Complex Ecosystems Lose Stability When Resource Consumption Is Out of Niche

Natural communities display a rich variety of dynamics, including global stability, multistability, periodic oscillations, and chaotic fluctuations in species abundances. While phenomenological models (e.g., generalized Lotka-Volterra dynamics) can replicate these dynamic behaviors, understanding biological reasons behind the phenomena requires modeling mechanistic interactions. In this study, we employ a simple mechanistic framework wherein numerous species compete for various resources. We discover that a broad spectrum of dynamics emerges when species consume resources that minimally contribute to their own growth—a scenario absent in the traditional MacArthur resource-consumer model. As the discrepancy between growth-promoting resources and those predominantly consumed increases, the traditional regime of global stability transitions into a dynamic regime characterized by fluctuating species abundances and the presence of alternative stable states. We pinpoint the onset of instability through random matrix analysis, finding that the critical discrepancy between growth and consumption depends on the ratio of the number of species to the number of resources. By defining growth-promoting resources as the niches of species, we find a clear mechanistic interpretation: Communities lose stability when resource consumption overlaps more with the niche of species with similar resource preferences, indicating consumption outside one’s own niche. Furthermore, we reveal fundamental symmetries of stability in such systems and extend the stability criterion beyond the scope of random matrix analysis. The overlap between consumption and niche effectively captures the diversity and sizes of attraction basins across different attractor types beyond the instability transition. Thus, our framework offers predictive insights and mechanistic explanations for the complex dynamics arising from resource competition.