in Nicotiana attenuata, the induced production of nicotine as a chemical resistance factor
was associated with metabolic costs, but provided a fitness benefit when plants were
under attack by herbivores (Baldwin 1998; see also Steppuhn and Baldwin this volume).
Although these findings should not be generalized and a defensive role should
not be assumed for all plant responses to wounding and herbivory, the prevalence
of inducible resistance traits in present day plant-herbivore systems implies that
such responses are likely the result of natural selection imposed by insect herbivores
during evolution.