Evolution of Increased Competitive Ability in Invasive Nonindigenous Plants: A Hypothesis

There are very few valid generalizations about invasive species, so that it is only possible to make weak, probabilistic predictions about which species will invade (Gilpin 1990; Daehler Bazzaz et al. 1987; Fagerstrom 1989; Herms Lerdau et al. 1995). The environmental constraint hypothesis (Bryant et al. 1988), however, predicts that the evolution of defence mechanisms against herbivory will result in only minor reductions in growth. Resource availability is then the primary force determining whether there is surplus photosynthate available for allocation to secondary metabolism.