PREMISE Variation in local density and sex ratio in dioecious plants can affect mating success through the actions of pollen vectors, principally generalist insects or wind. Increased density and male-biased sex ratios should promote pollen transfer and seed production, but their combined effects have not been investigated for ambophilous species, which exhibit both insect and wind pollination. METHODS We manipulated density (low vs. high) and sex ratio (1:1 vs. 3:1 male-biased) in arrays of dioecious ambophilous Thalictrum pubescens. We quantified visitation rates and foraging times to examine whether pollinators exhibited sex-specific preferences and determined the seed set of arrays. RESULTS Pollinators visited more plants per foraging bout at high than low density. Visitation rates and foraging times of visitors were greater for male than for female plants but did not depend on the density or sex ratio of arrays. However, whereas solitary bees displayed a strong preference for males, hover flies were indifferent to plant sex phenotype. Solitary bees also visited significantly more plants per foraging bout than hover flies. There was a significant interaction between density and sex ratio on seed set. At low density, seed set was greater for 3:1 than for 1:1 arrays, but at high density the opposite pattern occurred. CONCLUSIONS The demographic factors we investigated had complex influences on pollinator foraging behavior and patterns of seed set. Several factors may explain our results, including the influence of density and sex ratio on pollen export from arrays, grooming by pollinators, and the contribution of wind pollination.

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局部密度和性别比对两栖开花植物授粉的影响

前提 雌雄异株植物的局部密度和性别比例的变化会通过花粉载体（主要是通才昆虫或风）的作用影响交配成功。增加的密度和男性偏向的性别比例应该会促进花粉转移和种子生产，但尚未对兼具昆虫和风授粉的两栖物种研究它们的综合影响。方法我们在雌雄异株的两栖梭鱼阵列中操纵密度（低与高）和性别比（1:1 与 3:1 男性偏向）。我们量化了访问率和觅食时间，以检查传粉媒介是否表现出性别特异性偏好并确定阵列的种子集。结果 传粉者在高密度下比低密度每轮觅食时访问的植物更多。雄性植物的访客访问率和觅食时间大于雌性植物，但不依赖于阵列的密度或性别比。然而，尽管孤独的蜜蜂表现出对雄性的强烈偏好，但悬停蝇对植物的性别表型无动于衷。与悬停蝇相比，孤独的蜜蜂每次觅食时访问的植物也多得多。种子集密度和性别比之间存在显着的相互作用。在低密度下，3:1 阵列的种子集大于 1:1 阵列，但在高密度下出现相反的模式。结论 我们调查的人口统计因素对传粉媒介的觅食行为和结实模式有着复杂的影响。有几个因素可以解释我们的结果，包括密度和性别比对阵列花粉输出的影响，传粉者的梳理，