The genus Nicotiana contains over 60 species. Interestingly, the nicotine content of leaves varies widely among species. For instance, a study reported nicotine contents ranging from 0 to >9000 ug/g of leaf tissue in 36 species. If nicotine is necessary to deter herbivores, why don’t all species produce high levels? Briefly provide two evolutionary reasons explaining i why this variation in nicotine concentration may occur.