Paradox of the plankton

In aquatic biology, the paradox of the plankton is the name given to the situation where a limited range of resources (light, nutrients) supports a much wider range of planktonic organisms. The paradox stems from a result of the competitive exclusion principle (sometimes referred to as Gause's Law), which suggests that when two species compete for the same resource, ultimately only one will persist and the other will be driven to extinction. The high diversity of phytoplankton at all phylogenetic levels stands in contrast to the limited range of resources they compete with one another for (e.g. nitrate, phosphate, silicic acid, iron).

The paradox was originally described by the limnologist G. Evelyn Hutchinson, who proposed that factors such as vertical gradients of light or turbulence; symbiosis or commensalism; differential predation; or constantly changing environmental conditions may resolve the paradox. More recent work has proposed that the paradox can be resolved by factors such as: size-selective grazing ; spatio-temporal heterogeneity ; environmental fluctuations. More generally, some researchers suggest that ecological and environmental factors continually interact such that the plankton habitat never reaches an equilibrium for which a single species is favoured.