Data_Sheet_1_Emergence phenology of the giant salmonfly and responses by birds in Idaho river networks.pdf

Emergence of adult aquatic insects from rivers is strongly influenced by water temperature, and emergence timing helps to determine the availability of this ephemeral food resource for birds and other terrestrial insectivores. It is poorly understood how spatial heterogeneity in riverine habitat mediates the timing of emergence. Such spatiotemporal variation may have consequences for terrestrial insectivores that rely on aquatic-derived prey resources. We investigated emergence phenology of the giant salmonfly, Pteronarcys californica, at three spatial scales in two Idaho river networks. We examined the influence of tributary confluences on salmonfly emergence timing and associated insectivorous bird responses. Salmonfly emergence timing was highly variable at the basin-scale during the period we sampled (May–June). Within sub-drainage pathways not punctuated by major tributaries, emergence followed a downstream-to-upstream pattern. At the scale of reaches, abrupt changes in thermal regimes created by 10 major tributary confluences created asynchrony in emergence of 1–6  days among the 20 reaches bracketing the confluences. We observed 10 bird species capturing emerged salmonflies, including 5 species typically associated with upland habitats (e.g., American robin, red-tailed hawk, American kestrel) but that likely aggregated along rivers to take advantage of emerging salmonflies. Some birds (e.g., Lewis’s woodpecker, western tanager, American dipper) captured large numbers of salmonflies, and some of these fed salmonflies to nestlings. Emergence asynchrony created by tributaries was associated with shifts in bird abundance and richness which both nearly doubled, on average, during salmonfly emergence. Thermal heterogeneity in river networks created asynchrony in aquatic insect phenology which prolonged the availability of this pulsed prey resource for insectivorous birds during key breeding times. Such interactions between spatial and temporal heterogeneity and organism phenology may be critical to understanding the consequences of fluxes of resources that link water and land. Shifts in phenology or curtailment of life history diversity in organisms like salmonflies may have implications for these organisms, but could also contribute to mismatches or constrain availability of pulsed resources to dependent consumers. These could be unforeseen consequences, for both aquatic and terrestrial organisms, of human-driven alteration and homogenization of riverscapes.

河流中水生成虫的羽化过程受水温影响显著，而羽化时间是决定鸟类及其他陆生食虫动物可获取该短期食物资源的关键因素。目前学界对河流生境的空间异质性如何调控昆虫羽化时间的机制仍知之甚少。这类时空变异可能对依赖水生来源猎物的陆生食虫动物产生连锁影响。
本研究在爱达荷州的两个河网中，于三个空间尺度上开展了巨型鲑蝇（Pteronarcys californica）的羽化物候学研究，探讨了支流汇口对鲑蝇羽化时间及相关食虫鸟类响应的影响。
本次采样时段为5至6月，流域尺度下鲑蝇的羽化时间存在高度变异。在未被主要支流截断的次级水道中，羽化呈现从下游到上游的顺向模式。在河段尺度上，10处主要支流汇口造成的水热状况突变，使得汇口周边20个河段的羽化时间出现1至6天的异步性。
我们观测到10种鸟类取食羽化后的鲑蝇，其中5种通常栖息于高地生境（如美洲知更鸟、红尾鵟、美洲红隼），但它们会沿河流聚集以利用鲑蝇羽化的食物资源。部分鸟类（如刘易斯啄木鸟、西唐纳雀、美洲河乌）会大量取食鲑蝇，其中部分个体还会将鲑蝇喂食雏鸟。
支流引发的羽化异步性与鸟类种群丰度和物种丰富度的变化显著相关：在鲑蝇羽化期，这两项指标平均近乎翻倍。河网的热异质性使得水生昆虫物候出现异步性，从而在食虫鸟类的关键繁殖期内，延长了这类脉冲式猎物资源的可利用时长。
空间与时间异质性以及生物物候之间的这类相互作用，对于理解连接水陆生态系统的资源通量效应至关重要。类似鲑蝇这类生物的物候偏移或生活史多样性缩减，不仅会对其自身产生影响，还可能引发生态错配，或是限制依赖这类脉冲式资源的消费者的可获取量。人类活动驱动的河流景观改造与同质化，可能会对水生与陆生生物带来上述未被预见的负面影响。