Variety in evolutionary strategies favours biodiversity in habitats of moderate productivity

The mechanism whereby biodiversity varies between habitats differing in productivity is a ‘missing link’ between ecological and evolutionary theory with vital implications for biodiversity conservation, management and the assessment of ecosystem services. A unimodal, ‘humped-back’ relationship, with biodiversity greatest at intermediate productivities, is evident when plant, animal and microbial communities are compared across productivities in nature. However, the mechanistic, evolutionary basis of this observation remains enigmatic. We show, for natural and semi-natural plant communities across a range of bioclimatic zones, that biodiversity is greatest where communities include species with widely divergent values for phenotypic traits involved in ‘resource economics’ and reproductive timing, coinciding with intermediate biomass production, whilst each productivity extreme is associated with small numbers of specialised species with similar trait values. Our data demonstrate that evolution can generate a greater range of phenotypes where large, fast-growing species are prevented from attaining dominance and extreme adaptation to a harsh abiotic environment is not a prerequisite for survival.