Coexistence of annual plants under competition and reproductive interference

Abstract

In natural ecosystems, community dynamics are driven by diverse interactions operating through both ecological and reproductive processes. Although theory predicts that these processes jointly generate complex and contingent dynamics through the interplay of stabilizing (negative frequency dependence arising from niche differences) and destabilizing effects (positive frequency dependence caused by reproductive interference), empirical tests of this prediction remain scarce. Here, we combined experimental and theoretical approaches to investigate the dynamics of two congeneric annual plant species (Commelina) experiencing both ecological competition and reproductive interference. Our empirically parameterized model revealed a large niche difference and mutual reproductive interference. However, the reproductive interference was not strong enough to generate pronounced contingency of community dynamics on initial conditions. Instead, coexistence was the most likely outcome regardless of initial species composition. Parameter exploration indicated that the weak contingency arose because reproductive assurance strategies of Commelina species buffered the minority disadvantage caused by reproductive interference. These findings provide empirical evidence that reproductive interference does not necessarily destabilize coexistence and that it may be outweighed by ecological niche and fitness differences. Our study highlights the importance of integrating ecological and reproductive processes towards better prediction of community dynamics. Significant statement Species interactions can both promote and undermine coexistence. Ecological niche differences can promote coexistence by favoring rare species, whereas reproductive interference can favor more abundant species and destabilize coexistence. How these opposing forces jointly shape community dynamics remains poorly understood. We combined experiments and mathematical approaches to examine their simultaneous effects on the coexistence of two closely related annual plants. Despite mutual reproductive interference, our empirically calibrated model showed that coexistence was the most likely outcome irrespective of initial species abundance. Reproductive interference had limited effects, likely because selfing before interspecific pollination provided reproductive assurance. Our findings demonstrate that reproductive interference does not necessarily destabilize coexistence and highlight the importance of integrating ecological and reproductive processes to predict community dynamics.