PS 43-178 - Germination phenology alters species coexistence outcomes

Abstract: Species-specific phenological responses to changing climate are reshuffling the timing of species interactions, however we don’t understand of the consequences of this phenological change for species’ population dynamics and community composition. Coexistence theory provides a useful conceptual and mathematical framework for examining how species’ differences, including phenology, can shape community composition, but experimental studies of how phenological differences affect species interactions and coexistence are lacking. In this study, we experimentally manipulated the timing of germination for five annual plant species from southern California and conducted pairwise competition experiments to quantify how phenological shifts may impact coexistence. We found that in some cases phenological shifts may help stabilize coexistence when they confer an advantage for competitively dominant species, but in other cases may promote dominance by competitively superior species. While phenological differences among species have typically been considered a form of niche partitioning, growing evidence suggests that stronger effects on fitness inequalities may lead to competitive exclusion.