Compensatory responses of vital rates attenuate impacts of competition on population growth and promote coexistence

Competition is among the most important factors regulating plant population and community dynamics, but we know little about how different vital rates respond to competition and jointly determine population growth and species coexistence. We conducted a field experiment and parameterized integral projection models to model the population growth of 14 herbaceous plant species in the absence and presence of neighbours across an elevation gradient (284 interspecific pairs). We found that suppressed individual growth and seedling establishment contributed the most to competition-induced declines in population growth, though vital rate contributions varied greatly between species and with elevation. In contrast, size-specific survival and flowering probability and seed production were frequently enhanced under competition (in 92% of species pairs). These compensatory responses of vital rates significantly reduced niche overlap and stabilized coexistence. Our study highlights the importance of demographic processes for regulating community dynamics, which has often been neglected by classic coexistence theories.