may be exploited for food or for pollination and seed dispersal. In
time, many of the new associates may begin to act as predators, parasites,
diseases, or competitors.
In general, the population growth that often follows colonization of a
new geographical area is highly favorable for rapid evolution (Reznik and
Ghalambor 2001).The success of an invader in spreading through a new
region is often the product of its ability to adapt to the new conditions it
encounters (García-Ramos and Rodríguez 2002). High dispersal ability
may introduce populations to new areas to which they are poorly adapted
and in which they fail to become established. In time, however, evolution-
ary adaptation by more slowly spreading populations may result in suc-
cessful establishment in the same new areas.
Alien Species and Evolutionary Change by Natives
Evolutionary change flows outward from established alien populations,
affecting the entire biotic community to some degree. Alien plants can
alter conditions of the physical environment, changing physical condi-
tions such as light intensity, chemical conditions such as soil salinity, and
