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.

溪流及其相邻的河岸生境构成了相互关联的陆地与水生生态系统，二者之间存在物质与能量的交换。已知顶级捕食者（apex predators）与生态系统生物多样性之间存在关联，这使我们推测，河岸-溪流系统中的此类捕食者更可能出现在溪流质量较高的区域——溪流质量高被定义为生态系统功能增强且完整性良好。在我们的淡水研究系统中，北美水獭（river otter, Lontra canadensis）和美洲水貂（mink, Neovison vison）作为顶级捕食者发挥着关键作用。我们采用多季节占据模型（multi-season occupancy modelling），在2012-2014年的3个采样年度内，对比了溪流群落中能够解释北美水獭和美洲水貂占据动态的各项特征，包括它们与其他半水生哺乳动物的相互作用。我们在美国伊利诺伊州南部的12个主要流域（面积44526平方公里）的77个位点，对所有半水生哺乳动物进行了调查。北美水獭的朴素占据率（naïve occupancy）逐年存在差异，但总体呈上升趋势；而美洲水貂的朴素占据率始终维持在较高水平（≥93.5%）。底物可利用性的增加会提高北美水獭的可检测性，而美洲水貂的检测率则因调查时段不同而存在差异。初始调查时段内，北美水獭在靠近重引入点的位点占据率更高。北美水獭的定居概率与大型无脊椎动物生物完整性指数（macroinvertebrate index of biotic integrity）、鱼类物种丰富度以及河狸的存在呈正相关。在北美水獭偏好的鱼类科类物种丰富度较高的位点，北美水獭的存续性也更强。美洲水貂更倾向于占据鱼类丰富度较高、麝鼠存在且贻贝群落指数较好的位点。综合来看，我们的结果表明，美洲水貂和北美水獭的占据率可通过猎物多样性及存在情况预测，这显示群落组成对河岸捕食者占据动态具有重要意义。最终，这些关联表明，栖息地异质性与系统稳定性对顶级捕食者的位点利用至关重要。然而，溪流系统中自下而上（bottom-up）与自上而下（top-down）作用力的相对作用仍有待阐明。