Department of Biology, University of Oxford, Oxford, UK.
Animal Ecology Unit, Research and Innovation Centre (CRI), Fondazione Edmund Mach, San Michele all'Adige, Italy.
Ecology. 2024 Jan;105(1):e4197. doi: 10.1002/ecy.4197. Epub 2023 Nov 23.
A central debate in ecology has been the long-running discussion on the role of apex predators in affecting the abundance and dynamics of their prey. In terrestrial systems, research has primarily relied on correlational approaches, due to the challenge of implementing robust experiments with replication and appropriate controls. A consequence of this is that we largely suffer from a lack of mechanistic understanding of the population dynamics of interacting species, which can be surprisingly complex. Mechanistic models offer an opportunity to examine the causes and consequences of some of this complexity. We present a bioenergetic mechanistic model of a tritrophic system where the primary vegetation resource follows a seasonal growth function, and the herbivore and carnivore species are modeled using two integral projection models (IPMs) with body mass as the phenotypic trait. Within each IPM, the demographic functions are structured according to bioenergetic principles, describing how animals acquire and transform resources into body mass, energy reserves, and breeding potential. We parameterize this model to reproduce the population dynamics of grass, elk, and wolves in northern Yellowstone National Park (USA) and investigate the impact of wolf reintroduction on the system. Our model generated predictions that closely matched the observed population sizes of elk and wolf in Yellowstone prior to and following wolf reintroduction. The introduction of wolves into our basal grass-elk bioenergetic model resulted in a population of 99 wolves and a reduction in elk numbers by 61% (from 14,948 to 5823) at equilibrium. In turn, vegetation biomass increased by approximately 25% in the growing season and more than threefold in the nongrowing season. The addition of wolves to the model caused the elk population to switch from being food-limited to being predator-limited and had a stabilizing effect on elk numbers across different years. Wolf predation also led to a shift in the phenotypic composition of the elk population via a small increase in elk average body mass. Our model represents a novel approach to the study of predator-prey interactions, and demonstrates that explicitly considering and linking bioenergetics, population demography and body mass phenotypes can provide novel insights into the mechanisms behind complex ecosystem processes.
生态学界的一个核心争论一直是关于顶级捕食者在影响其猎物丰度和动态方面的作用的长期讨论。在陆地系统中，由于缺乏具有可复制性和适当对照的稳健实验实施，研究主要依赖于相关性方法。其结果是，我们在很大程度上缺乏对相互作用物种种群动态的机制理解，而这些理解可能非常复杂。机制模型为检验一些复杂性的原因和后果提供了机会。我们提出了一个三营养级系统的生物能量机制模型，其中主要植被资源遵循季节性生长函数，而食草动物和食肉动物物种则使用两个带有身体质量作为表型特征的整体投影模型 (IPM) 进行建模。在每个 IPM 中，人口统计函数根据生物能量原理构建，描述了动物如何获取和将资源转化为身体质量、能量储备和繁殖潜力。我们对该模型进行参数化，以再现美国黄石国家公园北部的草、麋鹿和狼的种群动态，并研究狼重新引入对系统的影响。我们的模型生成的预测结果与黄石公园狼重新引入前后麋鹿和狼的实际种群规模非常吻合。在我们的基础草-麋鹿生物能量模型中引入狼，导致狼的数量达到 99 只，而麋鹿的数量减少了 61%（从 14948 只减少到 5823 只），达到平衡。反过来，植被生物量在生长季节增加了约 25%，在非生长季节增加了三倍多。模型中加入狼使麋鹿种群从食物限制转变为捕食者限制，并对不同年份的麋鹿数量产生稳定作用。狼的捕食也导致麋鹿种群的表型组成发生变化，因为麋鹿的平均体重略有增加。我们的模型代表了一种研究捕食者-猎物相互作用的新方法，并证明了明确考虑和链接生物能量、种群动态和身体质量表型可以为复杂生态系统过程背后的机制提供新的见解。
