Before revision:  We confirm that a wide range of ecological models become unstable at the point predicted by May , even when the models do not strictly follow his assumptions. Surprisingly, increasing the interaction strength or diversity beyond the May threshold results in a URLanization of the ecosystem -- through extinction of a fixed fraction of species -- into a new stable state whose properties are well described by purely random interactions. This URLanized state remains stable for arbitrarily large ecosystem and suggests a new interpretation of May's original conclusions: when interacting complex systems with many components become sufficiently large, they will generically undergo a transition to a "typical" URLanized, stable state .
After revision:  We confirm that a wide range of ecological models become unstable at the point predicted by May , even when resource preferences have prominent designed structures. We test these ideas using numerical simulations on a wide variety of ecological models. Our work offers an explanation for the success of random consumer-resource models in reproducing experimentally observed ecological patterns in microbial communities and highlights the difficulty of scaling up bottom-up approaches in synthetic ecology to diverse communities .