They included a separate box explaining pitfalls in calculating the basic reproductive ratio from nonlinear models and noted its nonuniqueness, calculating two distinct values for R 0 . However, they were unable to decide which value was correct. The authors conclude by stating that "Although nonlinear differential equations are invaluable tools for studying epidemics, they should not serve as the primary basis for the determination of R 0 ." Cunniffe and Gilligan [62] considered the effects of host demography upon the outcomes for invasion, persistence and control of pathogens in a model for botanical epidemics. They used the next-generation method to calculate