Huisman and Weissing reply

The earlier findings3,4,5 quoted by Lundberg et al. are interesting because they show that multiple species can coexist on a single biotic resource. However, biotic resources are irrelevant to an explanation of the plankton paradox. This paradox is concerned with phytoplankton1, and phytoplankton species do not compete for biotic resources — they use abiotic resources such as nitrogen, phosphorus, silicon, iron and light.

Also, the mechanisms that generate the fluctuations differ. The models to which Lundberg et al. refer consider predators competing for biotic prey. It is well known that predator–prey interactions easily generate fluctuations6. The fluctuations that we investigated, however, are not predator–prey oscillations. We discovered that models of competition for abiotic resources2,7 may also generate fluctuations, and that these competitive fluctuations allow a high species diversity. We have therefore shown that competition itself can generate the fluctuations that favour species coexistence. This resolves the plankton paradox.

Apart from these differences with the earlier findings3,4,5 in terms of the type of resource and the source of the fluctuations, there is an important similarity, as pointed out by Lundberg et al. All of these studies indicate that non-equilibrium dynamics generated by species interactions can have a major impact on biodiversity.