Feng Zhijie, Marsland Robert, Rocks Jason W, Mehta Pankaj
Department of Physics, Boston University, Boston, MA 02215, USA.
Pontifical University of the Holy Cross, Rome, Italy.
ArXiv. 2023 Mar 6:arXiv:2303.02983v1.
Ecosystems are commonly organized into trophic levels - organisms that occupy the same level in a food chain (e.g., plants, herbivores, carnivores). A fundamental question in theoretical ecology is how the interplay between trophic structure, diversity, and competition shapes the properties of ecosystems. To address this problem, we analyze a generalized Consumer Resource Model with three trophic levels using the zero-temperature cavity method and numerical simulations. We find that intra-trophic diversity gives rise to "emergent competition" between species within a trophic level due to feedbacks mediated by other trophic levels. This emergent competition gives rise to a crossover from a regime of top-down control (populations are limited by predators) to a regime of bottom-up control (populations are limited by primary producers) and is captured by a simple order parameter related to the ratio of surviving species in different trophic levels. We show that our theoretical results agree with empirical observations, suggesting that the theoretical approach outlined here can be used to understand complex ecosystems with multiple trophic levels.
生态系统通常被组织成营养级——在食物链中占据相同层级的生物（例如，植物、食草动物、食肉动物）。理论生态学中的一个基本问题是营养结构、多样性和竞争之间的相互作用如何塑造生态系统的特性。为了解决这个问题，我们使用零温度腔方法和数值模拟分析了一个具有三个营养级的广义消费者-资源模型。我们发现，由于其他营养级介导的反馈，营养级内的多样性会导致营养级内物种之间产生“涌现竞争”。这种涌现竞争导致了从自上而下控制 regime（种群受捕食者限制）到自下而上控制 regime（种群受初级生产者限制）的转变，并由一个与不同营养级中存活物种比例相关的简单序参量来描述。我们表明，我们的理论结果与实证观察结果一致，这表明这里概述的理论方法可用于理解具有多个营养级的复杂生态系统。
