The functions of species richness.

The relationships between species richness and (a) percentage plant cover, the area of ground covered by leaves, and (b) uptake of nitrogen in experimental plots in Tilman's biodiversity experiments. With increasing species richness, biomass increases and nitrogen is used up, leaving less nitrogen in the soil with more species of plants. (c) A decrease in susceptibility to invasion of temperate grasslands by exotic species with an increase in plant species richness. (d) A decrease in disease severity index for plant species in temperate grasslands with an increase in plant species richness.