Some evolutionary radiations produce a number of closely-related species that continue to coexist. In such plant systems, when pre-pollination barriers are weak, relatively strong post-pollination reproductive barriers are required to maintain species boundaries. Even when post-pollination barriers are in place, however, reproductive interference and pollinator dependence may strengthen selection for pre-pollination barriers. We assessed whether coexistence of species from the unusually speciose Erica genus in the fynbos biome, South Africa, is enabled through pre-pollination or post-pollination barriers. We also tested for reproductive interference and pollinator dependence. We investigated this in natural populations of three bird-pollinated Erica species (Erica plukenetii, E. curviflora and E. coccinea), which form part of a large guild of congeneric species that co-flower and share a single pollinator species (Orange-breasted Sunbird Anthobaphes violacea). At least two of the three pre-pollination barriers assessed (distribution ranges, flowering phenology and flower morphology) were weak in each species pair. Hand-pollination experiments revealed that seed set from heterospecific pollination (average 8%) was significantly lower than seed set from outcross pollination (average 50%), supporting the hypothesis that species boundaries are maintained through post-pollination barriers. Reproductive interference, assessed in one population by applying outcross pollen three hours after applying heterospecific pollen, significantly reduced seed set compared to outcross pollen alone. This may drive selection for traits that enhance pre-pollination barriers, particularly given that two of the three species were self-sterile, and therefore pollinator dependent. This study suggests that post-pollination reproductive barriers could facilitate the coexistence of congeneric species, in a recent radiation with weak pre-pollination reproductive barriers.

一些进化辐射会产生许多紧密共存的物种，并继续共存。在这样的植物系统中，当授粉前的屏障较弱时，需要相对较强的授粉后的生殖屏障来维持物种边界。但是，即使存在授粉后的障碍，生殖干扰和授粉媒介的依赖性也可能会增强对授粉前障碍的选择。我们评估了通过授粉前或授粉后的壁垒是否能够使南非fynbos生物群落中异常特殊的埃里卡属的物种共存。我们还测试了生殖干扰和授粉媒介的依赖性。我们在三种鸟类授粉的Erica物种的自然种群中进行了调查（埃里卡plukenetii，E. curviflora和E.红花），大公会同类物种的共花和共享一个传粉物种（橙胸太阳鸟的哪个组成部分Anthobaphes violacea）。在每个物种对中，评估的三个授粉前障碍中的至少两个（分布范围，开花物候和花朵形态）较弱。人工授粉实验表明，异种授粉的种子集（平均8％）明显低于异花授粉的种子集（平均50％），支持了通过传粉后屏障维持物种边界的假设。与异源花粉相比，异源花粉施用三小时后异源花粉在一个种群中进行的生殖干扰评估显着降低了结实率。这可能会促使选择增强传粉前障碍的性状，特别是考虑到三个物种中的两个是自育的，因此依赖传粉媒介。