Fenner School of Environment and Society, Australian National University, Linnaeus Way, Acton, Canberra 2601, Australia.
School of Agricultural, Environmental and Veterinary Sciences, Charles Sturt University, Albury, New South Wales, Australia.
Proc Biol Sci. 2022 Jul 13;289(1978):20220358. doi: 10.1098/rspb.2022.0358.
Mistletoes are hemiparasitic plants and keystone species in many ecosystems globally. Given predicted increases in drought frequency and intensity, mistletoes may be crucial for moderating drought impacts on community structure. Dependent on host vascular flows, mistletoes can succumb to stress when water availability falls, making them susceptible to mortality during drought. We counted mistletoe across greater than 350 000 km of southeastern Australia and conducted standardized bird surveys between 2016 and 2021, spanning a major drought event in 2018-2019. We aimed to identify predictors of mistletoe abundance and mortality and determine whether mistletoes might moderate drought impacts on woodland birds. Live mistletoe abundance varied with tree species composition, land use and presence of mistletoebirds. Mistletoe mortality was widespread, consistent with high 2018/2019 summer temperatures, low 2019/2020 summer rainfall and the interaction between summer temperatures and rainfall in 2019/2020. The positive association between surviving mistletoes and woodland birds was greatest in the peak drought breeding seasons of 2018/2019 and 2019/2020, particularly for small residents and insectivores. Paradoxically, mistletoes could moderate drought impacts on birds, but are themselves vulnerable to drought-induced mortality. An improved understanding of the drivers and dynamics of mistletoe mortality is needed to address potential cascading trophic impacts associated with mistletoe die-off.
槲寄生是半寄生植物，也是全球许多生态系统中的关键物种。鉴于干旱频率和强度的预测增加，槲寄生可能对缓解干旱对群落结构的影响至关重要。槲寄生依赖于宿主的血管流动，如果水分供应减少，它们可能会因压力而死亡，因此在干旱期间容易死亡。我们在澳大利亚东南部超过 35 万公里的范围内对槲寄生进行了计数，并在 2016 年至 2021 年期间进行了标准化鸟类调查，涵盖了 2018-2019 年的一次主要干旱事件。我们旨在确定槲寄生丰度和死亡率的预测因子，并确定槲寄生是否可能缓解干旱对林地鸟类的影响。活槲寄生的丰度随树种组成、土地利用和槲寄生鸟的存在而变化。槲寄生的死亡率很普遍，这与 2018/2019 年夏季的高温、2019/2020 年夏季的低降雨量以及 2019/2020 年夏季温度和降雨量之间的相互作用一致。在 2018/2019 年和 2019/2020 年的干旱高峰期繁殖季节，存活的槲寄生与林地鸟类之间的正相关关系最大，尤其是对小型居民和食虫动物而言。矛盾的是，槲寄生可以缓解干旱对鸟类的影响，但它们本身也容易受到干旱引起的死亡率的影响。需要更好地了解槲寄生死亡率的驱动因素和动态，以解决与槲寄生死亡相关的潜在级联营养影响。
