The Grey-backed Shrike parents adopt brood survival strategy in both the egg and nestling phases

Background:Great diversity exists in the parenting pattern of altricial birds,which has long been considered as an adaptive response to specific environmental conditions but not to their life-history style.Methods:We examined the egg-laying and nestling-raising pattern of the Grey-backed Shrike(Lanius tephronotus)that breeds only once a year on the Tibetan Plateau.We compared the dietary composition to that of its sympatric competitor,the Brown-cheeked Laughing Thrush(Trochalopteron henrici)that breeds twice a year.Results:Female Grey-backed Shrikes produced a fixed clutch size of five,with increasing egg size by their laying sequence.The last offspring in the brood is disadvantageous in the size hierarchy because it hatches later.However,they had the largest fledgling body mass.These findings indicate that Grey-backed Shrikes adopt the brood survival strategy in both the egg and nestling phases.Moreover,males and females exhibit no sexual division in providing parental care as they made an equal contribution to the total amount of food delivered to their brood.This parenting pattern of Grey-backed Shrikes,as well as their dietary items,differ significantly from those of the Brown-cheeked Laughing Thrush.Conclusions:We suggest that the differentiation in life-history style between sympatric competitors,rather than a behavioral response to specific environmental conditions,plays a decisive role in driving avian parenting strategy diversification.

互利作用促进了高山树线幼苗的存活

高山树线被视为记录气候变化对树木和森林影响的生态监测器。迄今为止,大多数树线研究都集中在气候变化如何驱动树线动态的变化。然而,关于生物相互作用如何调节树线变化,特别是在树木更新这一树线动态的瓶颈方面,人们知之甚少。本研究假设种间和种内促进作用决定了高山树线树苗的定居和存活。为了验证这一假设,我们在青藏高原东南部的色季拉山高山树线交错区(海拔4300–4500 m)的3个生长生境(林冠内、林冠外和草地)中共计移植了630株不同年龄(4–6年、7–9年和10–15年)的急尖长苞冷杉(Abies georgei var.smithii)幼苗,连续3年监测了移植后幼苗的微气候、高度生长、死亡率和叶片功能性状。结果发现,叶片功能性状的变化是由微气候驱动的。移植后,叶片可溶性糖和淀粉浓度以及C:P比增加,而叶面积减小。幼苗的资源利用逐渐转向更保守的策略,其背后机制主要受到了生理性状(非结构性碳水化合物和植物养分)的介导。同时,由结构方程模型发现太阳辐射、温度和水分条件在植物相互作用下,通过介导叶片形态性状的变化最终影响了幼苗的死亡率和年生长。上述研究结果表明,植物间的互利作用通过改变太阳辐射和叶片功能性状,最终在决定幼苗生长和存活上起到至关重要的作用,同时也为理解全球气候变化背景下高山树线动态变化的驱动机制提供了新的见解。