Monaco Cristián J, Wethey David S, Helmuth Brian
Department of Biological Sciences, University of South Carolina, Columbia, South Carolina, United States of America.
Marine Science Center, Northeastern University, Nahant, Massachusetts, United States of America.
PLoS One. 2014 Aug 28;9(8):e104658. doi: 10.1371/journal.pone.0104658. eCollection 2014.
We present a Dynamic Energy Budget (DEB) model for the quintessential keystone predator, the rocky-intertidal sea star Pisaster ochraceus. Based on first principles, DEB theory is used to illuminate underlying physiological processes (maintenance, growth, development, and reproduction), thus providing a framework to predict individual-level responses to environmental change. We parameterized the model for P. ochraceus using both data from the literature and experiments conducted specifically for the DEB framework. We devoted special attention to the model's capacity to (1) describe growth trajectories at different life-stages, including pelagic larval and post-metamorphic phases, (2) simulate shrinkage when prey availability is insufficient to meet maintenance requirements, and (3) deal with the combined effects of changing body temperature and food supply. We further validated the model using an independent growth data set. Using standard statistics to compare model outputs with real data (e.g. Mean Absolute Percent Error, MAPE) we demonstrated that the model is capable of tracking P. ochraceus' growth in length at different life-stages (larvae: MAPE = 12.27%; post-metamorphic, MAPE = 9.22%), as well as quantifying reproductive output index. However, the model's skill dropped when trying to predict changes in body mass (MAPE = 24.59%), potentially because of the challenge of precisely anticipating spawning events. Interestingly, the model revealed that P. ochraceus reserves contribute little to total biomass, suggesting that animals draw energy from structure when food is limited. The latter appears to drive indeterminate growth dynamics in P. ochraceus. Individual-based mechanistic models, which can illuminate underlying physiological responses, offer a viable framework for forecasting population dynamics in the keystone predator Pisaster ochraceus. The DEB model herein represents a critical step in that direction, especially in a period of increased anthropogenic pressure on natural systems and an observed recent decline in populations of this keystone species.
我们提出了一种针对典型关键捕食者——潮间带海星赭色海星（Pisaster ochraceus）的动态能量收支（DEB）模型。基于第一原理，DEB理论用于阐明潜在的生理过程（维持、生长、发育和繁殖），从而提供一个预测个体对环境变化反应的框架。我们使用文献数据和专门为DEB框架进行的实验对赭色海星的模型进行了参数化。我们特别关注该模型的能力：（1）描述不同生命阶段的生长轨迹，包括浮游幼虫和变态后阶段；（2）在猎物可用性不足以满足维持需求时模拟萎缩；（3）处理体温变化和食物供应的综合影响。我们使用独立的生长数据集进一步验证了该模型。通过使用标准统计量将模型输出与实际数据进行比较（例如平均绝对百分比误差，MAPE），我们证明该模型能够跟踪赭色海星在不同生命阶段的体长生长（幼虫：MAPE = 12.27%；变态后，MAPE = 9.22%），以及量化繁殖输出指数。然而，在尝试预测体重变化时，该模型的技能有所下降（MAPE = 24.59%），这可能是因为精确预测产卵事件具有挑战性。有趣的是，该模型表明赭色海星的储备对总生物量贡献不大，这表明当食物有限时，动物会从身体结构中获取能量。后者似乎驱动了赭色海星的无限生长动态。基于个体的机制模型能够阐明潜在的生理反应，为预测关键捕食者赭色海星的种群动态提供了一个可行的框架。本文中的DEB模型代表了朝着这个方向迈出的关键一步，特别是在人为对自然系统压力增加以及近期观察到这种关键物种数量下降的时期。
