The earlier the better? Nesting timing and reproductive success in subalpine cavity-nesting bees

1. Reproductive timing can affect an organism’s production of offspring and its offspring’s success, both of which contribute to its overall fitness. In seasonal environments, the timing of reproductive activity may be restricted to short periods of the year owing to numerous potential selective pressures such as variation in daylength, weather, food availability, predation, or competition. 2. We documented the relationships between reproductive timing and individual reproductive success (total reproductive output and offspring success) in subalpine populations of five cavity-nesting solitary bee species. We also examined the relationships between bee reproductive success and environmental variables that are likely ultimate drivers of bee phenology in subalpine environments (i.e., seasonality of floral resource abundance and temperature). 3. Over six years, we recorded solitary bee nesting timing, egg production, and offspring success using artificial nesting structures (“trap-nes...1. 繁殖时间可影响生物体的子代产生量与子代存活成功率，二者共同决定生物体的整体适合度（fitness）。在季节性环境中，受日照时长变化、天气状况、食物可获得性、捕食压力或种间竞争等多种潜在选择压力的影响，繁殖活动的时间窗口往往被限制在一年中的较短时段内。 2. 本研究针对5种筑巢于洞穴的独居蜂的亚高山种群，记录了繁殖时间与个体繁殖成功率（总繁殖产出及子代成功率）之间的关联。同时，我们还探究了蜂类繁殖成功率与环境变量之间的关系——这些环境变量极有可能是亚高山环境中蜂类物候（phenology）的核心驱动因子，即花资源丰度的季节动态与温度变化。 3. 本研究历时6年，通过人工筑巢结构（"诱巢（trap-nest）"）记录了独居蜂的筑巢时间、产卵量及子代成功率。