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their parental plants. Moon et al. (2007) showed that there was no e ffect of Bt-transgene in
field trials with low ambient herbivory levels. Taken together, these studies suggest that Bt-
transgene produces an increased plant fitness consequence under moderate to high herbivore
damage, but not for low or no herbivory pressure.
As the fitness advantage of insect–resistant (Bt-transgene) is detected, especially under
high herbivory, the resistant plants are expected to suppress the growth of susceptible ones in
mixed populations. Accordingly, the competition interaction between resistant and susceptible
plants will determine in part the population dynamics. Ramachandran et al. (2000) found the
insect-resistant transgenic plants were superior competitors in mixed stands with susceptible
individuals. However, the dynamic of mixed populations including resistant and susceptible
plants might be a complex process, because it depends on certain factors, such as intensity of
herbivory, r esource l evel a nd r elative a bundance of r esistant pl ants ( Verkaar 1987 ). A s t he
invasion a nd colonization of r esistant pl ants (transgenic h ybrids o r crops), t he competition
between t he t wo classes ( resistant vs . s usceptible) de creased, but t he competition a mong
resistant p lants ( intraclass c ompetition) in creased. T herefore, t he fate o f w ild relatives
depends at least in part on the competition interaction between resistant and susceptible plants.
The population will be either in equilibrium where resistant and susceptible plants coexist in a
stable pr oportion or s usceptible p lants b eing r eplaced b y resistant p lants th at b oost th e
population de mography. T hese d ata gaps f ace us, a lthough i t i s crucial t o unde rstand t he
ecological and evolutionary consequences in the process of introgression from crops to wild
relative populations.
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