Species-area relationships emerge from the assembly of complex ecological communities

It has been a century since the species-area relationship (SAR) was first proposed as a power law to explain how species richness scales with area. There have been many attempts to explain the origin of this predominant form. Apart from the power law, numerous empirical studies also report a semi-log form of the SAR, but very few have addressed its incidence. In this work, we test whether these relationships could emerge from the assembly of large random communities. To this end, we reformulate the generalized Lotka-Volterra model replacing the interaction strength parameter by the inverse of area. This framework allows us to track the species richness values resulting from the assembly of large competitive communities over a range of areas. Our analysis demonstrates that the two most widely reported relationship forms can emerge due to differences in immigration rates and skewness towards weak interactions. We support our results regarding immigration rates through two related studies from the literature.