Data from: Stream community richness predicts apex predator occupancy dynamics in riparian systems

Streams and adjacent riparian habitats represent linked terrestrial and aquatic ecosystems that exchange materials and energy. Recognized relationships among apex predators and ecosystem biodiversity led us to hypothesize that these predators in riparian-stream systems were more likely to be found in sites with high stream quality, defined as increased ecosystem function and integrity. In our freshwater study system, river otter (Lontra canadensis) and mink (Neovison vison) play critical roles as apex predators. We used multi-season occupancy modelling across 3 sampling years (2012-2014) to compare aspects of the stream communities that explain occupancy dynamics of river otter and mink, including their interactions with other semi-aquatic mammals. We surveyed for semi-aquatic mammals at 77 sites in 12 major watersheds in southern Illinois, USA (44,526 km²). Naïve occupancy differed among years but generally increased for river otter, and remained high (≥93.5%) for mink. Increasing substrate availability increased detectability of river otter, whereas mink detection varied by survey period. Occupancy of river otter during the initial survey period was higher in sites closer to reintroduction points. Probability of colonization of river otter was positively associated with macroinvertebrate index of biotic integrity, fish species richness, and beaver presence. Sites with high species richness of fish families preferred by river otter also had increased river otter persistence. Mink occupied sites with increased fish richness, muskrat presence, and mussel community index. Taken together, our results show occupancy of both mink and river otter were predicted by aspects of prey diversity and presence, indicating the importance of community composition in occupancy dynamics of riparian predators. Ultimately, these relationships suggest that habitat heterogeneity and system stability are important to apex predator site use. However, the relative role of bottom-up and top-down forcing in stream systems remains to be resolved.

溪流及其毗邻的河岸生境属于连通的陆地与水生生态系统，二者可进行物质与能量交换。学界已证实顶级捕食者（apex predators）与生态系统生物多样性间存在关联，基于此我们提出假说：河岸溪流系统中的此类顶级捕食者，更易栖息于溪流质量较高的区域——后者被定义为生态系统功能与完整性提升的生境。在本淡水研究系统中，北美水獭（Lontra canadensis）与美洲水貂（Neovison vison）作为顶级捕食者发挥着关键作用。我们采用多季占据建模（multi-season occupancy modelling）方法，对2012-2014年共3个采样年度的数据进行分析，对比可解释北美水獭与美洲水貂占据动态的溪流群落特征，包括二者与其他半水生哺乳动物的种间相互作用。我们在美国伊利诺伊州南部的12个主要流域（总面积44526平方千米）内的77个样点开展了半水生哺乳动物调查。未校正占据率（naïve occupancy）在不同年度间存在差异：北美水獭的未校正占据率整体呈上升趋势，而美洲水貂的未校正占据率始终维持在93.5%以上的高位。底质可用性提升可提高北美水獭的检测概率，而美洲水貂的检测概率则随调查时段变化。首次调查时段内，距重新引入点较近的样点的北美水獭占据率更高。北美水獭的定殖概率与大型无脊椎动物生物完整性指数（macroinvertebrate index of biotic integrity）、鱼类物种丰富度及河狸存在情况呈正相关。北美水獭偏好的鱼类科类物种丰富度较高的样点，其水獭存续概率也更高。美洲水貂的栖息样点往往具有更高的鱼类物种丰富度、麝鼠存在情况及贻贝群落指数。综合来看，我们的研究结果表明，猎物多样性与猎物存在情况可预测美洲水貂与北美水獭的占据情况，这凸显了群落组成对河岸捕食者占据动态的重要性。综上，这些关联表明生境异质性与系统稳定性对顶级捕食者的生境利用至关重要。然而，溪流系统中上行调控（bottom-up forcing）与下行调控（top-down forcing）的相对作用仍有待进一步阐明。