Resource diversity begets stability in complex ecosystems

A fundamental paradox in ecology is the relationship between species diversity and ecosystem stability: while May’s stability condition predicts that species diversity destabilises communities, many diverse ecosystems in nature are stable. Here, we resolve this paradox by explicitly modelling the resource dynamics that control species diversity, which May neglects. Although increasing resource diversity can increase species diversity (the competitive exclusion principle) and thus should destabilise communities according to May, we find the opposite: resource diversity consistently generates stable, species-rich communities. Furthermore, we show that contrary to the prevailing belief that interaction heterogeneity is always destabilising, different biological sources of interaction variance have opposing effects on stability. Our analytically derived stability condition showed that, consistent with previous work, stability is always induced when the correlation between growth and consumption exceeds the square root of species packing ratio (the number of surviving species/the number of surviving resources). Our work overturns a longstanding view in theoretical ecology, and demonstrates that resource dynamics are not just negligible background but are central drivers of ecosystem stability.