Ecology. 2014 Apr;95(4):910-9. doi: 10.1890/13-0447.1.
Reproductive success in flowering plants is influenced by the morphology and timing of reproductive structures as well as the density of surrounding conspecifics. In species with separate male and female flower phases, successful pollen transfer is also expected to vary with the density and ratio of surrounding male and female flowers. Increased density of surrounding flowers may increase pollinator visitation rates, but the densities of male and female flowers will determine the availability of pollen and the strength of competition for pollen receipt. Here we (1) quantify the influence of surrounding plant density on total seasonal fruit and seed production, (2) quantify the influence of sexual neighborhood (surrounding sex ratio and densities of male- and female-phase flowers) on fruit and seed production for individual flowers presented within the season, and (3) compare the influence of plant density on fitness to that of focal plant phenotype, specifically stigma-nectary distance and plant height, in a natural population of the pollen-limited, hummingbird-pollinated hermaphrodite Lobelia cardinalis. These relationships were examined at four spatial scales (10, 20, 50, and 100 cm). By examining temporal and spatial scales we found that (1) total seed production per plant decreased with increasing plant density at the smallest scale but increased with increasing density at all larger scales; (2) at any given time, a female-phase flower benefited from a higher density of surrounding male-phase flowers and a lower density of surrounding female-phase flowers; (3) when sex ratio was explicitly analyzed, a female-phase flower benefited from a lower proportion of surrounding female flowers as well as a lower total flower density; and (4) at the whole-plant level, taller plants were more likely to produce fruit (even when accounting for total number of flowers produced), consistent with pollinator preference for taller floral displays. Our results suggest that the local density of male and female flowers (and surrounding sex ratio) influences successful pollen transfer, implying that the local floral environment may shape how attraction traits like plant height are related to fitness.
开花植物的生殖成功受生殖结构的形态和时间以及周围同种植物密度的影响。在具有雌雄异熟花阶段的物种中，成功的花粉传递也有望随周围雄性和雌性花的密度和比例而变化。周围花的密度增加可能会增加传粉者的访问率，但雄性和雌性花的密度将决定花粉的可获得性以及对花粉接收的竞争强度。在这里，我们（1）量化了周围植物密度对整个季节果实和种子产量的影响，（2）量化了性邻居（周围的性别比例和雌雄异熟花阶段的花的密度）对季节内呈现的单个花的果实和种子产量的影响，（3）在具有花粉限制的、蜂鸟传粉的雌雄同体山梗菜的自然种群中，将植物密度对适合度的影响与焦点植物表型（具体为柱头蜜腺距离和植物高度）进行了比较。这些关系在四个空间尺度（10、20、50 和 100 cm）上进行了检验。通过检查时间和空间尺度，我们发现（1）在最小尺度上，每株植物的总种子产量随植物密度的增加而减少，但在所有较大尺度上随密度的增加而增加；（2）在任何给定时间，雌花花期受益于周围雄花花期的高密度和周围雌花花期的低密度；（3）当明确分析性别比例时，雌花花期也受益于周围雌花比例较低和总花密度较低；（4）在整个植株水平上，较高的植物更有可能产生果实（即使考虑到产生的总花数），这与传粉者对较高的花展示的偏好一致。我们的研究结果表明，雌雄花（和周围的性别比例）的局部密度影响成功的花粉传递，这意味着局部的花环境可能会影响像植物高度这样的吸引力特征与适合度的关系。
