Data from: Human-induced biotic invasions and changes in plankton interaction networks

1.Pervasive and accelerating changes to ecosystems due to human activities remain major sources of uncertainty in predicting the structure and dynamics of ecological communities. Understanding which biotic interactions within natural multitrophic communities are threatened or augmented by invasions of non-native species in the context of other environmental pressures is needed for effective management. 2.We used multivariate autoregressive models with detailed time-series data from largely freshwater and brackish regions of the upper San Francisco Estuary to assess the topology, direction and strength of trophic interactions following major invasions and establishment of non-native zooplankton in the early 1990s. We simultaneously compared the effects of fish and clam predation, environmental temperature, and salinity intrusion using time-series data from > 60 monitoring locations and spanning more than three decades. 3.We found changes in the networks of biotic interactions in both regions after the major zooplankton invasions. Our results imply an increased pressure on native herbivores; intensified negative interactions between herbivores and omnivores; and stronger bottom-up influence of juvenile copepods but weaker influence of phytoplankton as a resource for higher trophic levels following the invasions. We identified salinity intrusion as a primary pressure but showed relatively stronger importance of biotic interactions for understanding the dynamics of entire communities. 4.Synthesis and applications. Our findings highlight the dynamic nature of biotic interactions and provide evidence of how simultaneous invasions of exotic species may alter interaction networks in diverse natural ecosystems over large spatial and temporal scales. Efforts to restore declining fish stocks may be in vain without fully considering the trophic dynamics that limit the flow of energy to target populations. Focusing on multitrophic interactions that may be threatened by invasions rather than a limited focus on responses of individual species or diversity is likely to yield more effective management strategies.

1. 人类活动引发的生态系统广泛且加速的改变，仍是预测生态群落结构与动态过程中不确定性的核心来源。为制定高效的生态管理策略，我们亟需明确：在多重环境压力的背景下，自然多营养级群落（multitrophic communities）内的哪些生物相互作用（biotic interactions）会因外来物种入侵而受到抑制或强化。
2. 本研究依托旧金山河口（San Francisco Estuary）上游大片淡水与咸淡水区域的长时间序列监测数据，构建多元自回归模型（multivariate autoregressive models），以评估1990年代早期非本土浮游动物（non-native zooplankton）大规模入侵并定殖后，营养级相互作用（trophic interactions）的拓扑结构、作用方向与强度。同时，我们利用覆盖60余个监测点位、跨度超30年的时序数据，对比分析了鱼类与双壳类捕食（fish and clam predation）、环境温度以及盐度入侵（salinity intrusion）的调控效应。
3. 研究结果显示，此次大规模浮游动物入侵后，两个研究区域的生物相互作用网络均发生了显著改变。具体而言，本土植食动物（native herbivores）面临的生存压力有所上升；植食动物与杂食动物（omnivores）之间的负相互作用进一步加剧；幼龄桡足类（copepods）的上行调控效应（bottom-up influence）显著增强，而浮游植物（phytoplankton）作为更高营养级的食物资源，其上行调控效应则有所减弱。本研究同时确认盐度入侵是首要的环境压力，但也证实生物相互作用在解析整个群落动态方面的重要性相对更高。
4. 综合与应用。本研究结果凸显了生物相互作用的动态本质，并证实外来物种的同步入侵可在大空间与时间尺度上，重塑多样自然生态系统中的相互作用网络。若未充分考虑限制能量流向目标种群的营养级动态（trophic dynamics），修复衰退鱼类种群（declining fish stocks）的相关举措可能徒劳无功。相较于仅聚焦单个物种或多样性的响应，将管理重心放在可能受入侵威胁的多营养级相互作用（multitrophic interactions）上，更有望制定出更为高效的生态管理策略。