PT  - JOURNAL ARTICLE
AU  - Jimmy J. Qian
AU  - Erol Akçay
TI  - The balance of interaction types determines the assembly and stability of ecological communities
AID  - 10.1101/643478
DP  - 2019 Jan 01
TA  - bioRxiv
PG  - 643478
4099  - http://biorxiv.org/content/early/2019/05/20/643478.short
4100  - http://biorxiv.org/content/early/2019/05/20/643478.full
AB  - What determines the assembly and stability of complex communities is a central question in ecology. Past work has suggested that mutualistic interactions are inherently destabilizing. However, this conclusion relies on assuming that benefits from mutualisms never stop increasing. Furthermore, almost all theoretical work focuses on the internal (asymptotic) stability of communities assembled all-at-once. Here, we present a model with saturating benefits from mutualisms and sequentially assembled communities. We show that such communities are internally stable for any level of diversity and any combination of species interaction types. External stability, or resistance to invasion, is thus an important but overlooked measure of stability. We demonstrate that the balance of different interaction types governs community dynamics. Mutualisms increase external stability, diversity, and species persistence. Ecological selection increases the prevalence of mutualisms, and limits on biodiversity emerge from species interactions. Our results help resolve longstanding debates on the stability, saturation, and diversity of communities.