Temporal partitioning of diurnal bird and nocturnal small mammal visitors to a winter flowering endemic succulent

Floral nectar is an important attractant and reward for visitors, and is often produced in synchrony with peak activity of pollinators. <i>Aloe peglerae</i> flowers in winter, and previous studies have shown that it is pollinated primarily by diurnal generalist birds, with small mammals making additional contributions to pollination at night. Nectar produced during the day is the main attractant and reward for birds, but the nectar rewards available to small mammals are unknown. This paper investigates nectar availability in <i>Aloe peglerae</i>, because small mammals may be feeding on remaining, or freshly produced, nectar at night. Nectar availability over a 24-hour period was measured in screened and unscreened plants (<i>n</i> = ten plants per treatment), and the associated partitioning of visits by diurnal birds and nocturnal small mammals assessed. Nectar is constantly available over 24-hours, but in different quantities. Nectar volume of screened (nectar availability) and unscreened (standing crop) plants, is significantly higher early in the morning after sunrise, compared with all other sampling periods during the 24-hour period. Nectar concentration did not vary over 24-hours, averaging 11.5 ± 0.4% w/w (unscreened) across the entire 24-hour period. Peaks in visits by different guilds occurred at periods (i.e. diurnal birds and nocturnal small mammals) when nectar availability was high. <i>Aloe peglerae</i> has higher daytime nectar production, when its primary pollinators are most active, but the continual, albeit reduced, nectar availability at night attracts small mammals. Mobile diurnal birds, and less-mobile nocturnal small mammals, both rely on this nectar resource during dry and cold South African winters and, in turn, are important pollinators for this Critically Endangered <i>Aloe</i> species.

花部花蜜（floral nectar）是吸引访花者并为其提供报酬的重要物质，其分泌通常与传粉者（pollinators）的活动高峰期同步。皮尔芦荟（*Aloe peglerae*）于冬季开花，此前研究表明，其主要传粉者为日间活动的广食性鸟类（generalist birds），小型哺乳动物（small mammals）则在夜间为其补充传粉服务。日间分泌的花蜜是鸟类主要的吸引信号与报酬来源，但小型哺乳动物可获取的花蜜报酬仍不明晰。本研究针对皮尔芦荟的花蜜可获得性（nectar availability）展开调查，因小型哺乳动物可能会取食夜间残留或新分泌的花蜜。研究在套袋处理组与未套袋处理组植株（每组各10株，*n*=10）中监测了24小时内的花蜜动态：其中套袋组用以测定花蜜可获得性，未套袋组则用以测定自然状态下的花蜜贮量（standing crop），并评估了日间鸟类与夜行性小型哺乳动物的访花类群分配特征。花蜜在24小时内始终存在，但分泌量存在波动。日出后的清晨时段，套袋植株与未套袋植株的花蜜体积，均显著高于24小时内其余所有采样时段。花蜜浓度在24小时内无显著变化，整个监测周期内未套袋植株的花蜜浓度平均值为11.5 ± 0.4% 重量/重量（w/w）。不同取食类群（guilds）的访花高峰均出现在花蜜可获得性较高的时段，即日间鸟类活动的日间与夜行性小型哺乳动物活动的夜间。皮尔芦荟在其主要传粉者最为活跃的日间分泌更多花蜜，但尽管夜间花蜜分泌量有所降低，持续存在的花蜜仍能吸引小型哺乳动物。活动能力较强的日间鸟类与活动能力较弱的夜行性小型哺乳动物，在南非干燥寒冷的冬季均依赖该花蜜资源，而它们也正是这一极危（Critically Endangered）芦荟属物种的重要传粉者。