Abstract
The relationship between ecosystem complexity and stability remains unresolved and a mechanistic explanation for the stunning levels of biodiversity observed in communities and ecosystems is still lacking. The theoretical study of the stability of ecological communities has long been dominated by the assumption that populations are homogeneous. However, populations are structured, consisting of individuals that differ in multiple traits-such as size or developmental stage-with specific energetic demands and use of space and resources. Stage-specific interactions, such as asymmetric competition for resources or predation targeting particular life stages, are widespread in nature and strongly shape ecological dynamics. Recent theoretical work further demonstrates that differences in juvenile versus adult foraging capacity and predation risk can promote the persistence of larger and more complex communities than those predicted by unstructured models. Here, we develop a general framework to integrate population structure into community stability analyses and show that stage-dependent interactions are key to stability. Specifically, while cross-stage predator-prey interactions enhance stability, competition across different stages destabilises the community. Our results offer new insights into the stability-diversity paradox by showing that stage-structured interactions can effectively increase the magnitude of negative feedbacks and compress the unstable region. Overall, we emphasise the critical role of population structure, an often neglected feature of natural systems, in the stability of ecological communities.