Data from: A test of the effects of timing of a pulsed resource subsidy on stream ecosystems

AbstractSpatial resource subsidies can alter bottom-up and top-down forces of community regulation across ecosystem boundaries. Most subsidies are temporally variable, and recent theory has suggested that consumer-resource dynamics can be stabilized if the peak timing of a subsidy is desynchronized with that of prey productivity in the recipient ecosystem. However, magnitude of consumer responses per se could depend on the subsidy timing, which may be a critical component for community dynamics and ecosystem processes. The aim of this study was to test (1) whether a recipient consumer (cutthroat trout) responds differently to a resource subsidy occurring early in its growing season than to a subsidy occurring late in the season, and, if this is the case, (2) whether the timing-dependent consumer response has cascading effects on communities and ecosystem functions in streams. To test those hypotheses, we conducted a large-scale field experiment, in which we directly manipulated the timing of augmentation of the terrestrial invertebrates that enter stream (i.e., peak timing of June-August vs. August-October), keeping constant the total amounts of the invertebrates entered. We found large increases in the individual growth rate and population biomass of the cutthroat trout, in response to the early resource pulse, but not to the late pulse. This timing-dependent consumer response cascaded down to reduce benthic invertebrates and leaf break-down rate, and increased water nutrient concentrations. Furthermore, the early resource pulse resulted in higher maturity rate of the cutthroat trout in the following spring, demonstrating the importance of the subsidy timing on long-term community dynamics via the consumer's numerical response. Our results emphasize the need to acknowledge timing-dependent consumer responses in understanding the effects of subsidies on communities and ecosystem processes. Elucidating the mechanisms by which consumers effectively exploit pulsed subsidies is an important avenue to better understand community dynamics in spatially coupled ecosystems., Usage notestrout_stomachStomach contents of trout in each season in each treatment reachtrout_growthSpecific growth rate of individual trout in each season in each treatment reachestrout_nexcretionN excretion by individual trout in each season in each treatmenttrout_pexcretionP excretion by individual trout in each season in each treatmenttrout_maturityMaturation of trout in the spawning seasonbenthicsBiomasses of benthic invertebrates in each season in each treatmentbenthic algaeBiomass of benthic algae in each season in each treatment reachesleaf_breakdownLeaf break-down rate in each season in each treatmentstreamwater_nutrientsNH3-N and SRP concentrations in stream water in each season in each treatment reaches摘要 空间资源补给（resource subsidy）可改变跨生态系统边界的群落调控上行效应（bottom-up）与下行效应（top-down）。多数资源补给具有时间变异性，近期理论研究表明，若补给峰值时间与接收生态系统中猎物生产力的峰值时间不同步，则可稳定消费者-资源动态。然而，消费者响应的强度本身可能依赖于补给时间，这或许是调控群落动态与生态系统过程的关键要素。本研究旨在验证两项假设：其一，接收生态系统中的消费者（斑尾红点鲑，cutthroat trout）对生长季早期出现的资源补给与生长季晚期出现的补给是否会产生差异化响应；其二，若存在此类差异，那么依赖于时间的消费者响应是否会对溪流群落及生态系统功能产生级联效应。为验证上述假设，本研究开展了大规模野外操控实验：直接调控向溪流输入的陆生无脊椎动物补给的峰值时间（即6-8月峰值与8-10月峰值），并保持输入的无脊椎动物总数量不变。研究结果显示，相较于晚期补给，早期的资源脉冲（resource pulse）可显著提升斑尾红点鲑的个体生长速率与种群生物量。这种依赖于时间的消费者响应进一步产生级联效应：降低了底栖无脊椎动物（benthic invertebrates）生物量与叶片分解速率（leaf break-down rate），并提升了水体营养盐浓度。此外，早期资源补给可提升斑尾红点鲑在次年春季的性成熟率，这表明通过消费者的数量响应，补给时间对群落长期动态具有重要调控作用。本研究结果强调，在解析资源补给对群落与生态系统过程的影响时，需充分考虑依赖于时间的消费者响应。阐明消费者有效利用脉冲式资源补给的内在机制，是进一步理解空间耦合生态系统（spatially coupled ecosystems）中群落动态的重要研究方向。 使用说明： trout_stomach：各处理组不同季节中鳟鱼的胃容物样本 trout_growth：各处理组不同季节中个体鳟鱼的特定生长速率 trout_nexcretion：各处理组不同季节中个体鳟鱼的氮排泄量 trout_pexcretion：各处理组不同季节中个体鳟鱼的磷排泄量 trout_maturity：产卵季中鳟鱼的性成熟情况 benthics：各处理组不同季节中底栖无脊椎动物的生物量 benthic algae：各处理组不同季节中底栖藻类的生物量 leaf_breakdown：各处理组不同季节中的叶片分解速率 streamwater_nutrients：各处理组不同季节中溪流水体的氨氮（NH3-N）与可溶性活性磷（SRP）浓度