Department of Integrative Biology, Oregon State University, Corvallis, Oregon, 97330, USA.
Ecology. 2018 Jul;99(7):1591-1601. doi: 10.1002/ecy.2387. Epub 2018 Jun 11.
Describing the mechanisms that drive variation in species interaction strengths is central to understanding, predicting, and managing community dynamics. Multiple factors have been linked to trophic interaction strength variation, including species densities, species traits, and abiotic factors. Yet most empirical tests of the relative roles of multiple mechanisms that drive variation have been limited to simplified experiments that may diverge from the dynamics of natural food webs. Here, we used a field-based observational approach to quantify the roles of prey density, predator density, predator-prey body-mass ratios, prey identity, and abiotic factors in driving variation in feeding rates of reticulate sculpin (Cottus perplexus). We combined data on over 6,000 predator-prey observations with prey identification time functions to estimate 289 prey-specific feeding rates at nine stream sites in Oregon. Feeding rates on 57 prey types showed an approximately log-normal distribution, with few strong and many weak interactions. Model selection indicated that prey density, followed by prey identity, were the two most important predictors of prey-specific sculpin feeding rates. Feeding rates showed a positive relationship with prey taxon densities that was inconsistent with predator saturation predicted by current functional response models. Feeding rates also exhibited four orders-of-magnitude in variation across prey taxonomic orders, with the lowest feeding rates observed on prey with significant anti-predator defenses. Body-mass ratios were the third most important predictor variable, showing a hump-shaped relationship with the highest feeding rates at intermediate ratios. Sculpin density was negatively correlated with feeding rates, consistent with the presence of intraspecific predator interference. Our results highlight how multiple co-occurring drivers shape trophic interactions in nature and underscore ways in which simplified experiments or reliance on scaling laws alone may lead to biased inferences about the structure and dynamics of species-rich food webs.
描述驱动物种相互作用强度变化的机制是理解、预测和管理群落动态的核心。多种因素与营养相互作用强度的变化有关，包括物种密度、物种特征和非生物因素。然而，大多数关于驱动变异的多种机制的相对作用的实证检验仅限于简化实验，这些实验可能与自然食物网的动态不同。在这里，我们使用基于实地的观测方法来量化猎物密度、捕食者密度、捕食者-猎物体重比、猎物身份和非生物因素在驱动网状棘鱼（Cottus perplexus）摄食率变化中的作用。我们结合了超过 6000 个捕食者-猎物观察数据和猎物识别时间函数，在俄勒冈州的 9 个溪流地点估计了 289 个特定猎物的摄食率。在 57 种猎物类型上的摄食率表现出近似对数正态分布，很少有强相互作用，而大多数是弱相互作用。模型选择表明，猎物密度是预测特定猎物棘鱼摄食率的最重要的两个因素，其次是猎物身份。摄食率与猎物分类群密度呈正相关，与当前功能反应模型预测的捕食者饱和不一致。摄食率在猎物分类阶元之间表现出四个数量级的变化，最低的摄食率出现在具有显著防御捕食者的猎物上。体重比是第三个最重要的预测变量，在中等比例下表现出驼峰形关系，摄食率最高。棘鱼密度与摄食率呈负相关，与种内捕食者干扰的存在一致。我们的结果强调了多种共存驱动因素如何塑造自然界中的营养相互作用，并强调了简化实验或仅依赖比例定律可能会导致对物种丰富的食物网结构和动态产生有偏差的推断。
