Can there be more predators than prey?

One of the few general “theorems” of ecology is the statement that in a given habitat there can be no more species present than the number of limiting resources. Our aim is to examine several of the versions of this “theorem” present in the literature, to compare them and to consider the underlying assumptions and definitions so as to decide to what ecological situations the theorem is applicable. Firstly, we present three examples where the bald statement, “There can be no more species than resources” seems false, in order to illustrate the difficulty of deciding how many resources are present. Secondly, we review three versions of the theorem, point out their limitations and relate them to each other.