Emergent feedback between symbiosis form and population dynamics.

Symbiotic relationships represent prolonged physical interactions between different species and include various forms such as mutualism, commensalism, exploitation, and competition. Here, we show that the form of symbiosis may change with the densities of the symbiotic partners as they influence the costs and benefits each species experiences. In turn, the form of symbiosis is expected to influence species persistence, population dynamics, and ultimately ecosystem stability. Based on this, we introduce the theoretical concept of a density-symbiosis feedback, where population densities affect the form of symbiosis, and symbiosis form in return affects population dynamics. This dynamic interplay calls for a re-evaluation of traditional ecological concepts and a framework considering the flexibility in symbiosis forms.