Abstract：
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.
摘要：
生态学的核心辩论是关于顶级捕食者在影响其猎物的丰度和动态方面的作用的长期讨论。在陆地系统中,研究主要依靠相关方法，由于实施具有复制和适当控制的健壮实验的挑战。这样做的结果是，我们在很大程度上缺乏对相互作用物种的种群动态的机械理解，这可能令人惊讶地复杂。机械模型提供了一个机会来检查某些复杂性的原因和后果。我们提出了一个三养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，并且使用两个以体重为表型性状的积分投影模型（IPM）对草食动物和食肉动物物种进行建模。在每个IPM内，人口统计学功能是根据生物能量原理构建的，描述动物如何获取资源并将其转化为体重，能源储备和育种潜力。我们对这个模型进行参数化，以再现草的种群动态，美国北部黄石公园的麋鹿和狼，并研究了狼的重新引入对系统的影响。我们的模型产生的预测与狼重新引入之前和之后的黄石地区观察到的麋鹿和狼的种群大小非常吻合。将狼引入到我们的基础草麋鹿生物能量模型中，导致了99只狼的种群，在平衡时，麋鹿数量减少了61%(从14,948只减少到5,823只)。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3倍以上。模型中添加了狼，导致麋鹿种群从食物受限转变为捕食者受限，并对不同年份的麋鹿数量产生了稳定作用。狼的捕食也导致了麋鹿种群表型组成的转变,通过麋鹿平均体重的小幅增加。我们的模型代表了一种研究捕食者-食饵相互作用的新方法。明确考虑和联系生物能学，人口统计学和体重表型可以为复杂生态系统过程背后的机制提供新的见解。
