Data from: Frequency dependence and ecological drift shape coexistence of species with similar niches

The coexistence of ecologically similar species might be counteracted by ecological drift and demographic stochasticity, both of which erode local diversity. With niche differentiation, species can be maintained through performance trade-offs between environments, but trade-offs are difficult to invoke for species with similar ecological niches. Such similar species might then go locally extinct due to stochastic ecological drift but there is little empirical evidence for such processes. Previous studies have relied on biogeographical surveys and inferred process from pattern, while experimental field investigation of ecological drift are rare. Mechanisms preserving local species diversity, such as frequency-dependence (e. g. rare-species advantages), can oppose local ecological drift, but the combined effects of ecological drift and such counteracting forces have seldom been investigated. Here, we investigate mechanisms between coexistence of ecologically similar but strongly sexually differentiated damselfly species (Calopteryx virgo and C. splendens). Combining field surveys, behavioral observations, experimental manipulations of species frequencies and densities, and simulation modelling, we demonstrate that species coexistence is shaped by the opposing forces of ecological drift and negative frequency-dependence (rare species advantage), generated by interference competition. Stochastic and deterministic processes therefore jointly shape coexistence. The role of negative frequency-dependence in delaying the loss of ecologically similar species, such as those formed by sexual selection, should therefore be considered in community assembly, macroecology, macroevolution and biogeography.

生态相似物种的共存可能会被生态漂变（ecological drift）与种群统计随机性（demographic stochasticity）所抵消，二者均会削弱局域物种多样性。借助生态位分化（niche differentiation），物种可通过不同环境间的性能权衡（performance trade-offs）得以维持，但对于生态位相似的物种而言，这类权衡难以适用。此类生态位相似的物种或许会因随机生态漂变而在局域灭绝，但目前针对此类过程的实证证据极度匮乏。既往研究多依赖生物地理学调查，通过格局推断背后的过程，而针对生态漂变的野外实验研究则十分罕见。维持局域物种多样性的机制，例如频率依赖（frequency-dependence，如稀有种优势），可对抗局域生态漂变，但生态漂变与这类拮抗力量的联合效应却鲜有被探究。本研究针对生态位相似但具有显著性别分化的豆娘物种（阔翅豆娘Calopteryx virgo与C. splendens）的共存机制展开探究。结合野外调查、行为观察、物种频率与密度的实验操控，以及模拟建模，我们证实物种共存由生态漂变与干扰竞争（interference competition）所引发的负频率依赖（稀有种优势）这两种拮抗力量共同塑造。因此，随机性与确定性过程共同调控物种共存。负频率依赖在延缓生态位相似物种（如由性选择所形成的物种）的丧失过程中所发挥的作用，应当被纳入群落组装、宏生态学、宏进化以及生物地理学的研究框架之中。